GM intermittent Engine Power Reduced

I would replace the pigtail to the throttle body and perform an idle learn reset with a capable scan tool.

Thank you Dwight, yes i haven't thought about idle relean as she was idling fine, i have load tasted that bigtail twic.

The dropouts are normal. It is the pcm causing it. It is a circuit check. I would check the ground strap that connects to the firewall on the driver's side above the valve cover. This ground has caused various problems in the past.

I was thinking this as well, I just couldn't remember if it was GM or another make. Rear of the cylinder heads to the firewall.

Wow if these dropouts are normal, then i was going in circles! Yes wherever i power the tac module on bench, it gives clean 5V ref!!! The grounds are fine specially G104 and the strap, spent good time testing them

I agree with Dwight above for the throttle relearn. The condition for setting the P1516 is a correlation problem between the actual and predicted throttle angle for more than .5 of a second.

I assumed that these dropouts would last more than. 5 sec, thus setting the reduced power mode, will do the relearn it might help,

Hello, Bashar. I had a 2003 GMC Yukon with an intermittent code P1516 that drove me crazy for several months. Although I had volt-dropped the battery to engine block ground a number of times, it turned out that the block ground would fail under heavy electrical loads. The engine block ground above the oil pan rail grounds EVERYTHING on the engine. So, don't just look at the ground, take it apart…

Thank you Gary, will take them apart, you are right my 5Amp load testing might not simulate actual road loads especially for an intermittent issues

How dirty was throttle body? I would try cleaning it and retest. I did not look up code definition, but if it is the difference between actual and perceived, it could be blade is not where it should be compared against MAF and map signals at the rpm where it sets. You may have an issue with one of the other sensors. The pcm models the scenario and picks out the most likely suspect. I had an ion…

Hi Paul, it wasn't that dirty and the throttle moves without restrictions, in fact it was my first step cleaning it. regarding MAF i didn't check its readings but will consider

Hello Bashar, this 07 Silverado engine block to the right frame ground strap looked ok but it fell apart when I pulled on it.

Amazing, mine was somehow brittle,all grounds would be removed and rechecked

How 's the connector of the throttle? I have replaced a few because they burn out and don't make good contact and set's the code and messege on instrument cluster

I have de-pinned the connector check it thoroughly

Have check for tsb's?

Check and clean your grounds specially g102

Drop outs are normal pcm function. Wiring harness issues possible. Have you verified voltage at sensor matches displayed voltage on your scan tool? Also be sure to check for excessive ac ripple from a failing alternator.

Yes i have verified the circuit integrity, however, the dropouts can be seen on scope only since OBD referesh rate is slower! The dropouts are there during engine off as well as engine running, also i have tested AC couple and the ripples are fine below 1 Volt so that am sure it is not related to alternator nor secondary circuits! I have done all gounds right now and am waiting to see if the…

There is a bulletin for that code. HTH