What could be the source of my reduced engine power warning

Tiny
MTBUTTS
  • MEMBER
  • 2003 CHEVROLET TAHOE
  • 200,000 MILES
I have an 03 Chevy Tahoe, 5.3L V8. I am getting the error P1516 Reduced Engine Power. I have taken it to several shops. Most recently they replaced a modulator that is located in front of the driver, bolted up against the frame closest to the driver. I never suspected this part, but he wanted to try it. I advised them to check the G103 Ground Wire as stated in the TSB for this issue. They said they bypassed that ground by grounding somewhere else, and that wasn't the issue. On diagnostic check he said the TPS and TAC were showing no discrepancies when he was able to duplicate the Reduced Engine Power. Now he wants to replace both sensors and the throttle body. I think this is a waste of time, but I don't have another solution. The problem only presents in the morning. After stopping and restarting 5 or 6 times it will let you drive it the rest of the day. I believe this is because the computer is set to test the data sets when the car goes from 40 degrees F to some magic number. I really am not mechanically skilled at all, but I know a little. Any advice is appreciated.
Monday, September 24th, 2012 AT 12:44 PM

13 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
A) Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing. The wiring for this and the throttle body quite often causes problems.

B) Verify that the starting and charging systems are operating properly. Low system voltage can cause this DTC to set.

C) When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing an individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture
Info.
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Monday, September 24th, 2012 AT 1:01 PM
Tiny
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The mechanic wants to replace the TAC and TPS and Throttle Body. Is that going to fix anything if the problem is with the wiring? The same connectors would still be used for the new parts I assume. Why would it only present in the morning? (Hard to assess I know)
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Monday, September 24th, 2012 AT 1:33 PM
Tiny
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They might or might not and there are many cases whereby replacement of parts did not help. This is more likely to be an electrical problem and I would suggest checking the wirings first.

It can only occur in the morning because of temperature difference, charging system problem or electrical conductivity and any wrong voltage would cause the code.

If you have a scan tool to monitor the TPS and TAC wiring circuit voltages, that would help identify the problem.

If your mechanicswants to replace the parts, would they take them back if it does not work?
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Monday, September 24th, 2012 AT 1:53 PM
Tiny
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I guess I need to ask him. When I dropped it off I assumed he was going to charge me a flat fee to diagnose. Instead when I picked it up he advised me he had about $175 in it, and the problem still isn't fixed. I don't really want to have him keep "trying" things while I am paying for it by the hour. He replaced the one modulator with a junk yard part, and it didn't fix it, so I am wondering if I should have him put the old one back in. I really don't know how to diagnose the wiring problem. He said when he has it hooked up to the scan tool, and he duplicates the error message, there are no discrepancies in the wiring.
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Monday, September 24th, 2012 AT 2:09 PM
Tiny
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If he is not sure and keeps changing components, he should take them back when replaced components do not solve the problem. Junk yards do accept parts return.

For the wiring problem check all connectors for cleanliness and secure contacts when connected. Ten year old wirings sometimes have increased resistance when terminal crimps deteriorate and these can cause problems as control modules are rather sensitive to minor voltage changes.
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Monday, September 24th, 2012 AT 4:05 PM
Tiny
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I just talked to the mechanic and expressed my concern over the wiring harness. He said that the new ground he put in coming off the TAC would mitigate any circuit issue caused by the wiring harness. He is still insisting that the TB and Accelerator Pedal Positioning Sensor should be changed together.
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Monday, September 24th, 2012 AT 4:10 PM
Tiny
KHLOW2008
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He is the one doing the job so I can't argue with that as I am not sure of his findings.
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Monday, September 24th, 2012 AT 4:34 PM
Tiny
MTBUTTS
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Can you answer one more question? Where is the APP Sensor on the 03 Tahoe 5.3L Z-Flex with adjustable pedals? There is a wiring harness and sensor to the left of the brake pedal on the firewall, but I don't see anything attached to the gas pedal that looks like a sensor. I can't find a diagram, as the Haynes manual just gives a written description. Thanks for your time. I can add a photo if that would help.
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Monday, September 24th, 2012 AT 9:19 PM
Tiny
KHLOW2008
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See Diagram.
Image (Click to make bigger)
Thumb
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Monday, September 24th, 2012 AT 9:43 PM
Tiny
MTBUTTS
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Thanks, much appreciated. One part, or can you replace just the sensor?
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Monday, September 24th, 2012 AT 10:04 PM
Tiny
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  • MECHANIC
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Just the sensor.
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Monday, September 24th, 2012 AT 10:52 PM
Tiny
MTBUTTS
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Ok, you're the first person to tell me I can replace just the sensor (Don't get me wrong, I'm happy about that). Any suggestions on how to go about that or what part I need? When I search for parts, even by VIN number it shows I have a TPS (which I don't). The mech and the dealership is telling me it is one piece, and I can't get it separately, but I have a hard time buying that. Any input is appreciated. Thanks for your time.
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Tuesday, September 25th, 2012 AT 1:18 AM
Tiny
KHLOW2008
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The trouble code is caused by the TAC and actually I don't understand why the mechanic insists on replacing the APP as well.

TAC and throttle body is one piece but the APP is a separate item at a different location. Are you sure you got it right?
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Tuesday, September 25th, 2012 AT 7:43 AM

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