P1351 after replacing ignition coil and icm

drakon543

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i hated having someone touch my 97 and my 94 in this regards because so few people actually know how to do it properly. had a shop do my 97 once after the 3rd distributor died and they fought and fought it. fixed it in 15 min when i got home after they tried to tell me the same crap. its definitely hard to diagnose without actually being there i can only go with experience from my 97. p1345 i only got when my timing was off. p1351 i only got when i was having an issue with the icm and wiring. but again not every issue will be identical so keep us posted and we will keep trying to help.
 
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doncaruana

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i hated having someone touch my 97 and my 94 in this regards because so few people actually know how to do it properly. had a shop do my 97 once after the 3rd distributor died and they fought and fought it. fixed it in 15 min when i got home after they tried to tell me the same crap. its definitely hard to diagnose without actually being there i can only go with experience from my 97. p1345 i only got when my timing was off. p1351 i only got when i was having an issue with the icm and wiring. but again not every issue will be identical so keep us posted and we will keep trying to help.
Thanks and glad I'm not alone!!! Gonna be warm tomorrow and I have a bit of a break from work so I'm going to run down those wires. One thing that I'm a bit confused on is exactly what "ICM" stands for. I thought it was "Ignition Control Module", which is a newly installed AC Delco. But the troubleshooting guide keeps referencing "ignition coil module", yet the diagram also says "Ignition Control Module". Which leaves me completely confused at to which is which...
 

drakon543

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Thanks and glad I'm not alone!!! Gonna be warm tomorrow and I have a bit of a break from work so I'm going to run down those wires. One thing that I'm a bit confused on is exactly what "ICM" stands for. I thought it was "Ignition Control Module", which is a newly installed AC Delco. But the troubleshooting guide keeps referencing "ignition coil module", yet the diagram also says "Ignition Control Module". Which leaves me completely confused at to which is which...
either or tomAto <> tomato
like my wifes stupid dodge journey oil filter housing or oil filter adapter same thing just who are you talking to.
 
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doncaruana

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A little extra help here - apologize if these are dumb questions... Below is the wiring diagram from the P1351 troubleshooting.

Step 6 says to "Check for a faulty VCM connection." (Similarly Step 13 says "Check for a faulty ignition coil module connection.")
What exactly does that mean? Is this the "jiggle the wire" thing?

Step 9 says:
  1. Connect a test lamp to B+.
  2. Probe the ignition coil module harness connector terminal C.
What is B+ here? I can see from the test that it is to check that C has a good connection to ground (BLK/WHT 451), I just don't know where B+ would be to validate that. Is it the positive terminal on the battery?

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exp500

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Step 6 is disconnect computer plugs and inspect- Warning 50 mile drive cycle and crankshaft relearn if disconnected. If you wiggle the ICM/Coil connector wires and it misses, it usually is very near the ICM or coil in the loop of wire. Last 6 inches, flex just that area next. If it misses again you could probably narrow it down to the inch.Replace a long amount, where you can reach and hide splice. The computer will relearn on its own if you disconnect, but trans shifting and everything will be a little different while learning. Use Dielectric grease on the plugs and gaskets, coil and ICM connectors.
 
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doncaruana

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Step 6 is disconnect computer plugs and inspect- Warning 50 mile drive cycle and crankshaft relearn if disconnected. If you wiggle the ICM/Coil connector wires and it misses, it usually is very near the ICM or coil in the loop of wire. Last 6 inches, flex just that area next. If it misses again you could probably narrow it down to the inch.Replace a long amount, where you can reach and hide splice. The computer will relearn on its own if you disconnect, but trans shifting and everything will be a little different while learning. Use Dielectric grease on the plugs and gaskets, coil and ICM connectors.
So of course now I'm a little worried. Lol. In step 4 it says to disconnect the Grey connector from the vcm and then check the wire that goes to the icm. You're saying once I disconnect that, it's going to make it need to relearn etc? Just the process of disconnecting it won't mess anything up right?
 

exp500

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Me, I would wait to disconnect that. If it passes ICM/Coil wiggle tests, change coil. If it still shows P1351 then disconnect battery and unplug computer. I do not like sparks jumping around computers. Some may disagree.

If It is still showing P1351 after cleaning computer plugs, the next step is to splice a new wire into harness. You need pin removers, new Pin(s), crimpers (specialized). Your mechanic may have them, or Get info from dealer GM or service manual. See Here-https://www.tahoeyukonforum.com/threads/helpful-links.131971/

Another useful test- Multimeter on Ohms, connect red to Bat-, Black to firewall ground, eng ground, and all the grounds you can see and reach. Hi resistance will cause that voltage spike you are getting.
 
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doncaruana

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Well, given what led up to the issue, I decided to "work backward" and leave the VCM the hell alone unless I had to!! Got a $4 test light from Harbor Freight and checked the ground on connector C on the ICM plug - worked fine. Then I flipped the other side of the probe and put it on ground and checked the two outside connectors on the ICM plug (A, pink, is 12v and D, white/black goes to the coil). One of them lit up and the other didn't. Aha! Now, if I was a lot smarter, I would have made an immediate note of which one didn't light up...but I didn't. :( Because you can guess what happened next - I couldn't duplicate it. Took it on and off a couple of times and even tried jiggling it a bit but both lit up each time. I put it back on and made sure it was in there snug and put everything back together and tried a couple of test starts successfully.

So I know it's one of those wires and my mechanic suggested trying to replace the connector (get one from a junk yard) first before chasing the wires and I think that's a decent idea. Regardless I feel a lot better about the root cause at this point. Or I could buy a new ACDelco from Amazon ($36) or Standard Motor from Oreilly or Duralast from Autozone (both $29) .

Any other suggestions from anyone?
 
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