P2101 and P1516 Issues w/ GMPP 376/480 ECM

Hey All,

I have a customer with a 1978 TA with a 6.0 G8 engine with the LS3 heads and intake. The cam is a 226/232 114 and it is a TKO 5 speed trans.

The controller, harness and accel pedal are all the kit from GM for the 376/480 engine. They used the supplied MAF and mount and it is in a 4" tube with about 6" of straight tubing before and after the sensor.

Everything is great as far as start up, idle, cruise and even WOT power. The issue is that 75% of the time it will go into a reduced power mode and only happens under heavy load (90-100% throttle approx) and run up into the higher RPM's. After the run and while it is barely idling in the limp mode, you check for DTC's and both the P1516 and P2101 are stored. Clear the codes while it is running and it goes back to running normal instantly.

Initially I opened up all the airflow diagnostic tables and still would go into a limp mode. I then tuned off the P1516 and P2101 codes in the DTC tables (both to SES Enable Off and Error Mode 3-No Error Reported) and on the first dyno run with these settings, no codes and runs well after. Did a second run a short time later with no ECM changes and again goes into limp mode.

I then had a known good TB off of a 2007 Z06 and did two back to back dyno runs, no codes and runs well, for now. After a long drive with no WOT, still good to go. One WOT run and back into limp mode. The limp mode and codes always happen as the accel pedal is released, not under load.

My customer is going to try another TB just for trying sake. I have done some reading and searching here and some folks have the same issue with no fixes that I can find.

Here is the current tune with the codes off as well as a run where the code set (Dyno4) and one where it did not (Dyno3).

Let me know what y'all think as this is a new one for me.

Thanks.

Mike Norris

email support with your file and the guys can add the P2101 throttle tolerance parameters to the editor. If you still get P1516 after that then that is a problem because we cannot read/write the TAC module segment that raises P1516.

Usually its' a throttle tolerance issue, generally the cal allows 6-8% error on the desired throttle position vs. measured position (p2101 is checked by the ECM and P1516 is checked as a backup by the TAC which is a secondary CPU iside the ECM we cannot read/write). If your TPS sensor is a little off center then it can give problems one way and not the other and often you see this on blown cars that put a little more pressure on the throttle blade. You also see this if people are rough on the throttle shaft if they have drilled the thorrle blade, slightly bending it or deforming the throttle blade itself.

Thanks Chris,

I sent the file to support so we shall see. Unfortunately there is no external TPS on the LS2 style TB's and the two TB's I have had on the car were working units totally stock units.

We will see :pray:

Mike Norris

I was wondering if you guys had any update on this and the cause. I have the exact same problem down to a T. Car was built at another shop and I need to get it fixed so they can deliver it.

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Originally Posted by Alvin

I was wondering if you guys had any update on this and the cause. I have the exact same problem down to a T. Car was built at another shop and I need to get it fixed so they can deliver it.

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Are they using the GMPP controller or did they source their own VCM?

Its got a GMPP controller. Thanks. I know they shortened wires and already found two mistakes. I think they need to go back over everything there with a fine tooth comb. I've also had to replace a entire ECM connector on a GMPP harness where a wire clip was broken out of the box. Story is they are made in mexico and not to the same standards as other harnesses.

I have a customer with an 09 G8 gt that isntalled an ls3 TB (stock) and had the same issue. Only 09.5 g8 had the ls3 throttle from the factory. The rest came with ls2 units. The odd thing is I have an 09 as well and installed the ls3 without any issues. The only difference between mine and his car is I maxxed the throttle opening rate on my car and his (different tuner) is not. Im going to try maxxing his table this weekend to see if that eliminates the issue.

I have the same exact issue and I have not seen anyone actually post a resolution.

On my beater truck, 03 silverado i added a ground to the black wire with white stripe in the harness between the tac and the throttle body and never had an issue after that. The truck would come down to an idle and start running on half the cyinders say reduced engine power and die. The truck went completely dead and would crank but no start, started probing the ground wires and had no continuity. Stripped back the insulation and wrapped temporay to get it back to the shop where i soldered the spare ground in permenantly. You have to check though, there may be another issue. I am fighting the same problem now p2101 TB will not operate with key on so its failed at this point.