My, my, my! There are some things that need to be addressed before I get your derailed thinking back on track.
"I am barely a school trained tech and with no paid experience at all, not even one day on the job", says it all. $100.00 per hour is the going rate, but I used to hand out a full page list, tiny type, double column, of all the expenses a repair shop has to deal with before the owner gets a dime. For all of those "freebies" you mentioned, which they don't have to supply unless they care about their customers, they have endless government regulations to comply with, a dozen different taxes, many of which other businesses don't pay, multiple insurances, over-priced test equipment that becomes obsolete in a year or two, and online service manuals that are only rented for over a thousand dollars per year, all so we can work on your vehicle. Once you look at my list of business expenses, you will wonder how the shops manage to stay in business by charging only $100.00 per hour. And it's only the sweat and frustration of the mechanic's that they charge for. All the people in the office and parts department don't get to charge you for anything, but they seem to want a paycheck too.
If you want your car repaired properly, go to a two-year course at a community college, (none of that useless and grossly-over-priced UTI and Wyotech), learn the basics there, get hired as a mechanic, get ten to fifteen years experience, then see how you feel when ill-informed customers assume you're out to rip them off or you're pushing unneeded services and parts. If your van has only been worked on by you, I guarantee I can find a few safety issues with the steering, suspension, and brakes, but you will never believe me if I point those things out when I'm working on it for something else. I used to see cars every day that made me shudder to think the unsuspecting owners were risking a crash and lawsuit without even knowing it. And if that should happen, whose fault will it be? The mechanic's, because he didn't point that out and make you aware of the dangerous condition.
I know how misinformed you are by your comment about someone on the internet who finds every problem in less than an hour. We know that is not true. If he is so great, why does it take him an hour to solve the problem? I've been in tv / vcr repair for over 40 years, where we diagnose down to the component level, and I was a mechanic for 16 years before teaching Automotive Technology for nine years. One of my specialty areas was Automotive Electrical, and I can tell you, with all that experience, the only problems I could consistently solve that quickly were those I had built into my live "learning experience" donated cars. There were other problems I could get people started with the right troubleshooting steps so they could determine where to START the diagnosis, but a true professional will never say they can solve every problem in an hour. Even during my ten years working for a very nice family-owned Chrysler dealership, for warranty electrical repairs, we were only allowed one hour of diagnostic time. After that we needed to get approval before they would pay for more time. All it took to get that approval is they wanted verification that we were making progress. Now, there were mechanics specializing in electrical diagnosis, with manufacturer-supplied training on those specific vehicles, with lots of experience seeing the same models and problems over and over, with factory diagnostic equipment, and access to a support help line, ... And they STILL can't diagnose most electrical problems in an hour.
I have two former students working for my city's premier automotive electrical shop with a fantastic reputation. They would laugh at the notion that even a small percentage of electrical problems can be diagnosed in an hour. The last '99 Villager I worked on was with a friend, and together we spent an entire afternoon on it. It can take an hour just to get to some of the computers under the dash, before you even think about taking a voltage reading. So get that idea out of your head right now that some internet magician, whose results you can't verify, is the only "true professional". Only a mechanic with low self-esteem would have to make such claims to boost his self image. A real professional will not try to trick you with false claims of how great he is. He will prepare you for reality by warning of how hard it can be to find the causes of most electrical problems.
Now, to get to your relays, while I can't argue that you solved something by switching a relay, my first thought is what happened to the old one? There's a pair of contacts in it that don't care if the battery or jumper cables are connected backward. There's a coil in it that typically will have a diode or resistor across it to dampen the reverse voltage spike that occurs when current is switched off. If a resistor is used, as in GM's relays, those have no polarity, so they won't be damaged by connecting the battery backward. A diode likely will become shorted, because according to how the coil is connected in the circuit, that diode is "reverse biased", meaning backward. By being in the circuit backward, no current flows through it so it's like it isn't even there. When the battery is connected backward, that diode will now be "forward biased", and excessive current through it will instantly short it so it appears like a piece of wire. There's one problem though. Relays are turned on by something, and usually that's a computer. Fuel pump relays are always turned on by the Engine Computer, and no computer is going to do anything with the battery or jumper cables connected backward. So I have to wonder what turned the relay on and how did it fail?
As for testing other relays, I can easily overlook that for a do-it-yourselfer, but if you were a mechanic, two or three mistakes like that would get you fired. (I saw that happen to the guy working next to me after many of us warned him). You don't want to pay for our services, yet you're making the same type of mistake you blame us for. There's a limited number of ways a relay can fail. The contacts can become pitted, arced, or rusty. That has nothing to do with connecting jumper cables backward. The coil can become open, as in a break in the wire. That typically occurs near the terminals the wire is soldered to, but it's extremely uncommon. That diode I mentioned can become shorted. Current will bypass the coil through that short, so the relay won't click on, but most of the time that doesn't damage the computer. It's only those pitted contacts that can cause an intermittent symptom. 99 percent of relay failures result in it not turning on at all, and that means a dead circuit, as in a dead fuel pump or dead radiator fan. You're describing an intermittent idle speed problem. There's no relay involved with that.
I don't know how you plan on testing a relay, especially for an intermittent problem, but again, that's a way for a mechanic to get fired. Shop owners don't want to have to charge their customers for your labor time when there's more efficient ways to diagnose something. You're incorrectly admitting to a sloppy diagnostic method by swapping relays, but can you think of a faster way? Now, before you assume I also promote swapping sensors, that is not the proper way. Unless, that is, you have one in your tool box. We don't buy sensors to "try". It's faster to make one or two quick voltage tests than it is to wait for the parts store to deliver the part that may not be needed. For relays suspected of causing a dead circuit, just swap two identical relays and see if a different circuit is dead now. We could do that so quickly you wouldn't have time to watch our "free" tv in the waiting room. By the way, try running a shop without those freebies you don't appreciate, and you'd be amazed at the number of complaints, lack of repeat business, and bad word-of-mouth advertising. There's a reason you find free coffee, donuts, tv, and magazines in every waiting room, whether you appreciate the thought or not.
The best I can do for you with the coolant temperature sensor is to explain how they work. If you do have a running problem that appears to be temperature-related, that only proves that sensor is working properly. The Engine Computer changes some of the things it does at certain temperatures, and it has to get that information from the CTS. If the computer is changing the behavior of a circuit based on temperature, you can't say the CTS isn't doing what it's supposed to do.
If you have a temperature gauge on the dash, that will usually use a separate one-wire sensor. That's not the one this sad story is about. On newer vehicles the dash gauges get their information from the Engine Computer, but that wasn't the case on older vehicles. You're interested in the two-wire coolant temperature sensor. There's a 5.0 volt supply inside the Engine Computer. From there, current flows through a resistor inside the computer, out a connector terminal, and to the sensor, through it, through a ground wire that's common to multiple sensors, then to ground, but through the computer first. If you understand electrical theory, you'll understand that if you unplug the sensor, you'll find 5.0 volts on the feed / signal wire. Voltage readings for this type of sensor are only valid when it is plugged in. Then, the 5.0 volts divides up between the sensor and the resistor inside the computer. There's only one component inside the sensor so failure is extremely rare on any brand of car, except that Ford managed to have a huge problem with theirs in the early '90s. That component is a temperature-dependent resistor, or "thermistor". As its temperature goes up, it's resistance goes down. That means that as the temperature goes up, the voltage you'd measure there goes down. You can read that on your scanner under "Sensor Data" as "CTS Voltage".
When you watch that voltage, the acceptable range is from 0.5 to 4.5 volts. That's theory speaking. In actual practice you might find 0.7 to 4.2 volts. At issue isn't the exact voltage. What's critical to understand is the signal voltage will never reach 0.0 volts or 5.0 volts. Those are the conditions that set diagnostic fault codes. The only way to get 5.0 volts is to unplug the sensor or have a break in either wire. A break in the ground wire is very uncommon because it only goes a short distance before it splices in with the ground wires for other sensors. A break after that splice would set multiple fault codes for all of those sensors. The only way to get 0.0 volts is to ground the signal wire. Those conditions can be intermittent but the fault codes would stay in memory. You said there's no fault codes, so we can move on.
You'll actually find 0.2 volts on the ground wire. That's due to the monitoring circuitry inside the computer.
If you watch the CTS voltage on your scanner as the engine warms up, you'll see it drop from around, ... Oh, ... Lets say 4.2 volts to around 2.2 volts or a little less, at around 150 to 160 degrees. At that point the computer switches in a different series resistor to get more accuracy. The temperature reading will stay the same on the scanner, but the voltage will pop back up to, as I recall, around 3.5 volts, then continue going down again. I have to say, "as I recall", because other than when preparing "Notes Pages" for my students to teach them theory of operation, that isn't a test I would waste my time on when customers were paying for my time.
What you need to concern yourself with is if there's a fault code related to the coolant temperature sensor, and if it's reading the correct temperature. What a fault code may not tell you is when the sensor's voltage is within the acceptable limits, but it's wrong. As long as the voltage stays between 0.5 and 4.5 volts, you will not have a code for "CTS voltage too low" or "CTS voltage too high". You could, however, have a sensor reading minus 20 degrees when it's 50 degrees outside. Minus 20 is a valid reading even though it's wrong. Where that is supposed to be detected is when the engine has been off for typically at least six hours, the computer knows the coolant temperature sensor had better be reading the same as the ambient air temperature sensor, intake air temperature sensor, or battery temperature sensor. When they are real close, that's how it learns the personality of a new sensor. When people blindly replace multiple sensors at the same time, the computer can get confused and do weird things until it learns their characteristics.
I don't like the thought of replacing a computer, but given the circumstances, and since it sounds like you have one in another vehicle, it's worth a shot. Computers cause a lot less trouble than they get blamed for. They have diodes between the 12 volt feed wires and the ground wires, but they're in there backward, so they don't do anything. When the battery or jumper cables are connected backward, that's when the diodes will be forward biased and turn on. They are supposed to draw heavy current to force fuses to blow so the rest of the circuit, and the computer, is protected. I guess I'd be happy to hear replacing the computer solved the problems, but until then, I'm skeptical.
Monday, November 9th, 2015 AT 7:15 PM
