Code P0356 - again *%$#@

[Fredk20716]

Hello All –

Chasing gremlins again! My check engine light is on and the Code scanner shows P0356. So this is what I have done so far (n ot in order):

1-Flipped ignition coil with another one that knew worked
2- Replaced #6 ignition coil with new coil
3- Replaced #6 spark plug
4-Replaced #6 plug wire
5-Replaced PCM (based on repair shop stating hard drive was dead).

I have done what I can to this point and am out of next steps to take. The engine runs smooth and has plenty of pep. Clearing the codes will last as long as the engine is running however when I shut it down and on restart the check engine light comes on and code scans as P0356 again. What should I be looking for? Visual inspection of wiring does not show any problems such as chaffed or loose wires.

[Jim_HiTek]

Seems as though that code is so generic that it's little help in isolating a problem. It's also often points to an issue that is specific to the manufacturer and they'll be the experts on what it most likely is causing it

Here's a listing of 'probable' causes, seems like you've already tested for most, if not all of them:

Faulty or corroded wiring of second cylinder coil pack
Faulty ignition coil(s)
Faulty spark plug(s)
Faulty idle air control valve or electronic body
Damaged or corrosion in the wiring that connects second cylinder coil pack to the PCM
Open or short in the wiring or electrical circuit of second cylinder coil pack
Carbon buildup causing blockage in the Throttle Body air passages
Intake manifold vacuum leaks
Faulty PCM (rare)

Perhaps you could join a Vortec forum and ask your question there?

Don't know if you've seen this web page but maybe there's something there that could help? The video might be an aid too...Code P0356

Good luck! Hope you find the cure soon.

[Fredk20716]

UPDATE; It looks like the problem has been solved. I swapped out all 8 plugs and plug wires and the code disappeared (actually disappeared after install on cylinders 2-4-6-8). Removed the Denso TJ14R-P15 and replaced with AC-Delco 41-101. It appears the Denso are not the best plugs for a Workhorse with a GM 8100 engine according to all the RV forums. I’m not sure how long ago they were changed out but they were chipped and fowled. I also replaced what appears to be the original AC Delco plug wires with Ultra-Power Magnum SPW8100 plugs. No more Check Engine OR Service Engine Soon light or the P0356 code.

Keeping my fingers crossed!