GM intermittent Engine Power Reduced

Bashar Instructor Kuwait Posted   Latest  
Unsolved
Driveability
Electrical
2007 Chevrolet Silverado 1500 LTZ 6.0L (Y L76) 4-spd (4L60-E)
P1516
Intermittent Reduced Engine Power

Hi, this truck has an electronic throttle actuator equied with two fully independent TP senaors. 

The trucks drives fine until it randomly sets Reduced Engine Power mode (always at highway speeds), if i shut it off and it will run again perfectly. 

The code is P1516 which is not of great help. So i pulled up my scope to check the TP signals, one of them has dropouts (yellow) the other signal is clean. This applys to the 5V refrences too, the 5V ref for the noisy signal has dropouts too! 

What has been done to get this dropouts resolved:

1-confirmed power/grounds for the control module (load tested) 

2- load tested the wiring going from the model to the TPS 

3- cheked connectors

4- Pluged in new throttle actuator, ( still the same dropouts , so I kept the old throttle) 

5- replaced the throttle module with used one, still i have the dropouts

Help is very appropriated am out of any ideas and going back and forth without any luck! 

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Interesting
Dwight Owner/Technician
California
Dwight
 

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

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Bashar Instructor
Kuwait
Bashar
 

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

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Paul Diagnostician
Tennessee
Paul
 

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.

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Helpful
Matthew Technician
Nova Scotia
Matthew
 

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.

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Bashar Instructor
Kuwait
Bashar
 

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

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Matthew Technician
Nova Scotia
Matthew
 

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.

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Bashar Instructor
Kuwait
Bashar
 

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

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Gary Owner/Technician
Colorado
Gary
 

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…

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Bashar Instructor
Kuwait
Bashar
 

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

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Paul Mechanic
Illinois
Paul
 

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…

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Bashar Instructor
Kuwait
Bashar
 

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

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Ray Diagnostician
Ontario
Ray
   

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

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Bashar Instructor
Kuwait
Bashar
 

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

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Victor Mobile Technician
California
Victor
 

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

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Bashar Instructor
Kuwait
Bashar
 

I have de-pinned the connector check it thoroughly

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Interesting
Victor Mobile Technician
California
Victor
 

Have check for tsb's?

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Edgar Owner/Technician
Illinois
Edgar
 

Check and clean your grounds specially g102

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Robert Owner/Technician
New York
Robert
 

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.

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Bashar Instructor
Kuwait
Bashar
 

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…

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John Owner/Technician
Iowa
John
 

There is a bulletin for that code. HTH

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