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PCM ASD relay fuse keeps blowing on a 1996 GTS

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PCM ASD relay fuse keeps blowing on a 1996 GTS
Old April 21st, 2009, 03:10 AM   #1
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PCM ASD relay fuse keeps blowing on a 1996 GTS

I own a 1996 Viper GTS. I ran the car at the track in Las Vegas last month (3-day weekend) and then spent hours driving home (to Southern California) in stop-and-go traffic. A couple of hours after arriving home I took the car out and hand washed it (just a few miles away from home). On the way home, the car died when exiting the freeway. The oil pressue dropped to 0 and the battery and service engine soon lamps came on.

Although I'd been watching the battery voltage closely all weekend, it acted as if the battery was very weak when I tried to start the car (I've had starting problems in the past, but it was working all weekend in Las Vegas). The alarm was acting strangely (first I got locked out, then it would beep when pressing button on fob, but would not unlock doors). The radiator fan comes on and stays on whenever I put the key in the RUN position (strange and very noisy and obnoxious). I tried jump starting from my truck with no luck.

I had the car towed home. I found that there is no spark when cranking the engine. I don't know how to test fuel pressure but I tried measuring voltage at one injector (dark green/org wire) and didn't find anything (even just after turning key to START or to RUN position). Tonight I disovered that the PCM / ASD relay fuse was intermitant (just barely blown). I replaced the fuse and tried to start the car and blew the replacement fuse.

Does anyone have any ideas why the fuse might be blowing? Does this fuse run anything else besides the PCM and ASD relay? Which is more likely causing the fuse failure and is there a way to isolate these components to trouble shoot? What does the ASD (auto-shut-down) relay do?

Thank you!
Ken
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Old April 21st, 2009, 07:59 AM   #2
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I've had similar troubles in my 96 GTS after visiting the carwash on track weekends. However, I've never had it completely refuse to run. Most times, it will pop & backfire and not hold idle for a minute or so.

Gen 2s seem to be very finicky about proper grounding. Make sure you have good contact at the grounding stud on the driver's rocker sill. Also, pull your battery out and check the electrolyte level. With all the Gs you pull at the track, there's a lot of fluid sloshing out the breathers and voltage drops attendantly.
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Old April 21st, 2009, 12:07 PM   #3
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I thought I should add that I tried pulling codes. My very inexpensive OBD II reader won't read anything (gets power but display never changes from its default state - even when car is cranking; but I've never used this reader on the car when the car was working, so it could be incompatible; works fine on all my other cars).

I discovered that my CarChip Pro data logger can pull codes. When plugged in, it detects that the car is being turned on/off but doesn't log anything else; including codes. With the fuse blown to the PCM, perhaps this should be expected anyway. Not sure that codes are going to help with my blown fuse problem; just thought I should answer this question before it comes up.
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Old April 21st, 2009, 01:00 PM   #4
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Where are you located? Might be an option to have one of the member here close to you help out
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Old April 21st, 2009, 02:55 PM   #5
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Quote:
Originally Posted by GTS Dean View Post
I've had similar troubles in my 96 GTS after visiting the carwash on track weekends. However, I've never had it completely refuse to run. Most times, it will pop & backfire and not hold idle for a minute or so.

Gen 2s seem to be very finicky about proper grounding. Make sure you have good contact at the grounding stud on the driver's rocker sill. Also, pull your battery out and check the electrolyte level. With all the Gs you pull at the track, there's a lot of fluid sloshing out the breathers and voltage drops attendantly.
Thank you for the ideas. I am assuming grounding is good since the problem is that I'm blowing a fuse. The blown fuse indicates that either the PCM or ASD relay is drawing too much power (and, hence, has a good ground). In fact, it is probably more likely I have an EXTRA ground somewhere that I should not ;-)

Battery is brand new and I put a 100A quick-starter on the jump post when trying ot start; it cranks really fast. I think the blown fuse indicates I'm getting plenth of juice from the battery, rather than not enough. Thanx again.
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Old April 21st, 2009, 02:58 PM   #6
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Where are you located? Might be an option to have one of the member here close to you help out
I'm in Goleta, CA which is just north of Santa Barbara. I'm part of the So. Cal. Viper Club, but most people live in LA which is 1.5 hours away. I've thought about taking to local dealer but that means towing it; hoping to fix myself. I've ordered several manuals via eBay, but they are going to take over a week to get here so I was hoping someone here might be familar with this symptom.
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Old April 21st, 2009, 03:00 PM   #7
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Dan Cragin is down your way too, might want to give him a call. He might have some hints or ideas. DC Performance: Proven Performance
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Old April 21st, 2009, 06:53 PM   #8
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I'm going to guess there's more than one issue going on.

The ASD disengages power to the coil packs and injectors if the PCM does not detect any camshaft or crankshaft signal during engine cranking. This would explain why you are not receiving spark.

Since your fuse is almost popping, you could have a short on a circuit close to what also supplies power to the PCM. I think in most cases the PCM grounds most circuits.

Tonight I'll dig through the schematics and see if I can make an educated guess on which circuits could actually draw that amount of amperage.
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Old April 22nd, 2009, 07:27 PM   #9
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Ken:

There are three fuses associated witht he ASD. There is a 10A (#10) input fuse that feeds the coil of the ASD. There is a 20A (#15) input fuse that feeds the contacts of the ASD. That 20A circuit leaves the relay and feeds the PCM and the both downstream O2's. The O2 branch of that circuit is fused at 15A (#1). Which fuse is opening? The circuit that feeds the O2's is a possible culprit, it is sort of in harms way.
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Old April 22nd, 2009, 07:45 PM   #10
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Quote:
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Ken:

Which fuse is opening?
The one that keeps popping is #15, labeled "PCM & ASD".
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Old April 22nd, 2009, 08:56 PM   #11
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Quote:
Originally Posted by Ken Alker View Post
The one that keeps popping is #15, labeled "PCM & ASD".
That narrows it down. That circuit splits at the output of the ASD. One branch feeds the downstream O2's, but, that branch goes thru another fuse (#15), if that fuse is not blown that rules out that branch. The other branch goes to the PCM, but, it is not independently fused. logic would point to that circuit as the possible problem. To test that circuit you would have to pull the C1 plug (rear plug) on the PCM, remove the ASD, then test the pin #30 hole of of the ASD mount for a short to ground.

Another issue could be a faulty bus connection in the #15 fuse socket. Pull the relay and the #15 fuse and check the relay side of the fuse mount (hole) for a short to ground. If you have continuity to ground you have found your issue.

A third problem could be the PCM itself. That one is harder to find, but, a hall effect current probe around the wire connected to Pin 12 in the CI connector would show you what the PCM curent draw is. You would just turn the key on and start to crank the engine, any abnormal current (greater then five amps?) would point to the PCM.

I guess the dealer scan tool could tell you the same. One last item, if that #15 fuses opens it should show a soft code. The CEL will not turn on, but, a scanner should show it as ASD Malfunction.

Last edited by Jack B; April 22nd, 2009 at 09:12 PM.
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Old April 22nd, 2009, 10:16 PM   #12
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Wow, Jack. Thanx. I'm going to go poke around right now. I sure wish I had a schematic. Is there one posted on-line somewhere? Maybe its in the service manual that I don't have yet.
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Old April 23rd, 2009, 06:32 AM   #13
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Quote:
Originally Posted by Ken Alker View Post
Wow, Jack. Thanx. I'm going to go poke around right now. I sure wish I had a schematic. Is there one posted on-line somewhere? Maybe its in the service manual that I don't have yet.
One I forgot was a faulty relay, just flop the ASD relay with the fog light relay and see if that clears it up.
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Old April 24th, 2009, 12:38 AM   #14
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Old April 24th, 2009, 01:04 AM   #15
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If your in Socal and you want to drop the car by, we can definately take a look at it for you.

We've seen everything from loose connections at the PDC to wires rubbing through and becoming exposed and grounding out. A little bit of time tracing the wires and the problem should be found. You can give us a call if you don't find the underlying issue, we'd be glad to help.

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Old April 24th, 2009, 01:37 AM   #16
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I found the problem. Following are the steps I took. Some of this will be a little redundant with the hints Jack offered, but I'm putting everything here to be thorough in the event it helps someone else out in the future:

First I went to Santa Barbara Chrysler Jeep Dodge and Steve, a very competent and friendly technician, printed out every schematic page referencing fuse 15 (8 pages).

Next, I bought a handful of 20A fuses from a local electronics store (Marvac) for $1.50 each (Kragen wanted $4.00 each, Mouser was $1.20 plus shipping, and some Hong Kong eBay reseller wanted only $0.60 each plus shipping, but I was impatient).

The battery feeds fuse 15 directly. The output of fuse 15 goes to connector C3 pin 22 of the PCM and to the common contact of the switch side of the ASD relay socket (pin 38). So, the first thing to try was to remove connector C3 from the PCM (black connector furthest from the firewall) and remove the ASD relay to verify that fuse 15 would not blow with these two removed. I tried starting the car (once click of the key at a time, checking the fuse after each click) and the fuse survived. Now I can focus on the output side of the relay.

The output side of the ASD relay switch socket (pin 30) goes to several places. It feeds the left and right downstream oxygen sensors via fuse 1 and directly feeds the left and right upstream oxygen sensors, the left and right ignition coil packs, and connector C1 pin 12 of the PCM.

I checked impedance from pin 30 of the ASD relay socket in the power distribution center to ground and found it to be a dead short (after compensating for the impedance of my test leads). I was hoping there was not some active component somehow fooling me, but decided to start disconnecting every potential load, one at a time, in hopes that I could eventually make the short go away.

I started by removing fuse 1 going to the downstream oxygen sensors but the short remained.

I then unplugged connector C1 from the PCM (the gray plug closest to the firewall), but the short remained. I was glad the short was not due to the PCM!

Next, I opened up the lower one of the two large wiring harness connectors mounted to the inside of the left wheel well. This connector has the ASD output wire in it (dark green with orange stripe) and appears to probably feed at least the left and right upstream oxygen sensors. I don't have a wiring harness diagram so I'm shooting in the dark a little. Upon disconnection, the impedance of the ASD relay socket pin 30 to ground went to an open circuit, so now I knew the short was downstream from this connector. I re-attached the connector and verified that the short was back.

Next I opened the connector closest to the left upstream oxygen sensor, but the short remained.

Finally, I decided to open the connector closest to the right upstream oxygen sensor but found someone had zip-tied the connector shut. I inspected the wires feeding the connector and found that they were all very close to a thick black plate to which the engine mount was bolted. In fact, one of the wires was kind of "stuck" to the edge of the black plate. I had to exert a little bit of force to "unstick" the wire from the plate. Upon closer inspection, I noticed that the insulation was compromised and that the wire had either been rubbing against the plate or the plate had gotten warm enough to melt through the insulation. A tiny amount of exposed copper wire was shorting to the black place (which was grounded).

I again measured the impedance from ASD relay socket pin 30 to ground and found it had jumped to 2.3 ohms. This wasn't an impressive jump, but 12V/2.3ohms = 5A so 2.3 ohms is a valid impedance hanging off of a 20A fuse. I suppose the ASD input at the oxygen sensors could be a very low impedance. In any event, I was expecting a much higher impedance and was concerned that I may not have really found the problem. In fact, if I'd seen 2.3 ohms to begin with, I probably would have thought I had a problem (when in fact, I would not have, as you'll see).

I proceeded to put everything back that I'd taken out and ensure all connectors were fastened and then turned the key one click at a time, checking fuse 15 after every click to see if it was still intact. I finally turned the car over and it started instantly with a nice loud growl; very very exciting to hear that again after more than a month!

I had to stop and reflect on just how many things are actually required to be operational just to start a car these days, and just how many thousands of little things happen between the time we turn the key and the car actually starts. Cars are truly complex these days and it is incredible how a tiny nick in the insulation of a single electrical wire can keep fuel and spark from being delivered; and can force your fan motor to stay on due to the PCM being shut down in the middle of driving. The symptoms from such a failure can truly be bewildering. I am incredibly lucky this did not happen while on the way home from Vegas, or on the track. It makes one wonder why things like this don't happen more often, and makes one afraid they will.

Hints: The ASD pin designations above always refer to the pin numbers stamped into the surface of the power distribution center, not the pin numbers on the relay body. Steve told me that the ASD output wire is dark green with an orange stripe (confirmed in the schematics) and to look for this in order to follow the ASD output circuit since it goes so many places; this proved to be a helpful hint when tracing the wiring harness.

Finally, thanks to all who helped me out, especially Jack! I hope this helps someone else in the future.

Last edited by Ken Alker; April 24th, 2009 at 01:44 AM. Reason: redundancy fixed
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Old April 24th, 2009, 02:14 AM   #17
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Good job! Now you know your car that much better.

Wait until you get your service manual, it has excellent explanations on which circuits do what, and sometimes why (or at least in theory). It IS a life saver! BTW, the GEN II viper is pretty basic in engine management aspect, if you've ever worked on a late model GM, they have like 10 billion sensors and are much more sophisticated.

If your ODBII output gave you a code you can post it

OR you can:

1. Cycle the ignition key on - off - on - off - on (within 5 seconds)
2. count the number of times the check engine light flashes on and off. The number of flashes represents the trouble code. There is a slight pause between the flashes representing the first and second digits of the code. Longer pauses separate individual two digit trouble codes.

Then we can look it up in the book. But in the mid-late 90's the trouble codes are fairly primitive and only have about 50 or so combination. But hey, makes it awesome for mods without things complaining a lot
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