Reversed jumper cables damage

All of the dozens of computers have a diode built in to protect them. Diodes are one-way valves for electrical current flow. They are installed backward so they are turned off all the time, except when battery cables or jumper cables are reversed. Reverse polarity puts the diodes in the circuit so they are turned on and act like a short circuit. That is a temporary condition that is designed to cause the appropriate fuse to blow, thereby protecting the rest of the circuitry. Normally the only needed repair is to replace the multiple blown fuses.

When you have a fuse that blows repeatedly, something has become totally shorted. Given the history, we can assume the short is not due to a bare wire or other things associated with age or mileage. It is likely the protective diode shorted. I can repair things like that, but it is due to my TV repair background. For mechanics and auto repair shops, the fix is to replace the radio.

Be aware too there are multiple fuses for the radio. One of them is for the clock and station preset memory when the ignition switch is off, and that circuit is always tied into some other circuit that is always live, and is labelled for that circuit, not for the radio. Most commonly that memory circuit is tied into the interior lights circuit, but on some vehicles it could be the brake lights, cigarette lighter, or horn.

The white smoke could have been steam coming from water boiling out of the battery. At five years old, your battery is about to fail anyway and is due to be replaced. Reversing the cables is very unlikely to damage a fairly new battery, and for an old one, typically, at most it will simply hasten the impending failure. I would not get excited about a battery problem if it is time to replace it anyway.

The smoke could also have been caused by an overheating wire. In the past we had "fuse link wires" which were small sections of wire spliced in that were smaller than the wires they protected, so they were the weak link in the chain, and their insulation was designed to not burn or melt. They were used specifically because they needed some time to burn open. That prevented nuisance failures and the need for the rather involved repair procedures. Fuse link wires were expected to last the life of the vehicle and were only needed for catastrophic failures. Since the mid 1990's, most vehicles use large plug-in fuses now instead of fuse link wires. Each of those protect multiple circuits that each still have their own smaller fuses. Usually those smaller fuses blow so there is no need for the large ones to blow. For that reason, when you have multiple things that do not work, it is more likely you'll find many small blown fuses and not one large fuse.

Be aware that the insane engineers have seen fit to hang an unnecessary computer onto every part of our vehicles now, and there is absolutely nothing you can name that does not have one involved. We have tire pressure monitors, (computer), heated seats and steering wheel, (upholstery / computer), heated window and mirror defrosters, (computer), and dozens more. Every one of those computers do multiple things. You should check each of those things you can identify. For example, it is critically important that dome lights fade out slowly rather than simply turn off with a switch. That means those lights are run by a computer. Door locks used to work just fine with switches. Now they are run with a computer so you can open just the driver's door or all four doors with a remote. Be sure all those functions are working correctly.

There will be some things you may need to reset to your preference, like radio stations, instrument cluster settings, and things like that. There are also some things you will need to make happen, like running an electric radiator fan. Hopefully your mechanic will check as many of those things as he can think of. That includes dash warning lights that are supposed to turn on for a few seconds when you start the engine, while those computers are running short self-tests. For example, the Check Engine, Air Bag, and Anti-Lock Brake lights should all turn on for roughly six seconds, then they must turn off and stay off. It is very unlikely circuitry associated with those computers would be damaged by reverse polarity, but that is part of what those computers test each time you turn on the ignition switch. If any warning light fails to turn on for a few seconds, or stays on while driving, given the recent history, suspect the computer, not the rest of the wiring.

Ask to have the cause of any damage and repairs documented on the repair order and the final bill. Mechanics are supposed to write their "story" on the back of the repair order. That is what is used, in part, to calculate their paycheck and your bill. Repairs that are listed in the "flat rate" guide are billed according to the amount of time the job is supposed to take, regardless if the mechanic takes longer or gets done quicker. With this type of repair when there is no way to know what is involved in diagnosis or repair, the bill is based on the actual time the mechanic is on the job. He can't lose money by being inefficient, but he cannot earn extra money by investing in expensive tools and advanced training, or by working as efficiently as possible. For this reason, an experienced mechanic is going to want to solve all the problems as quickly as possible so he can move on to other cars where he has the potential to earn more money. The checks and balances is if he overlooks something and you return to the shop, he is going to have to drop what he is doing and go back to your vehicle. He wants to avoid that, so while he wants to get everything found and solved as quickly as possible, there is an incentive for him to take his time and do it right the first time.

Related to this documenting the suspected cause of the failure, be aware a lot of people will try to get things repaired that are not related to the reversed jumper cables. The first thing to consider is your battery was run down after running the radio for just ten minutes. I just replaced the battery yesterday in my Grand Voyager. It had been running my laptop computer for fewer and fewer minutes all summer, and yesterday was the first day it got down to below twenty degrees, (low temperature is a killer for old batteries), and it would not start the engine. I knew the battery was on its last legs for months, and it would not be fair to make someone else pay for a new one. You are already fortunate to be working with a towing company that is ready to pay for their mistake. Your battery was about to fail anyway so don't balk if they do not want to cover that.

I have actually spoken with people who think they can sneak in tires and alignments, and oil changes, as being needed because of someone's mistake. Honest shops and mechanics will not do that. They will look out for the towing company just as they will for you.

Please do not be angry if you do find something that got overlooked. This could turn out to be a simple repair, as they usually do, or it could become quite involved. Shops and mechanics hate it when you have to return for the same problem, so they are going to try to avoid that, but these cars are extremely complicated. You can help by listing as many non-working things as you can remember when you talk with the service writer.

The ECU, (electronic control unit / engine control unit), and PCM, (power train control unit), are the same thing. GM typically uses "ECU", and Chrysler uses "PCM". If the engine starts and runs normally, the PCM is likely okay. It controls a real lot of other stuff, but not until it is powered up. One of those things is the CKP, (crankshaft position sensor). That is part of the external wiring for the PCM and is not going to be damaged. That sensor has to work for the engine to run.

Do not even think about starter trouble. The motor can run backward without being damaged. That does not mean it will crank the engine backward. It just means an electrical motor of this design doesn't care about polarity. Same with the solenoid built into the starter motor. It is just a big coil of wire, and it will operate with either polarity.

The alternator is a different story. They were actually developed by Chrysler for use in 1960 models, and Chrysler copyrighted the term. (Little piece of useless trivia). Today, to standardize terminology, we call them "AC generators". Electrical power can only be stored chemically in a battery, and those only store DC power. The alternating current coming out of the AC generator has to be converted to direct current, and that is done with six internal diodes, those one-way valves for electrical current flow. Unlike when they are used for protection in computers, in the alternator they are installed so current goes through them, then out to the battery and the car's electrical system. They perform a second desirable function of blocking current flow from draining the battery when the engine is not running, (and the alternator is not producing output current). These diodes are really beefy and tough. It takes a lot to destroy one, but it does happen at times. When the alternator is working, it will generate roughly 20 to 50 amps, whatever is needed to run the electrical system and recharge the battery. It is capable of developing a lot more current, up to its design value, which can be well over 100 amps. When the battery cables are reversed. Those diodes are no longer in the circuit backward and turned off to block current flow. They are "forward biased" and will act like a dead short. I mentioned those fuse link wires that were used on older vehicles. On one as new as yours, there is going to be a really large fuse bolted into the under-hood fuse box. That fuse should blow before a diode gets hot enough to short.

Your mechanic should perform a charging system test. It only takes a couple of minutes. In particular, I would like to see what is found for charging voltage, "full-load output current", and "ripple voltage".

Those diodes are in two sets of three. Any one diode in each set has to short for there to be a direct short. A somewhat common failure is for just one diode to short, then the excessive heat usually causes it to burn open, meaning it is like it is not even there in the circuit. That removes the potential for a dead short to occur if a second diode shorts, but it causes a more immediate problem. I looked up a replacement alternator for your vehicle. It came with either a 140-amp or a 160-amp alternator. (That is huge. Years ago a large, optional unit might be in the 55 to 65-amp range). Without going into all the electrical theory, all we need to know is when one diode fails, the most the alternator will be able to develop is exactly one third of its rated maximum current. The only time any alternator will develop its maximum current is during the full-load output current test. It will never do that while just running the vehicle's electrical system. The reason we do this test is to determine if there is a failed diode. The test takes the better part of three or four seconds once the tester's cables are hooked up.

When a diode has failed, one out of every three output voltage pulses is missing, and system voltage will drop slightly. This is getting too technical, but this is what is being measured with ripple voltage. A few testers will display it as a voltage, but most just show whether it is low or high. They show that on a bar graph that lights up. We want to see low ripple voltage. If you're lucky enough to get a printout with the numbers, list those numbers here and I will interpret them. If you see anything close to 130 to 140 amps, or more, for output current, the diodes are fine. Ripple voltage at that point will be irrelevant. Every time I performed this test, I wrote the numbers on the back of the repair order. It was up to the service writer whether he wanted to enter that information into his computer to show up on the invoice. You can request a hand-written list of those numbers if that is what it takes.

Be aware because of its physical properties, an alternator is incapable of developing more current than it is designed to produce, and they do not get weak and develop only slightly less than what they were designed for. That means if you find 140 amps during the full-load test, you have a good 140-amp alternator, not a weak 160-amp unit. If you have a 140-amp alternator with a bad diode, the most current you will get will be close to, uhm, lets see, about 45 amps. That is enough to run the engine and electrical system, but not under all conditions. At times the battery might have to make up the difference, and that can cause it to slowly run down over days or weeks, especially if you do a lot of slow and short-trip driving.

The battery cables are not going to be a concern. They need to pass over 200 amps to run the starter motor. You have to remember that while the jumper cables were reversed polarity and trying to make current flow the wrong way, your battery was still connected properly and was fighting the current from the jump-starting vehicle. The damage is going to be less than when someone is installing a new battery and connects the cables backward. There was probably more stress on the jumper cables than there was on your battery cables.

Thank you. I have to drive ten miles into town to sit in the library parking lot to use their wireless internet, and in the winter I do not do that every day, so do not panic if you do not hear back from me right away. Will wait to see your numbers.

Dandy. Push for the full-load output current. Remember, that test only takes a few seconds. It takes considerably longer to wheel the tester to the vehicle and connect the three cables.

"Charging the battery okay" is like saying the water supply to your house is okay because you are getting enough water to brush your teeth. You may at times also want to do a load of wash or take a shower. You wont be happy with that little trickle of water.

You do not need to be concerned with the battery's rate of charge. He will take care of that on his own. Typically, right after cranking the engine and running the battery down, it will accept a charge rate of around 20 amps, but that will quickly drop to ten or less. We consider a battery to be fully-charged when it drops to five amps or less.

If you are interested, I used water analogies with my students to make electrical theory easier to understand. Think of the municipal water tower in your town. The weight of the water in it is what creates the pressure in the pipes. Voltage is electrical pressure, but just like water sitting in the tower doesn't do any work, 12 volts sitting in a battery does not do any work either.

Once you connect some pipes and open some valves, you give the water a place to flow to. That is current flow. If you connect a rotating lawn sprinkler, that current flow will cause work to be performed, spinning the sprinkler.

Once you connect some wires and turn on some switches, you give electrical current a place to flow. If you connect a motor, it will spin, or a light bulb will light up.

Now, if you use up half of the water in the tower, you'll have less weight, and less pressure. With half the pressure, the lawn sprinkler will spin slower. We need to refill the tower to get the pressure back up, and that is done with a pump.

There is a noticeable difference when talking about the car battery. A fully-charged battery will measure 12.6 volts. When it is almost completely used up, (run dead), it will still measure around 12.2 volts, but that is enough for us to use as a gauge. Refilling the battery will raise its voltage very little, but it will seriously increase its ability to do work. We refill it with current from the alternator.

Here is where my sad story gets horrendously exciting. If you have fifty pounds of pressure in the water tower, but only fifty pounds from the pump, there is no incentive for any water to flow up into the tower. You need to have considerably higher pressure from the pump to recharge" the tower.

Likewise, you need a higher voltage from the alternator to convince current to flow into the battery. The magic number is between 13.75 and 14.75 volts. With that voltage, current will flow fast enough to quickly recharge the battery, but not so fast as to overheat the plates in it. I mentioned those diodes in the alternator already, and that if one is bad, you will only be able to get one third of its maximum rating during the full-load test. With that reduced current capacity you will still find the charging voltage to be between 13.75 and 14.75 volts. This is why simply measuring battery voltage with the engine running will tell you if the alternator is working, but it won't tell you if it is working to its full capacity. You can use an inexpensive digital voltmeter to measure the charging voltage yourself, but finding an acceptable voltage only means it is okay to perform the rest of the tests, meaning full-load output current and ripple voltage, and you need a professional load tester to do that. This is why I do not want you to accept, "it's charging the battery okay". The quick and easy voltage test will appear to be okay even if the alternator has a bad diode. We want to now the full-load output current.

As a point of great value, if you have to insist on seeing the full-load test performed, the mechanic might be on another job and will have to stop what he is doing. Most of us are happy to do that, especially when we just got done working for a paying customer, and we like to show off our skill and knowledge, but there are always the few of us who become crabby or irritated. You might consider returning a few days or a week later with a box of donuts or cookies as a "thank you". At the dealership I worked for, we had treats like that almost every week from happy customers. (Chocolate chip cookies are our favorite)!

Dandy. Remember too that ninety nine percent of electrical stuff is run by or is an input to a computer. None of that is going to be damaged. Even if the computer related to those circuits is damaged, it will not cause further damage down the line.

I understand too their comment about having to replace a computer before further testing can be done. I have a 2014 truck that wont even let me turn on the high-beam head lights unless the engine is running. I am sure the insane engineers had some reason for designing it that way, but I will never figure it out.

That's okay; I know who I am!

Library just closed and I'm sitting in my freezing van. Their wireless is not working real well tonight in the parking lot. I'll check back tomorrow to see if there's any progress.

I'm in the middle of Wisconsin. As for dollars, the web site owners do compensate me for every answer of value I submit. I used to get a portion of donations, but I don't know if that is still the case. Regardless, donations are greatly appreciated by the site owners as it is expensive to run a web site. I really like it that donations are not required.

I have a web site of my own and I just got another bill. I'm in the process of moving it to another company or just discontinuing it due to the cost. It jumped this year to over $500.00. I just spill automotive electrical information for students and instructors. I don't sell anything and I have never made a single penny on advertising.

As for batteries, I cover that on one of my web pages. To boil it down to the basics, the lead flakes off the plates over time. There is no way to avoid that, but the manufacturers know how quickly that will occur, and they use that information to provide the longest warranty period possible because that translates into more dollars they can charge for that battery. There is an area in the bottom of the battery's housing where that flaked-off lead accumulates. When it builds up high enough, typically after five years, it will short the negative and positive plates in that cell together. At that point the battery must be replaced. It will crank the engine very slowly, if at all, and if it does, it is usually too slowly for the engine to start. Even a jump-start might not work at that point because the shorted cell is still shorting out the jumping battery.

A battery can also fail before that lead builds up in the bottom of the housing enough to short the plates. The lead needs to be suspended on the plates, in the acid, to work. When half of it flakes off, the battery may still crank the engine just fine, but not for as long. A better example is when you leave your head lights on, (in the days before we had computers that turned them off for us). A fairly new battery would run those lights for about two hours before it was run down to the point it wouldn't crank the engine. By the time it's three years old, it might only run those lights for an hour, due to the less lead in the plates and therefore less room to store electrons, but it can still provide short bursts of very high current to crank the engine. I just went through this a few days ago with my van. I use a little power inverter to run my laptop when I sit in a parking lot using someone's wireless internet. Last spring I could run it for two hours or more, then start the engine and drive home. Last week it was down to less than a half hour, then, when it suddenly got cold the next day, it wouldn't even crank the engine fast enough to start. Electrical power can only be stored in a battery, and that is done chemically. Chemical reactions always slow down as temperature goes down, plus, cold engine oil gets real thick making the engine harder to crank. We need more cranking power and we're trying to get it from a battery that is weaker. That is why most battery damage occurs in hot weather, but it shows up in cold weather.

Here's the clinker. To be able to offer the longer warranty, which will cost extra, that area in the bottom of the housing that collects the flaked-off lead needs to be bigger. That means there's less room for the plates, so they have to be smaller. That isn't such a concern today when fuel injected engines start right away. Back in the '60s and '70s, with carburetors that were out-of-adjustment, it wasn't uncommon to grind on a starter for much longer before the engine finally started, especially on cold winter days. We needed batteries with plenty of lead in the plates to give us that longer cranking time.

You have to decide if the longer warranty is worth the extra expense. Only a very low percentage of any batteries fail during the warranty period. Instead, look at the length of the warranty as an indicator of how long you can expect that battery to last. Often they will fail with just a coupe of months left in the warranty. I've always been suspicious that was planned because the only way to collect on that is to receive a tiny discount on the cost of a new battery, ... From the same manufacturer. I look at it as a low-cost way to get you to buy another one of their batteries. Of course, to be fair, there are a lot of batteries that last considerably longer than their warranty period.

A few years ago I bought the cheapest Carquest battery I could find. That lasted over eight years, but now I found a better alternative. We have a battery store in my town that sells "reconditioned" batteries, but they don't advertise that, or tell you about them. You have to know about them and ask for one. One time they told me they were called "reconditioned", but they simply had been sitting on the shelf for over a year and they wanted to get rid of them. Another time they told me, as I had originally suspected, someone bought the battery, took it home and installed it them self, then found out it didn't solve the problem and they returned it. Technically it is now a used battery and can't be sold at full price.

Currently this store is selling their reconditioned batteries for $30.00 exchange. I always have a bunch of old batteries laying around. They buy them for six bucks each. Each time I need a battery, I take them six bad ones, make an even exchange, and only have to pay the sales tax.

You can also get some good deals at the larger salvage yards. The smaller yards typically buy the older cars where people keep the batteries, or they're on their last legs. The large yards buy late model insurance wrecks that are often one to three years old. They will often have more fairly new batteries than they know what to do with. My local yard sells them for $19.99.

There are a few Chrysler models that have gone to the really miserable side-post batteries that GM refuses to give up on, but I think your Jeep uses the better top posts. If so, when you look for a replacement battery, look at which corner the positive and negative posts are in. Match the new battery to that to be sure the cables will reach. Anyone at a battery store or salvage yard will know right away or they will pop your hood and look to be sure. You can replace the battery yourself, but there are some things you must be aware of. First of all, many of the computers have memories that will be lost. For example, you'll need to reset the clock and your favorite radio stations. Any diagnostic fault codes stored in the Engine Computer will be lost. That isn't a big concern, and will have occurred anyway during the current repair work. Fuel trim data will start to be rebuilt as soon as you resume driving. That takes just a few minutes and you are likely to not even notice the less-than-perfect engine performance.

What DOES worry me is there are some European import cars that have multiple computers that lock up when the battery is disconnected or run dead. That requires a very expensive tow to the dealership. GM copied that idea since they are the top manufacturer at coming up with innovations that benefit them at the expense of their customers. (Chrysler has always been the leader, since the '50s, at developing innovations that really benefit car owners, but that's a story for a different time). To avoid these problems, there are a number of "memory saver" devices on the market. Most of them plug into the cigarette lighter and use a 9-volt transistor battery to keep the computer memory circuits powered up. I use a small battery charger hooked right to the battery cables, but there are certain precautions that must be observed when doing that. I do have a 2014 Dodge truck that was smashed, and my friend rebuilt in his body shop. We did need to disconnect the battery a few times, and there was not a single indication that was done other than the incorrect clock, so I might be worrying you about nothing. You can ask your mechanic if any computers need to be unlocked after reconnecting the battery. If he says "no", you can overlook this entire paragraph.

Along with the location of the two posts on the battery, the positive post is always larger in diameter than the negative post. Use your wrench to loosen and remove the negative cable first. We do that one first only because if you slip and the wrench contacts the clamp and the body sheet metal at the same time, nothing will happen. The two are actually connected together by the smaller wire on the negative cable. If you do the positive cable first and the wrench makes contact with another metal part, there will be huge sparks, and the wrench can actually get welded in place and become red hot enough to melt and bend! Remove the positive cable last. That way, if the wrench makes contact with a metal part, nothing exciting will happen. No current can flow and cause sparks once the negative cable is already disconnected.

There will be either a bolt to loosen to loosen the hold-down bracket near the bottom of the battery, in front or in back, or there will be a strap-type bracket over the top. Once you get the new battery in, be sure whatever is used to hold the battery in place is tightened properly. If it is not, the battery will vibrate excessively. That will aid the lead in flaking off the plates, and will shorten the battery's life.

Use a post cleaner to scrape the inside of the cable clamps and the outside of the posts so they're clean and shiny and make good contact. Don't get so carried away that you grind off so much that the clamps can't be tightened enough. What you don't want to see on the contact areas is a hard black coating. That is one type of corrosion that prevents a good connection.

As a point of interest, don't let anyone sell you a pair of "juicy rings" that slide over the posts to prevent corrosion. What I have found is when a lot of the lead has flaked off the plates, as in when the battery is near the end of its life, the little lead that is left has to absorb the full charging current flow, and that makes the plates get hotter than normal. The heat causes increased gasing and bubbling of the acid, and those bubbles reach the underside of the top of the housing. From there, the acid that has splashed onto the case works its way over to the posts where it sneaks through the mechanical joints and collects right under the cable clamps. That is what causes the white corrosion that looks like cauliflower. If that corrosion hasn't shown up yet on an old battery, those juicy rings aren't going to do anything. If the corrosion has shown up, the battery can be expected to fail within the next six months, and the juicy rings aren't going to change that. When I saw that corrosion on a customer's battery during other services, like oil changes and alignments, I would include a written warning on the repair order, to expect a failure soon. Some people thought I did something to their battery to cause the failure, and that's how I knew it was going to fail.

Reconnect the positive cable first, then the negative one. The positive post, as I mentioned, is larger, it has a plus sign molded into the top right next to it, and often there will be red paint on the top of the post. The negative post is smaller, has a minus sign next to it, and when used, will have green paint on top. If you mistakenly try to put the negative cable on the positive post, it won't fit unless you spread the clamp open. That is the first clue you're about to do the same damage that is being repaired now. If you put the positive clamp on the negative post, it will be too loose.

My experience has been that computers with "customer preference" settings retain their programming when the battery is disconnected. Those settings include things like horn chirp when locking the doors with the remote, speed-activated door locks, and things like that. Tire size is programmed into the Transmission Computer so the speedometer will be calibrated correctly. That should not change, but to be safe, observe if you're going faster or slower than everyone else. I check my vehicles with the remote radar signs the cops set out periodically. Those seem to be pretty accurate.