04 Yukon Denali CEL Codes Galore

[04YukonAWD]

Hey guys I have a 2004 GMC Yukon Denali that has the dreaded Reduce Engine Power message on along with the CEL T/C light.

As I carry a obd2 scanner i checked the codes and have 4 codes,
P2135 P0120 P0220 P1516.

I am lost here on what to check. I switched throttle bodies from a silverado and that did not fix the issue. What has me more stumped is that when I erase the codes with the engine not running as soon as the scanner erases them the codes pop up right that instant.

Seems like its not reading whatever it has to read before the engine turns over.

 

[about20ninj45]

Hey guys I have a 2004 GMC Yukon Denali that has the dreaded Reduce Engine Power message on along with the CEL T/C light.

As I carry a obd2 scanner i checked the codes and have 4 codes,
P2135 P0120 P0220 P1516.

I am lost here on what to check. I switched throttle bodies from a silverado and that did not fix the issue. What has me more stumped is that when I erase the codes with the engine not running as soon as the scanner erases them the codes pop up right that instant.

Seems like its not reading whatever it has to read before the engine turns over.

It may be worth the effort of unplugging the truck battery for about 15 min to let all the electricity drain, that way you can clear those codes that are sticking for some reason.

 

[04YukonAWD]

Sounds like its worth a try. I have also done the wiggle test with no wires feeling loose or have any play either.

It may be worth the effort of unplugging the truck battery for about 15 min to let all the electricity drain, that way you can clear those codes that are sticking for some reason.

 

[about20ninj45]

Sounds like its worth a try. I have also done the wiggle test with no wires feeling loose or have any play either.

You may have a bad tps. Did you also check the butterfly in the throttle body to see if it opened all the way and returned properly with no corrosion? You may need a friend to help, but if one of you guys step on the pedal and the other check the voltage on the throttle position sensor, you should see a viltage change ( up to 5 volts at wide open throttle ) ... if not then you know its the problem, and its causing the other codes to pop up.

Get access to a multimeter and a scope if you can

 

[04YukonAWD]

Yesterday I swapped throttle bodies from a 05 Silverado to the yukon and the problem was still there. The throttle butterfly opens and closes freely and also moves when it clicks right before starting the engine.

My guess is that it maybe the accelerator pedal of some sort.

With a test light I checked the wires on the throttle body connector on the plug itself and before the connector and all have continuity.

 

[about20ninj45]

Yesterday I swapped throttle bodies from a 05 Silverado to the yukon and the problem was still there. The throttle butterfly opens and closes freely and also moves when it clicks right before starting the engine.

My guess is that it maybe the accelerator pedal of some sort.

With a test light I checked the wires on the throttle body connector on the plug itself and before the connector and all have continuity.

Your not checking for continuity, you want to see voltage rise and fall on the throttle positioning sensor. There is a sensor on the tb itself and there one attacthed to the firewall right coming out near the pedal.

 

[04YukonAWD]

Got home after 2hrs of having the battery disconnected and CEL and Reduce Engine Power are still there.

---------- Post added at 08:59 PM ---------- Previous post was at 08:57 PM ----------

Got it. I will check the voltage with the multimeter and check each pin. What am I suppose to get across the board 5v?

Your not checking for continuity, you want to see voltage rise and fall on the throttle positioning sensor. There is a sensor on the tb itself and there one attacthed to the firewall right coming out near the pedal.

 

[Yukon Lover]

Yes I believe your looking for 5v change max at wot, a lot of people have had this problem, including myself, your going to have to check the sensor on the pedal the sensor on the throttle body and the tac module that should be on the driver side firewall and any and all wiring, some have found it to be just a broken wire, I think the yellow on the throttle body harness near the connector, sometimes it gets brittle. Good luck.

 

[04YukonAWD]

I really do hope its something simple as a wire or at most the pedal sensor. I will check the pedal sensor and harness first since that would be a start.

Yes I believe your looking for 5v change max at wot, a lot of people have had this problem, including myself, your going to have to check the sensor on the pedal the sensor on the throttle body and the tac module that should be on the driver side firewall and any and all wiring, some have found it to be just a broken wire, I think the yellow on the throttle body harness near the connector, sometimes it gets brittle. Good luck.

 

[Yukon Lover]

Ya we all hope it's something that simple but it never seems to work out, start there and work your way out, the pedal sensor, the harness to the tac, the tac, the harness out to the throttle body, and the sensor on the throttle body, also you could check and clean the 3 grounds, one is under the radiator drivers side, second is on the side of the block drivers side, and the third is a pain in the ass to get at, it's on the back of the engine drivers side, I believe it's bolted to the back of the cylinder head