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Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Chevy
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Experience:  16 years of experience
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Second opinion] - 2002 Chevy Impala LS 3.8 L - I have this

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Second opinion] - 2002 Chevy Impala LS 3.8 L - I have this issue.....back up/reverse lamps come on when foot is on brake and shifted into "R" but the reverse lamps go out as soon as foot is removed from brake pedal to start backing up ( I can hear the backup lamp relay in fuse box click off when brake pedal released) - I tried a new relay but had the same issue. Brake/parking/head lights work fine.....problem is ONLY when removing foot from brake pedal to move backwards...if I keep my foot on brake pedal and shifter in "R" the back up lights will stay on.

Welcome, I'm Chris (aka Moose), my normal schedule online is around lunch and after dinner till early morning.

Was this a prior police or emergency vehicle?

Customer: replied 8 months ago.
No police/emergency package - standard 3.8 L Impala LS (2002) with 63,000 miles. All other lights, signals, etc working fine. I had replaced bad hazard light switch because the turn signals were not working right (fixed turn signal issue) but the back up light problem was happening before I replaced hazard switch and has continued after. When I apply brake to shift into gear ("R") I hear the relay click and backup lamps come on.....but as soon as I take foot off brake (shifter still in "R") and go to back up the relay clicks and the backup lamps go off.....tail lights, headlights, signals, etc all still work normally.I also just bought an OBDii scanner and have checked veh - no codes generated.
Customer: replied 8 months ago.
I also removed rear trim plate to access bulb housing/wires - all appeared ok (no nicks, corrosion, etc) and replaced the back up bulbs with new ones - problem still occurs......and if I shift back into Park then put into "R" again (with foot on brake) the reverse light come on but go off when foot is again released from brake pedal to back up,

Here is the wire diagram.

This is going to be a BCM or PCM module issue. They control the back up lamp relay. Do you have access to a diagnostic tool that can monitor the inputs and outputs on these modules?

What now

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Thanks for using Just Answer, and rating me so I am compensated, Chris

Customer: replied 8 months ago.
Can the OBDii scan tool be used to monitor these inputs/outputs? ( the scanner I have allows for "live data" results - I had checked that too but there was nothing reported as being wrong - I even shifted in reverse and produced the problem while the scanner was hooked up and reporting live data but nothing showed up).Any chance it could be a bad ground issue?

We need to monitor the transmission range sensor reading the PCM is getting while in reverse to see if that signal is changed when braking and not braking. The only ground I can see possibly related is on a transmission to engine mounting bolt/stud next to the starter.

Customer: replied 8 months ago.
Ok - what kind of instrument do I use to check that signal? The PCM is in the air cleaner box correct....and do I monitor the black/white wire or yellow wire coming from PCM? (looks to m it would be the black/white wire).

A tech 2 diagnostic tool is needed to monitor this signal. It is not a wire test since it is a data communication wire.

Customer: replied 8 months ago.
Ok - I understand that is a really a dealer only option.......I will check the ground you mentioned to see if that helps.Would cleaning the contacts on the PCM or BCM plug connector ends/ports help at all?? I have some DeOxit electronic circuit cleaner. The fact that there is absolutely no other issue with the vehicle except for the back up lights going out problem had me thinking the PCM and BCM were ok (as I've heard a bad BCM causes multiple lighting, instrument, etc. errors).

Cleaning connectors will not hurt.

A module has many responsibilities. You can lose just part of it and the rest will remain working.

Hello again Chris here,

  1. I have to assume you were not pleased with my help, because you have not replied or rated the post.
  2. What would you like to do regarding your question now?
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  4. This post is coming up on the 7 day mark where it times out. That can prevent me from being able to post answers to your replies.

Thanks Chris

Customer: replied 7 months ago.
Your info was informative but other than it resulting in my apparently having to take it to a dealer and spend a fortune to have them diagnose and find problem using a specialized tool it didn't really help me or provide a solution.Thanks anyway, I will rate you as good based on the advice given


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