NEED HELP Persistent P2138 And Reduced Engine Power

I recently hit 50,000 miles on my '04 Ascender and have had nothing but problems since. I've already cleaned the throttle body, replaced the fan clutch, and tested the APP sensor. The SES and REP lights seem to turn on at random and the only code I'm getting is the same P2138 every time. I tried running it with the fan clutch unplugged before I replaced it and still had the same problem. The new fan clutch also seems to stay locked up after every startup until the engine goes above 4,000 RPM even when cold. I'm thinking that it could be a damaged or corroded wire somewhere but I don't know where to start beyond the harnesses for the fan and throttle body.
 
OP
OP
UsernameIsTaken
I drove around today with a BlueDriver connected and the freeze frame feature caught the CEL and logged all the data it had access to.
  1. DTC that caused freeze frame data: P2138
  2. Fuel System Status: Closed Loop
  3. Calculated Engine Load Value: 100.0%
  4. Engine Coolant Temperature: 94°C, 201°F
  5. Short Term Fuel Trim Bank 1: 1.6%
  6. Long Term Fuel Trim Bank 1: 4.7%
  7. Intake Manifold Absolute Pressure: 81.0kPa, 23.9inHg
  8. Engine RPM: 1561 rpm
  9. Vehicle Speed: 12km/h, 7 MPH
  10. Timing Advance for #1 cylinder: 9.0°
  11. Intake Air Temperature: 51°C, 124°F
  12. Absolute Throttle Position: 34.1%
  13. Commanded Secondary Air Status: 0
 

Mooseman

Moderator
Calculated Engine Load Value: 100.0%
That one is kinda strange since your RPM and throttle don't jive with that.

If you checked all your wiring and your APP sensor is new, then the only thing left is the throttle body itself is defective. The code is saying that what the pedal is asking doesn't match what the throttle is giving. I'd grab one from a junker at a u-pull. Give it a shake test for any noises before taking it out of the yard.
 

TJBaker57

Well-Known Member
If you have the Torque app and it works with your Bluedriver I recently posted a bunch of PIDs that might be helpful.

There are PIDs for the two reference voltages, both accelerator pedal sensors, both throttle sensors and so on. Torque also has data logging capabilities that I find quite useful for such things as this intermittent trouble you have here.

I just recently confirmed these pids worked on a 2018 6.0 V8 Chevrolet Express Cargo Van so I suspect they are widespread. ( I did have to drop my usual '01' at the end of the pid though)20190819_130041.png
 
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MRRSM

Lifetime VIP Supporter
Even though this TSB linked below is for the later Model Trailblazers and Envoys... The Principles involved seem common sense enough to perhaps relate to the Mystery of the Reduced Engine Power Code... and the similarity of symptoms. Please know that the one thing that is missing from this TSB is the suggestion that once you have the Throttle Body removed completely... grasp it well and give it a decent "Shake Test".

Listen carefully adjacent the Solid State Cover that conceals the Throttle Plate Drive Motor Electronics and Plastic Drive gears within. If you can hear anything rattling around inside of the TB... Find an inexpensive replacement at a Salvage Yard. But Remember... Prior to laying down your $$$ on the Counter... give IT a similar "Shake Test" to ensure that IT does not suffer from the same malady of having Stripped or Broken Internal Drive Gears.

One Last Note... On occasion... the Weird Round Notched Throttle Body Gasket can "squash" itself inappropriately when being installed and allow Ambient, Unmetered Air to bypass the usual measurements offered by the MAF/IAT if present ...or alter the MAP Sensor performance... so replacing IT is just as important:

 
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OP
OP
UsernameIsTaken
I returned the new EV fan clutch and replaced it with a new mechanical fan clutch, which should rule out the fan entirely. I also tested the resistance on the throttle body and tried shaking it. The resistance values checked out but it made a slight ticking noise when I shook it that sounds like a gear moving near the connector. I can try switching it with the one from my '04 Rainier and see if it still has the same problem. I also noticed that the reduced engine power happens more frequently when the truck is warmed up or when the A/C is on. Is there anything else on the 5V circuit that could be acting up?
 

Mooseman

Moderator
You'd have to look up the schematics in the manual as the fan is a usual suspect when the 5v is acting up.

Swapping the TB is the easiest and quickest way to rule it out (or confirm it) as defective.
 

MRRSM

Lifetime VIP Supporter
You can Download a Complete, Digital GM OEM Service Manual for your specific GMT-360 SUV at the Link below (Courtesy the work of @Moosman in archiving these Invaluable Resources):

 
OP
OP
UsernameIsTaken
I swapped the throttle body from my Rainier onto the Ascender and I got reduced engine power within 1/2 of a mile. The Buick's throttle body made the same sound when I shook it but it works perfectly fine. I'll try swapping the pedals as well since it only seems to happen when I'm leaving from a red light or stop sign. I also ordered a Tech 2 which should make it much easier to diagnose this problem. Is it possible to disable the fan code with the Tech 2 or will I need to send my PCM to Lime Swap or PCM of NC?
 
OP
OP
UsernameIsTaken
I tried it with torque lite today, no dice. I did however notice that the absolute throttle position would stay at 28% minimum instead of 14% minimum when the pedal is released after pressing it a few times. This could indicate that one of the APP sensors is defective and is triggering the reduced engine power because one sensor is reading minimum throttle and the other is reading 1/3 throttle. If I no longer get reduced engine power after swapping it with the one in my Rainier, then I've found the cause of the problem. I did grab a pedal from an '02 Envoy the other day at LKQ but I didn't know that they changed the connector in '04 so I can't use it.
 
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Mooseman

Moderator
That will definitely confirm if the APP is defective.

I also ordered a Tech 2
Where did you order it from? If it's shipped within the US that's fine, but if from China, US CBP have been stepping up on trademark and copy infringements lately. One of our members' Tech 2 was seized by them with the possibility of fines. Luckily he was able to get a refund.

Is it possible to disable the fan code with the Tech 2 or will I need to send my PCM to Lime Swap or PCM of NC?
Tech 2 isn't able to do that so yes, you'll need to have it tuned.
 
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OP
OP
UsernameIsTaken
I ordered it from eBay. The seller was based in California if I remember correctly. I was going to order it from AliExpress but the shipping would've taken much longer and if US customs is indeed confiscating Tech 2 clones then I guess I dodged a bullet there. :2thumbsup:
 

TJBaker57

Well-Known Member
I did however notice that the absolute throttle position
The Tech 2 displays no parameter "absolute throttle position". (At least not for my 02 4.2l) It does display an "APP Average". Not sure of the significance this wording. There is also in the Tech 2 a "TP Indicated Angle". Just wondering what parameter your BlueDriver is reporting.
 

TJBaker57

Well-Known Member
Something I noticed between my 02 TrailBlazer 4.2l and my 05 Yukon 5.3. For the 02 4.2l my sensors read opposite each other, that is to say as one voltage goes up the other goes down. The sum is always the same as the reference voltage. For the 05 5.3l the readings are the same, they both go up or down together. Guessing maybe later year 4.2l systems may also run together and thus the changed connector to avoid a mismatch?
 
OP
OP
UsernameIsTaken
So far it appears to be the pedal that caused the problem. I swapped it for the one in my Rainier yesterday and drove about 4 miles with the A/C on and stopped at at least 10 red lights and stop signs to try to trigger the reduced engine power. No problems other than the fan code. I'd still have to test the Rainier to completely confirm that the pedal is defective but so far it looks that way. It does feel a bit sluggish though so I'll try pulling the PCM fuses to see if it improves.
 
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MRRSM

Lifetime VIP Supporter
Very Cool... The sluggishness should disappear after the Spark Plugs get to burn off anything residual left inside of the Cylinder Head. This is an artifact of the "Reduced Power Syndrome" as the PCM shunts Firing ALL (6) Spark Plugs down by 2-3 ...regardless of the cause of any triggered Reduced Power event. Treat your Fuel Tank to a "Double Scotch...(No Ice)" using some Chevron Techron and THAT should Pep the Motor up a bit. :>)
 

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