First time got a code p1351. Changed out the ICM with a cheap one from 1aAuto, and wouldn't run, so put my old one back on and ran. Then changed coil and new ICM, runs ok, but code came back ??? I know that this is : "high voltage in the Ign. circuit" but not sure why it would suddenly appear ?? Car is a bone stock Base 96 with about 117K miles.

 

Cleaned all grounds, and will see if code returns. Found a bad + battery cable not sure if that would cause this code, will take a ride tomorrow & see.

 

Still chasing this P1351 problem, and have been on various LT1 Forums. Sometimes, fix is simple as a broken wire, or replace the ICM...not so, mine. Fuse 25 is good, and getting 12v at the fuse socket with key on. blk/wht wire at the ICM plug tests good for ground. Will test the others later.

I have changed a lot of stuff on this 96, chasing a "lope" in open loop, and think this code emerged after I changed the Engine Coolant Temperature sensor, and am now looking for a schematic for the 2 wires to the temp sensor.

 

All the explanations for P1351 says the ICM or the wiring or the wiring connectors/connections. Have done resistance/continuity checks of each wire on ICM harness? Also test wiring from ICM to PCM.

 

Yeah, you're right about connections, etc. checked all of them except the white one from the PCM, need to test while cranking. The ICM connector has 4 wires, the white/black goes to ground and checks fine. The pink and dark green both have 12v with the key on. According to what I have learned, P1351 indicates that ICM input (white wire) from the PCM stays above 4vdc during cranking, and sets a code ??

The car starts and runs, so the Service Manual says to do a : Powertrain OBD System Check. Not at all sure what is going on with this thing. Been throwing parts at it for almost a year not, trying to correct a "miss/lope" in open loop, and now this ???

 

Opens inside the wiring can be intermittent and difficult unless you have a good cable to substitute with. But replacing parts is not the way to troubleshoot or diagnose.

BTW P1351 can also be low voltage. But some books say just Ignition Coil Control Circuit - High Voltage. That means it's measuring a bad (high) voltage so that would be on the White wire to the PCM and that means that wire is not an open. There are are only 3 more wires on the ICM (4 total). You have the power feed which you say is good. Next is the ground wire - should be easy to test but I would do it all the way from the battery. Last is the coil driving dark green wire to the coil. Well this could mean a bad coil then also. I'm assuming you replaced that also by know? Is so look over the wire harness and connectors again testing them for continuity. I really think the problem is in those items - ICM, wire harness/connectors or even the coil. If not then worse case would be PCM though they are fairly rugged but you do have a open loop issue also.

Good luck.

 

Kinda thinking it is "intermittent" seeing as how I have good ground and green and pink are "hot" when I test them with the key on. So going to look closer at that. Also, the thing starts up and runs. When I first got the P1351, I changed the coil and ICM. First ICM new part I installed was defective, and would hardly run. One of the first things I did was remove the battery and clean the grounds, also G107 at the bellhousing, cleaned that ground. The neg. battery cable also goes to the bellhousing, and there is a wire from the ground cable that grounds to the frame, about a 10ga. Also, is a braided ground from the frame to the bellhousing, cleaned both ends of that as well as installed another braided ground from the frame to the engine while I was under there.

I have been searching forums including LT1, and this code on Camaros , roadmasters, etc. and most just replace a part, and yahoo---fixed. One guy with a Camaro, had no power to Green, replaced the wire and everything good ( assume the car wasn't running before, didn't say ??)

My book says: DTC P1361 Ignition Control (IC) circuit low voltage (shorted or grounded circuit) Condition to set: PCM detects 84 revolutions of the crank with no IC activity "not running, I guess ??"
DTC P1351 Ignition Control (IC) circuit High Voltage ( open circuit) condition to set: PCM detects voltage on IC Circuit in excess of 4.6 volts....not sure I understand that seeing as how Pink and Green are 12, how does the White wire from the PCM get in excess of 4.6 when cranking ?? So, still looking

 

OK that IC circuit low voltage must be mis-printed in my book as it's used for both IC voltage high and low P1351.

I really think if you have an intermittent problem it's an intermittent connection. Wire or connector. Only 4 wires and 2 parts - ICM and coil. Myself I would take some long meter leads and measure resistance from the black/white wire at the ICM all the way to battery negative.

 

Thanks for the response, decided I better get back and wrap up this thread. Not sure if I fixed the problem, but the code is now gone after several key cycles, not sure if it will stay off until I take a long drive.

I changed the connectors on the Coil and ICM, after peeling the wires back. I checked voltage from the PCM (white wire) while cranking and was about 1.8V, and traced the pink wire from the coil and ICM back until I found the "splice", and this tested good for 12V. The green wire is just a loop from the coil to the ICM. I traced the black/white (ground) wire back, and soldered another wire to it and grounded to the engine, so definitely good ground. So, those 4 wires are good.

I ran down thru the Diagnostic Table (Tree), and that involved ensuring power and grounds as well as the white wire from the PCM, setting the code P1351 showing excess voltage, and the Table indicates that if the engine runs, then "scan" to find the cause. I guess I just don't understand what would allow the PCM to send "excess" voltage to the ICM via the white wire ?? Can only imagine it must have to be set by the Opti

Might be one of the connectors was faulty ?? Hope it is cured...thanks for the input

 

Well, Code P1351 reappeared and I think it is being set by the opti/fuel pump. When I turn the key on, it primes for 2 seconds as it should. If I leave the key on, the it has to crank for 3-4 seconds before it will start. I believe that this is because it is waiting for the oil pressure to reach 4psi then it activates the fuel pump again, and starts. If I go immediately to start, within the 2 second frame, then it starts right up ??

I understand that the ECM needs to receive a pulse ( high or low, not sure) from the opti, telling the ECM " hey, I'm crankin, turn the fuel pump on ". Otherwise, it has to wait til the oil pressure switch overides and activates the fuel pump relay ?? Anyone know about OPTI PULSES, etc ?????

 

Hi CardoO. Figured I would follow up and let you know that I think I have cured the P1351 issue. It was the ICM, and it was also causing the engine to "lope" at idle. I took my old OEM and recently installed Delphi ICM's to Autozone and had them tested, and both failed. I had them test one of their new ones, bought it, installed, and the car runs great for the first time since I bought it over a year ago. I believe the previous owner was chasing the same problem, as he had replaced a bunch of parts as well as having had the PCM rebuilt. I never imagined a bad ICM would cause such symptoms, and you sure never suspect after replacing with a new Delphi. Thanks for your input and assistance.

 

I am having a similar issue, I did put a new Icm and coil and it runs good but the p1351 code won’t go away, what Icm should I use?