Mechanics

FUSE BLOWS

2001 Dodge Caravan

Electrical problem
2001 Dodge Caravan 6 cyl All Wheel Drive Automatic 90000 miles

While I was removing the negative terminal clamp from my old battery the radio, lights and lots of relay clicking occurred. (Ignition key was removed). I installed my new battery and could no longer start my car.
I found the 10 amp ign fuse blown. Replaced it and now the system seemed normal until I moved the key to the start mode. The engine started but died as soon as the 10 amp fuse blew.
I removed the engine start relay and the fuse again blew as soon as the key was put to start.
I removed all relays and the same thing happens.
I put the key in the run mode, car in park, and jumped contacts 30 and 87 on the start relay. The engine turned over but would not run. I suspect that some module needs the 12 volts from the Ign start switch.
My Haynes manual does not show where the 12 volts from the ign switch goes other than to the engine start relay.
My car is now at the Dodge dealer has been there over a week and they tell me I need to have the ignition switch changed. I know this must be nonsense as the switch will send the 12 volts to the start relay and the car will run until the fuse blows. I need to know what module gets the 12 input from the start contacts of the ignition switch.
Can you help Thanks Benny
Avatar
Benniefum
March 21, 2009.




Hi Benny; Randy here. The ignition switches do give a lot of trouble but usually not for being intermittently shorted; they usually develop bad contacts. There are multiple switches built into it that send voltage to a lot of different places. In particular, the 12 volts goes to one pin of the engine computer to " wake it up". Another pin gets 12 volts from the Automatic Shutdown (ASD) relay as proof the relay turned on, and a third pin has 12 volts all the time for the fuel trim and fault code memory. The engine won't run if any of these voltages are missing.

Since the problem started right after changing the battery, start by looking at the terminals to see if a wire broke off or if a wire got pinched under the battery. Another problem that has been popping up more and more is a wire rubbed through in the harness under the battery tray. A bare wire touches the inner fender where the paint is rubbed off. This harness moves a little every time the engine rocks from accelerating and changing to reverse. This could have been a problem that was just days from showing up, but by disturbing the battery cables, the harness moved just enough to cause the problem to occur now. The secret here is that it's intermittent. A defective component would cause the fuse to blow right away.

To add to the misery, there are a few models of radio that have a 100 percent failure rate, but the occurrence of the problem is often sped up by disconnecting the battery. (Doesn't CAUSE the problem, just makes it happen sooner). Of course a lot of technicians get the blame for damaging these radios when they change the battery. These radios have three tone controls with yellow leds, and will only have a cd player or cassette player, never both. Glad that didn't happen to your radio. You must have a better model.

Another potential problem occurs when the electrical connection is broken many times in a few seconds such as when wiggling the battery cable back and forth while loosening the bolt. There can be dozens of computers on your van. Every one of them has a memory circuit and a power supply regulator built in. The heart of each computer module is the microprocessor. Just like in your home computer, everything must be set to the starting position when power is first applied; kind of like booting up your home computer. This is done with transistors in a " Reset" circuit. These transistors are only capable of handling a few thousandths of an amp of current, but they must pass over a full amp when power is first applied. Normally these transistors would short from the excessive current and heat, but the process is over so quickly, no damage is done. However, by allowing the electrical connection to come and go many times while working with the battery cable, these reset transistors do their thing every time the connection is made. Instead of operating once every few years, they're operating dozens of times in a fraction of a second. The heat generated can destroy them very quickly. This used to happen in some older radios too due to bad solder connections that caused the 12 volts to turn on and off very often due to vibration. Since your van seems to run ok at times, I suspect no computers got damaged, but in the future, when you loosen or tighten battery cables, hold sideways pressure on them so the electrical connection is only made or broken once. This is one of the many tidbits of knowledge you pay your technician to know.

Be thankful you don't have a Volkswagen or newer GM vehicle. Simply removing the battery cable or running the battery dead will result in a few hundred dollar towing and repair bill. There's a reason they can't sell there cars any more. People are getting wise. That's also the reason my newer cars sit at home and I drive an old rusty trusty '88 Grand Caravan.

By the way, I don't know if you're aware of it or not, but you greatly narrowed down the location of the problem by noticing that the fuse still blew after removing all the relays. That eliminated about 90 percent of the circuitry. Thank you for providing such a detailed description of the problem.

Caradiodoc

Caradiodoc
Mar 22, 2009.
Very good. The problem is not intermitant it blows the fuse everytime the ign switch is moved to the start mode.
I shall pass on to the folks at the Dodge dealer the modules that the 12 volts go to and have them remove the connector to each of the modules and then try the ign switch. When the bad module is disconnected we will replace it.
My Haynes book does not show any modules connected to the Ign switch rather usless book.
Where is the 10 amp fuse in the circuit diagram you sent me? Is it between pin 4 and pin 2 ( the short yellow wire in the diagram)?

Tiny
Benniefum
Mar 22, 2009.
My gut feeling is it's not a module but don't bet the farm on it. When you turn the ignition switch to " Run", all the modules get 12 volts from the ignition switch so a shorted module would blow the fuse before you went all the way to " Crank". In addition, as soon as you hit Run, the engine computer (powertrain control module / PCM) turns on the Automatic Shutdown (ASD) relay for two seconds. This relay sends voltage to the ignition coils, fuel injectors, alternator field winding, fuel pump or pump relay, oxygen sensor heaters, and back to the PCM on a another terminal. None of these things typically short but there could be a grounded wire going to one of them. Grounded wires usually are caused by rubbing against sharp metal brackets, harnesses falling down onto hot exhaust parts, or wires getting pinched and crushed during other service.

During that two-second blip of the ASD relay, you might hear the fuel pump run. That is further proof nothing is shorted to ground in that circuit. The ASD relay is turned on again when the PCM sees engine rotation. If you don't hear the pump run, there could be a low resistance short, (as opposed to a dead short), that causes a small delay before the fuse blows. Some things to try are: Remove the cover from a relay and install it in the ASD socket. Squeeze the contact to power up all the stuff on that circuit. You should hear a hiss from the fuel pressure regulator, and a second person should be able to hear the fuel pump run by listening under the tank or by removing the fill cap. Hold the contact applied for half a minute. If the fuse blows after a long delay, you'll need to look at the diagram to see what's on that circuit and unplug one of them at a time.

Instead of removing the cover from a relay, you can jump the terminals with a paper clip or short piece of wire. The two terminals on the sides, and parallel to each other are for the relay's coil. You want to jump the two terminals that form the letter " T". If there's a fifth terminal in the center, it's not used in these applications.

If the fuse does not blow, move that relay, (or jumper wire), to the starter relay socket. Turn the ignition switch OFF, then squeeze the contacts to verify the starter cranks the engine. The 10 amp fuse has nothing to do with the starter circuit so you're just verifying this circuit is ok. Now turn the ignition switch to Run, then squeeze the starter relay contacts. If the engine starts and runs without blowing the fuse, the problem has to be in the ignition switch or the wire going from the ignition switch to the starter relay. Since this is such a small part of the whole system, I would expect something before this step caused the fuse to blow. Another test would be to remove the starter and the ASD relays, then turn the ignition switch to Crank and see if the fuse still blows.

If the fuse only blows in the Crank position, a trick I learned at a tv servicing class many years ago is to replace the fuse with a light bulb. Tail light bulbs work best because they will limit current to about an amp so no circuitry will be damaged. Solder or crimp two wires to thin spade terminals and plug the terminals into the fuse socket. Solder the other ends of the wires to a light bulb or use a bulb socket with wires already attached. The brightness of the bulb will indicate how much current is flowing in the circuit. Now, do whatever it takes to make the bulb go to full brightness. If it only occurs in Crank, have someone hold the switch there while you flex different parts of the wiring harness and unplug various things. When the bulb dims, you've narrowed down the location of the short.

Ignition switches have given a lot of problems in the past, but typically the contacts become overheated and don't allow enough current to pass to run things on that circuit. This usually affects power windows, the radio, and the heater fan, especially if you like to use the highest fan speed often. In the worst case, the plastic housing around the electrical contacts or the electrical connector will melt. Although I've never seen it, I could imagine a switch melting enough that a ground terminal touches the starter terminal. On older cars, there was a switch built into the ignition switch that grounded the parking brake warning light to turn it on as a bulb test in the Crank position. I looked at a '99 Dakota service manual which uses the same ignition switch, and I don't see any ground wire so I really don't think the switch is the problem. You might try tilting the steering wheel to see if a wire has rubbed through and is grounded. If that stops the fuse from blowing, it would be just a coincidence that it happened at the same time you changed the battery.

I'm waiting to hear about the solution.

Caradiodoc

Caradiodoc
Mar 22, 2009.
Have to add another note. I just noticed in a '94 Caravan service manual that the parking brake light is grounded during cranking for a bulb test, but there still is no ground wire in the connector. The connection is made by a brass strip under one of the mounting bolts. That means there IS a ground terminal in the switch assembly.

Although it appears the '99 Dakota doesn't use that ground circuit, (terminal # 3), I'm pretty sure all these vehicles use the same ignition switch, so if something has melted inside, I could believe a shorted switch might cause the fuse to blow on your vehicle.

Caradiodoc
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Caradiodoc
Mar 22, 2009.
Your suggesstion on the tail light bulb is one I shall use in the future. The problem the car is in the shop with the Dodge folks.
I have taken all the relays out and when the IGN switch is moved to start the 10 amp IGN fuse blows.
With the start relay removed I fed 12 volts to pin 87 which feeds the starter. The engine turned over and no fuses blew.
I am all but certain your information given to me earlier about the start voltage going to the TCM, PCM and the FCM is the place to start.
I shall have the technician remove the plugs on these three modules and put the IGN to start and see if the 10 amp fuse holds. If so we shall connect one at a time to see which ( if any of them ) is the culprit.
Lets hope the tech will work with me.
I shall keep you posted.
Thanks for your help.
Benny

Tiny
Benniefum
Mar 22, 2009.
Well I finally got my Caravan back after 13 days in the shop.
When I took the thing in to them I told them to first disconnect the remote auto start module. They said they did but one hand did not know what the second was doing so it never got done until days later, You guessed it that was the problem.
When the ignition switch was moved to the crank position the voltage went to ground through the module.
One thing good came out of all of this however. I subscribed to the Mitchell information link (cost $11.98 as I remember it for 7 days). The diagrams and information was GREAT!
Anyone out there that wants to work on their rig and needs information about it I highly recommend it.
I am a retired electronic engineer, 28 years with NASA and 18 years as a professor at our University and I can tell you the wiring diagrams are just great.
So through all of this nonsense at least something good came of it all.
Thanks for your help and I hope other folks that need information can use the Mitchell site and get as much information as I did.
Benny

Tiny
Benniefum
Mar 31, 2009.

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