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Ivan, ASE Certified Master Technician
Category: GM
Satisfied Customers: 4871
Experience:  ASE Master Tech.20+ years exp. 9 years self employed. Participant on AutoLab Radio broadcast
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GM chevy: have a 2004 chevy trailblazer with code P2135 P2138

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have a 2004 chevy trailblazer with code P2135 P2138 and P0641 already changed the app and also check 5v on the fan, ac pressure,TP sensor all 5.0 v also sent in pcm to have check it was good

Hello and good evening. Do you still get those 3 codes to reset after you clear them? Also, when you replaced the APP sensor, did you use a GM sensor or aftermarket?

Your JA Expert,


Customer: replied 4 years ago.

sorry it took me so long had problems with my computer but any way yes after i earse these codes all 3 come back. I replaced the app with an after market i was thinking the same thing so i returned the new 1 for warranty and replace it with another after market


Was it a Dorman unit?
Customer: replied 4 years ago.

dont understand Dorman unit part #SU9403

Ok, let me look up that part number and see who the manufacturer is.
Customer: replied 4 years ago.

its a duralast

Ok, I checked that out and it may be a quality aftermarket component. There are many that are made in China that are sublevel and have caused serious issues. The problems appear to be 5 volt supply lines that are showing higher than 5 volts on them. I would like you to start at the APP sensor and measure your voltage on the White/black wire and Tan wire. They should register 5 volts. Let me know what you show
Customer: replied 4 years ago.

did u want me to measure it with it on or just the harness

Measure it with in on, in place and with the engine running. If the voltage is higher than 5.6 volts, those codes will set. I would like to see first, what voltages are present, then with you still monitoring the voltage, clear the codes and let's see if the codes return. We will test further, but I'd like to start here.
Customer: replied 4 years ago.

k will let u no tomorrow

Great, sounds good. Have a great night.
Customer: replied 4 years ago.

hey i check for volt white/blk an tan wire and was reading 0.320 what i did is i had a couple of needles into the back of the app connector will that work? Also i got another code fan speed sensor P0526

Back probing is ok, what I want to make sure of with your test is that the black lead of your meter was to ground and the red lead when to that white/blk wire and then red to the tan wire. Both of those wires are 5 volt reference wires. They should have measured 5 volts each. If you went across the 2 wires, then that would be the voltage difference between the two, and they should have been almost exactly the same. Let me know.
Customer: replied 4 years ago.

k will let u know

Great, talk with you soon.
Customer: replied 4 years ago.

ok the white/blk wire reads 5.03v and when i clear the code there is no change and the tan wire reads only 4.75 and when i clear the code it reads about 4.83

Do all 3 codes come right back?
Customer: replied 4 years ago.

yes they do right away

Customer: replied 4 years ago.

I allso check voltage at the TP sensor and the gray wire had 5.0v with no change when reset code and the lite blue/bk wire had 4.73v it would change to 4.83v when reseting code

Ok, I'll get back with you in a little while, I'm out to dinner. Let me get my info system in front of me and I'll give you some tests.
Ivan and other GM Specialists are ready to help you
Customer: replied 4 years ago.


I just got back to the computer. I'll send some tests to you very soon.
Customer: replied 4 years ago.

k i check map, cooling fan, A/C pressure all reading between 4.69 to 5.0v didnt ck the fuel tank sensor also ck #54,55,62,63 at the pcm C1 and #49,60 at the pcm C3 all reading between 4.70 to 5.0v let me know what else i can check thanks

Ok, I'm going to look at some info and get back to you shortly. So far this deviation from 5 volts does not seem to be reality. I will get back to you shortly.
I am suspecting a faulty PCM, but first, look closely at the wires going to the throttle control motor. Those wires tend to become damaged and if they are grounding to each other or to ground, it could take the 5 volt reference with it. If they look ok, I am suspecting the PCM is internally faulty. Let me know what you see.
Customer: replied 4 years ago.

yes i have ck the wires going to the throttle control and they all look good thats y i sent the pcm to have ck that was my 1st thought but according to that nationwide parts in FL it was k

Then I would like you to try my original suspicion. Pick up a factory APP sensor and let's see what happens when you install that component. I have seen horrors with aftermarket APP sensors. Let's not bypass exploring it as an option.