P106c ?

[a5150nut]

2006 GMC K3500 LBZ


Changed GPC today and now have a P106C code. Research tells me I now have to reprogram the GPC with injector values. How is this done?

Is there a Learn process for the GPC?


What was a quick 15 minute fix has turned into. . . . . .

[DmaxMaverick]

It should catch the values during startup diagnostics. Sometimes it takes several cycles, and occasionally requires a scanner to initiate the diag. if it doesn't happen soon enough (such as for an emission test in CA). If the GPC is replaced at a dealership, normal procedure suggests manual initiation after the install, but also mentions it will occur "eventually" if it isn't done. It doesn't specify if it is unique to CA emission systems or not so, YMMV, as usual. If you aren't OCD about it, either ignore the lamp or cover it for a couple days. If it's still there, you'll need to initiate the diag. I've not done it, but I've heard you can do a system "reset" to get it to register. A "reset" is simply disconnecting both batteries and grounding one of the cables to chassis for half an hour.

[a5150nut]

Thanks DmaxMaveric



Its not a Ca truck and Im in Tennessee so no checks.


I wasn't sure so just put the old one back on. Looks like it was just rehearsal for me then. I will try the new one again and disconnect the batteries this time. Had to do that on my wifes Jeep to get a pesky code to clear. I cleared with scanner but it came right back, until disconnecting the battery.

[DmaxMaverick]

The CA emissions may not be an issue, but that's what I have to deal with, and sometimes it matters, even on fed emission trucks.

Just disconnecting the batteries can take up to 24 hours to reset. Grounding a Batt+ cable expedites that to about 1/2 hour. On most GM vehicles anyway, in my experience. I go through this mess every 2 years on every vehicle I have registered, having to smog test. There's always some PID that didn't run, and I have to burn gas/fuel to get them to run (even on a PHEV). It's stupid, but we have to deal with it to live in the lap of luxury in the land of all things righteous. Good luck with it.

[a5150nut]

Re installed it today. Disconnected batteries for an hour. Cleared codes then took it for a test drive. Dang light is back on. Cleared codes again. Still no joy. Will give it a few days to see what works out.

[a5150nut]

Had some time today so I disconnected both batteries and used jumper cables to ground positive leads to engine. Left them hooked up for a couple hours. Just retried again and cleared codes before starting.
I now have two codes. Both P106c, one pending, one stored. And still that damn light!
I clear them and code reader says cleared. Then next read and there they are.

[DmaxMaverick]

If the code immediately returns after the battery disconnect, it is a current active condition.

I didn't look up the code until now, and I'm not even finding it. Are you sure it's related to the GPC? The PCM needs to recognize the GPC and the plug feedback voltages, but I don't recall the codes from before, or if we pulled them. It just wasn't an issue. If you have an alldatadiy account for your truck, it should be easy enough to run down the DTC flowchart.

[a5150nut]

What I have come up with is the GPC was not programed with injection rates. You previously said disconnecting and grounding the B + cable would force a re-learn to correct this or after driving for a while it would learn rates. I have made a few trips around town maybe a long highway drive is needed.


At least i don't get Number 4 glow plug bad any more.

[DmaxMaverick]

I don't think it's the "injection rates" it's reading, or trying to read or associate. I'm not finding any reference to that, and it should make no difference, functionally. The GPC must be able to relay the resistance and feedback voltage for each plug, though.

Did you replace #4 GP? Others? If not, it could still be an issue, or wasn't the exact issue from before. What was the reason for replacing the GPC? Have you tried reinstalling the old one?

I'm curious to know what the service manual has to say about this DTC (not curious enough to pay for a manual subscription for a truck I don't have or work on). A thorough web search shows the only folks talking/talked about P106C in regards to a GM truck is you and me. The only other reference to it is older foreign cars with tranny issues on foreign websites, and even they are vague with no positive solutions.

[a5150nut]

Yes I did replace #4 GP twice. No GP fault with new GPC just P106c. When I put the old GPC back in i get fault #4 GP no P106c. The reason for new controller was re occurring fault on #4 GP.



I had found a thread on the diagnostics that said multiple fails on a GP after replacing was harness or controller. Checked voltage to verify harness so next step was controller.



I found a thread on another site said the GPC stores a backup of injection rates and that is what causes the P106c, its looking for the stored codes. So if it doesn't re learn and can't be forced to I'm looking at a trip to the dealer to have force fed. Just don't have the $$ for that right now.

[DmaxMaverick]

OK. I got access to the service manual. DTC P106C is a ghost. It doesn't exist in the real world. You were correct replacing the GPC for the GP failure repeat, exactly what the manual suggests. The bad news is, if the PCM complains after a GPC replacement (such as a recurring code that won't clear), you must use a Tech II to run the fuel injector flow rate program, so the PCM and GPCM can adjust GP voltage for individual cylinders (I think it isn't really that, but the module needs to "pair" with the PCM). The manual doesn't state what happens when it's needed and you don't, so now we know. Either tolerate the MIL (it may clear itself, eventually), or pony up for some shop time. It shouldn't effect drivability in any way, so there's no hurry. One other interesting thing I noticed is, only the OEM replacement controller module shows a statement suggesting any programming. None of the aftermarket controllers do. Not sure what it means, but all the controllers I replaced before were aftermarket.

[a5150nut]

OK. I got access to the service manual. DTC P106C is a ghost. It doesn't exist in the real world. You were correct replacing the GPC for the GP failure repeat, exactly what the manual suggests. The bad news is, if the PCM complains after a GPC replacement (such as a recurring code that won't clear), you must use a Tech II to run the fuel injector flow rate program, so the PCM and GPCM can adjust GP voltage for individual cylinders (I think it isn't really that, but the module needs to "pair" with the PCM). The manual doesn't state what happens when it's needed and you don't, so now we know. Either tolerate the MIL (it may clear itself, eventually), or pony up for some shop time. It shouldn't effect drivability in any way, so there's no hurry. One other interesting thing I noticed is, only the OEM replacement controller module shows a statement suggesting any programming. None of the aftermarket controllers do. Not sure what it means, but all the controllers I replaced before were aftermarket.


Thank you.

[a5150nut]

Found a shop here in Knoxville City Diesel, that understood what I was talking about and they said bring it in. Took him all of 10 minutes to fix the SES light problem. He agreed it takes a Tech 2 to run the relearn program.



Anyone in East Tennessee needing Duramax service I would highly recommend these guys. Andy was quick and accurate first time out.


City Diesel and ask for Andy