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Old 08-01-2006, 11:59 PM   #1
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My 10 Amp PCM IGN fuse keeps shorting???

So I was driving the car the other day, and I came off of a stop sign, I heard a pop, and then the car died. It would crank, but not start. I get the car home, try to hook up the scanner, and the scanner would not connect. So I pull the PCM IGN fuse, and its blown. I went to the store and bought the 10 amp fuse, put it back in the fuse box, and tried to crank the car. Same thing car cranks, doesnt start. Pull the fuse, and the second fuse is blown! What the hell could be the problem. It got too late, but tomorrow I am going to go back to the store and buy just a pack of 10 amp fuses and see if it blows when I turn the key, or if it blows when I try to crank the car. Has anyone had any sort of problems like this? I have the service manual so I am trying to trace the grounds which is a PITA. Any help/ideas would be helpful. Thanks
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Old 08-02-2006, 12:35 AM   #2
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Re: WTF? My 10 Amp PCM IGN fuse keeps shorting???

well, i put in a 20 amp fuse, and the I heard the fuel pump prime, and the car started for a second, then blew the fuse. I replaced it with a 15 amp fuse just to try and read the code, and as soon as I turned the key to the run position it fried that fuse. Upped the fuse to a 25 amp, again just to try to scan for codes, and again the fuse got fried. I am going to start checking grounds and drop the panel below the steering wheel to see if there are any crossed wires.
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Old 08-02-2006, 06:41 AM   #3
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Re: WTF? My 10 Amp PCM IGN fuse keeps shorting???

While I can't really give much input on why the fuse is blowing, I will say that you are playing with fire[ and risking one! ] by replacing a 10 amp fuse with a 25 amp fuse... [even for a few secs, to do tests, etc..] be careful..
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Old 08-02-2006, 06:53 AM   #4
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Re: WTF? My 10 Amp PCM IGN fuse keeps shorting???

I don't understand why this GD bulletin board keeps asking me to log in repeatedly. I just spent 25 minutes explaining how to find your short to ground only to have the board ask me to log in again and lost everything I typed.

When I get to work, I will post exactly how to go about find the problem. I got to go.

BS board.

Luckily I'm self employed. Even if I can't spell.
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Old 08-02-2006, 10:32 AM   #5
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Re: My 10 Amp PCM IGN fuse keeps shorting???

Look in your Owner's Manual and it will tell you what's on that circuit. Obvioulsy the PCM, but also the EVAP purge flow switch, and the tranny controls (you don't list whether its an A4 or M6.... generally helps to have the "signature" include basic info - year, model, tranny type. That way people don't have to assume your screen name accurately reflects the car).
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Old 08-02-2006, 04:09 PM   #6
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Re: My 10 Amp PCM IGN fuse keeps shorting???

In the passenger kick panel is a white 10 pin connector. Un plug it and with the fuse out, ohm the pink wire (meter set to low ohms scale) to ground. One side of the connector will go to the fuse holder and the other will go to the PCM, the EGR solenoid and the tranny. Your problem will be that the reading of the pink wire will be close if not actually 0 ohms. It should be infinite or at least very high meg ohms.

You can also do it from the fuse block as well. With the fuse out, turn the key on. One side of the fuse plug will have 12 volts, the other side will have nothing and that is the side you want to ohm to ground. If you un plug C220(the white 10 pin connector) in the kick panel and the problem is gone, the short is from C220 to the PCM or the EGR solenoid or the tranny. If it stays low when C220 is disconnected, the problem is from the fuse panel to the connector. Also try disconnecting the PCM and the EGR solenoid to be sure one of those is not causing the problem. But, based on what you stated about blowing the 25 AMP fuse, it is very unlikely they are causing the problem.

The easiest way to find the short is set the meter so you can see or hear it if it beeps. And wiggle wires in the path until the meter changes. Concentrate on areas where the harness bends or passes thru or under something.
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Old 08-02-2006, 04:25 PM   #7
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Re: WTF? My 10 Amp PCM IGN fuse keeps shorting???

Quote:
Originally Posted by Mtrhds94Z
While I can't really give much input on why the fuse is blowing, I will say that you are playing with fire[ and risking one! ] by replacing a 10 amp fuse with a 25 amp fuse... [even for a few secs, to do tests, etc..] be careful..
It's a good way to make a bad situation even worse. Fuses are there to protect the wiring. Putting a larger fuse in just risks destroying your wiring. Smoke the wiring and you will really see what trouble is.

If you have a service manual, you should be armed with all the information you need to track it down.
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Old 08-02-2006, 08:36 PM   #8
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Re: My 10 Amp PCM IGN fuse keeps shorting???

ok thanks for the info i will break out the multimeter and start checking it out
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Old 08-02-2006, 08:48 PM   #9
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Re: My 10 Amp PCM IGN fuse keeps shorting???

Use a test light, ground the test light put it where your fuse was and start pulling off connectors that are on that circuit. When the test light goes off you have narrowed you problem to one part of the circuit.

I hope you know what I'm talking about, maybe somebody else can explain it better.
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Old 08-02-2006, 08:54 PM   #10
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Re: WTF? My 10 Amp PCM IGN fuse keeps shorting???

Quote:
Originally Posted by shoebox
Smoke the wiring and you will really see what trouble is.
I agree....you should NEVER let the smoke out of wiring or electronics. It's supposed to stay in there.

They're right about upping the fuse amperage, though, nothing but problems. Blowing a 25 amp fuse HAS to be a direct short somewhere.

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Old 08-02-2006, 10:21 PM   #11
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Re: My 10 Amp PCM IGN fuse keeps shorting???

According to my service manual the only thing on this fuse is the PCM and the transmission.
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Old 08-02-2006, 10:39 PM   #12
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Re: My 10 Amp PCM IGN fuse keeps shorting???

well I disconnected the 10 pin connector. I think it must be different in a 97 because it was 5 wires in and 5 wires out on the passenger side. I did the ohm check on the fuse, and it was the same (-4.6 ohm) with the wires disconnected. So the problem must be in between the fuse box and the connector on the passenger side. I pulled the fuse box, everything seems to be tight, I cant find any loose wires. I guess I should check my grounds, is there any sort of guide online telling me where the main grounds are at? Its odd I cant seem to find anything wrong. Also does anyone know if that wire from fuse 13 runs through the engine compartment?
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Old 08-02-2006, 10:40 PM   #13
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Re: My 10 Amp PCM IGN fuse keeps shorting???

BTW the car is a 1997 z28 A4
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Old 08-03-2006, 06:13 AM   #14
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Re: My 10 Amp PCM IGN fuse keeps shorting???

Your problem is not a bad ground. Your problem is not a loose wire. The problem is the pink wire is touching ground. As I mentioned it is probably where it either turns a corner, or runs thru or under something. Like going thru the fire wall etc.....If the fuse panel is in the cabin and it powers the EGR, PCM and tranny, of course it goes thru the engine compartment. You will most likely have to check the entire length of the pink wire from the fuse block to the EGR solenoid to the PCM etc....

The area behind the passenger kick panel has 4 connectors.

The pink wire passes thru the cabin to the engine compartment on the right side of the dash. If you take out the PCM, you can see it better.

WTH is -4.6 ohms?????? Did you measure something with the power on?
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Old 08-03-2006, 08:41 PM   #15
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Re: My 10 Amp PCM IGN fuse keeps shorting???

Quote:
Originally Posted by speedygonzales
Your problem is not a bad ground. Your problem is not a loose wire. The problem is the pink wire is touching ground. As I mentioned it is probably where it either turns a corner, or runs thru or under something. Like going thru the fire wall etc.....If the fuse panel is in the cabin and it powers the EGR, PCM and tranny, of course it goes thru the engine compartment. You will most likely have to check the entire length of the pink wire from the fuse block to the EGR solenoid to the PCM etc....

The area behind the passenger kick panel has 4 connectors.

The pink wire passes thru the cabin to the engine compartment on the right side of the dash. If you take out the PCM, you can see it better.

WTH is -4.6 ohms?????? Did you measure something with the power on?
thanks for the info again. I dont know what is going on with the -4.6 ohms, thats what the mulitmeter read. I did exactly like you typed and put the positive terminal of the multimeter in the fuse connector which did not have the 12 volt reading. It also read the same -4.6 ohms when I disconnected that 4 pin connector behind the kick panel. Did I mis read something, because I thought you were saying that if the multimeter read the same with the connector disconnected, then the problem was with the wire from in between the fuse box to the connector on the passenger side, which would make sense. I dont know, I suck at electrical problems. The only other one I had was with the TPS wire grounding out on the alternator bracket. Again Speedy thanks for all of you help and info. I will try to trace that pink wire through the cabin and further.
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