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Brake system warning light issue

Tiny
FGR8FRK
  • MEMBER
  • 2007 CHEVROLET IMPALA
  • 3.9L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 232,000 MILES
Car has been sitting for a few months, pulled into garage to fix a few items to try and sell. Took for a test drive and Red Brake, Anti-Lock, And ABS lights turned on.
The brake light will sometimes go out then come back on but the other two flash randomly together with no certain pattern like a loose wire. Hooked a Creader scanner to it and it says not able to connect to ECU and check reader connection. It does read other items like engine coolant, RPMs, throttle position etc. Just seems to not read that one area.
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Friday, February 18th, 2022 AT 12:43 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi,

By chance, have you checked the brake fluid level? Don't laugh, but that can cause the lights you are referring to.

Also, are you able to connect the PCM with the scanner or is there no power to it? Does pin 16 have power to it at the DLC?

Let me know.

Joe
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Saturday, February 19th, 2022 AT 2:23 PM
Tiny
FGR8FRK
  • MEMBER
  • 46 POSTS
Brake fluid was slightly low just below the max line. Pin 16 had 12.4 volts.
Scanner reads other parameters, just not the area that deals with the BCM.
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Sunday, February 20th, 2022 AT 11:32 AM
Tiny
FGR8FRK
  • MEMBER
  • 46 POSTS
I have found the issue. This is my daughter's car, and she recently had the transmission replaced with a used one. While surfing the web for the U0121 code I found an article which talked about the plug on the transmission being loose or not fully seated, found the plug, removed and plugged back in, code gone dash lights out. While driving and hitting a hole lights came back on, stopped and wiggled plug and lights go out. So now I'll pull and clean but is there something else you could suggest while I'm in there?
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Sunday, February 20th, 2022 AT 2:43 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi,

The code certainly helps. I'm glad to know you found the issue. However, is it the connector that is bad or a clipping issue? You don't want it to fall out every time you hit a bump.

Let me know so I can try to help.

Take care,

Joe
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Sunday, February 20th, 2022 AT 7:26 PM
Tiny
FGR8FRK
  • MEMBER
  • 46 POSTS
The plug does lock, removed and sprayed down with contact cleaner. Plugged it back in but if it gets bumped it sets the codes.
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Monday, February 21st, 2022 AT 11:11 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Inspect the pins inside the connector to make sure nothing is pushed back in causing a weak connection.

They never make things easy.

Let me know.

Joe
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Monday, February 21st, 2022 AT 7:34 PM
Tiny
FGR8FRK
  • MEMBER
  • 46 POSTS
Unfortunately, I think it has a broken wire.
With a snake camera trained on the dash and watching on my phone I grasp the wires by the plug so they wouldn't move and moved the wires around back roughly 3 inches from the plug back to where there was a bend, if I moved it a certain way the lights would go out, finally narrowing it down to a fine movement to make them go out and come back on.
The question here is, is there 1 particular wire to concentrate on or do I have to go to a junkyard and snip a plug and splice all 17 wires? :(
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Tuesday, February 22nd, 2022 AT 12:20 PM
Tiny
FGR8FRK
  • MEMBER
  • 46 POSTS
Update: Problem definitely found.
I went back out and was preparing to try and separate each wire to see if I could get lucky and find the culprit wire.
As I was moving the harness around to get a clear path, I noticed a ground wire coming out of the loom that was down beside the transmission and wasn't connected.
I set up my camera again and low and behold, when I touched it to metal the lights went out, found where it looked like it was supposed to mount and so far, so good. So next I'm going to go over their work and see what else wasn't reconnected.

Thank you for your assistance!
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Tuesday, February 22nd, 2022 AT 3:05 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi,

You are welcome and thank you for the update. I'm glad to hear you found it. Electrical issues can be a nightmare. LOL

Regardless, please feel free to come back anytime in the future if you have questions or if we can help. You are always welcome here.

Take care,

Joe
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Tuesday, February 22nd, 2022 AT 6:56 PM

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