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Strange engine codes randomly appear

Tiny
I_MBOWTIE
  • MEMBER
  • 2008 CHEVROLET EXPRESS
  • 6.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 167,000 MILES
B2991 Right front door ajar circuit malfunction, C0050 Right rear wheel speed sensor circuit malfunction, P0121 Throttle/pedal position sensor/switch "A" circuit range/performance. Plus the ABS and The stabilitrac service light comes on randomly too, even just sitting idling. I changed the pedal position sensor and the right rear wheel speed sensor and erase the codes but in a few days they come back, it does seem to be more prominent in wet weather, do you suspect the PCM? I inspected wiring and connections and all looks good.
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Wednesday, November 7th, 2018 AT 12:25 PM

11 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Did all of these codes come up at once? Can you clear the codes and then turn the key on and without starting the gnien see what codes come back? This sounds like two problems. I would service the throttle bore first for the P0121. I do not think PCM because the door and ABS does not go through it. BCM maybe. Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Friday, November 9th, 2018 AT 12:08 PM
Tiny
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Yes they all come up at once, but do not come back just turning the ignition on. I have to actually run the engine and then not all of them come back all together every time, they are pretty random. Could go for days before they pop up. But it is always those same codes randomly with the P0121 being the most frequent, but we have been getting the ABS/Stabilitrac service light a lot lately. That is when I tried replacing the right rear wheel speed sensor.
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Friday, November 9th, 2018 AT 4:29 PM
Tiny
KEN L
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Okay please service the throttle body. It sounds like one problem or three like a bad ground in the engine or passenger compartment let's start by checking the grounds by following this guide and the BCM wiring diagrams below.

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

Check resistance to ground on both the BCM and ABS module. Let me know what you find.
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Saturday, November 10th, 2018 AT 10:02 AM
Tiny
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  • 40 POSTS
Thank you for the diagrams they will be very useful. But there are some abbreviations that I am not familiar with, What is "LOF REF" and how do I test these? And it does not show where all the grounds are so I can check them as well.
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Sunday, November 11th, 2018 AT 8:21 AM
Tiny
KEN L
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The grounds are listed black/white on the first diagram and just black on the ABS module. Do not worry about the LOF REF which is a monitoring line.
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Monday, November 12th, 2018 AT 9:54 AM
Tiny
I_MBOWTIE
  • MEMBER
  • 40 POSTS
I removed and thoroughly cleaned the throttle body and performed a manual throttle body relearn procedure, then drove the van for twenty five to thirty miles and did another relearn but I am still having high idling issues, will this eventually smooth out on its own? Also, I forgot to mention this was a Texas vehicle so the under-body is amazingly clean and all grounds and wiring look great. I am still getting the P0050. I removed and inspected the ABS module but cannot see anything obvious, do you think it is a bad module?
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Sunday, November 18th, 2018 AT 3:07 PM
Tiny
KEN L
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Is it a p0050 or c0050?
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Monday, November 19th, 2018 AT 11:45 AM
Tiny
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Oh, I am sorry, my mistake C0050. I clear this code and it comes back immediately.
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Monday, November 19th, 2018 AT 3:23 PM
Tiny
KEN L
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Lets check the connection between the ABS module and the sensor use the wiring diagrams for the ABS above and the guide. Here is the location of the module below.
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Tuesday, November 20th, 2018 AT 9:44 AM
Tiny
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Update, on the C0050 after a thorough inspection I found a nick in the right rear speed sensor wire leading to the EBCM about two inches "inside" the wire loom, must have been there since production since it was found inside the loom, after repairing it the code no longer returned. Thank you for all your time and references.
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Saturday, December 1st, 2018 AT 11:28 AM
Tiny
KEN L
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Wow good find on that. Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help

Cheers, Ken
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Saturday, December 1st, 2018 AT 11:38 AM

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