Car will lose power, strange codes

Tiny
CANNON1349
  • MECHANIC
  • 2008 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 137,000 MILES
The car will lose power after being driven for a little, saying "reduced engine power" and will hardly move, yet still runs. Someone ran the codes on it and got a P0641, however when I ran the codes I got a list like this:

- HO2 heater control circuit
- HO2 bank 1 sensor 2 heater circuit
- throttle body position sensor performance 1
- evap leak (large leak)

I did some research and some people say it's the computer.
Tuesday, December 31st, 2019 AT 8:37 AM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,940 POSTS
Hello,

It sounds like you have 3 problems here. first the bank 1 sensor 2 heater circuit oxygen sensor needs to be replaced, the throttle issue is because the PCM is going into limp mode due to a dirty throttle bore and finally the EVAP leak could be the supply line to the purge solenoid. here are three guides to help fix all three problems:

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

and

https://www.2carpros.com/articles/throttle-actuator-service

and

https://www.2carpros.com/articles/evap-system-code-repair

Please run down these guides and report back.

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Wednesday, January 1st, 2020 AT 11:59 AM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
Already replaced the oxygen sensor and still have the circuit codes.
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Wednesday, January 1st, 2020 AT 1:16 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,940 POSTS
Hmm,

The next step is to check the oxygen wiring. here is a guide and the wiring diagrams so you can see how the system works and which wires to test:

https://www.2carpros.com/articles/how-to-check-wiring

Have you serviced the throttle bore? Check out the diagrams (below). Please run this test and get back to us.
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Thursday, January 2nd, 2020 AT 7:27 PM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
I replaced the oxygen sensor and the throttle body position sensor. It ran good for a couple of weeks and now I have 7 codes for just the heater control circuit on bank 2, as well as another throttle position sensor performance 1, fuel pump relay control circuit, and p0641 5v reference circuit voltage. It seems like the computer may be the fault.
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Sunday, February 9th, 2020 AT 12:41 PM
Tiny
JOETECHPRO
  • MECHANIC
  • 705 POSTS
Hey CANNON1349,

Can you please update with a list of the actual fault codes you have stored?

Eg. P0641

It sounds like you have a fault in the 5V reference circuit so which would cause you to lose power to the accelerator position sensor. If you are having this fault intermittently you may have a short somewhere causing the 5V reference to drop out. The fault you are experiencing seems to be throttle control related.

I would not advise suspecting the PCM at this stage.

Regards, Joe
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Sunday, February 9th, 2020 AT 11:49 PM

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