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2005 Cheverolet Avalanche Headlight Mystery

Tiny
GCROSBY
  • MEMBER
  • 2005 CHEVROLET AVALANCHE
  • V8
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
I have the exact same issue as Randoger who posted "2005 Chevy Avalanche gremlin high beams" in January 2008. My high beams on my 2005 Avalanche come on when turning the ignition off. Day time or night. Sometimes they go off by themselves but will come on by themselves after several hours. No tail lights. No perimiter lights no low beam lights. Just the high beams. For now I have taken the fuses out that control them. No problems since then of course. Any ideas for the cause or method to track it down. Was this issue ever resolved for Randoger.I know the issue is 3 years old but am hopeful that a solution was found.

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Tuesday, January 11th, 2011 AT 2:28 PM

9 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Get a scan done to see if any trouble codes are present system. Scan tool must be able to retrieve B codes, meaning code for Body Control Modules. If any trouble codes are present, it would help in the diagnostics of the problem.

Attached are the schematic for the headlights.

When problem occurs, unplug the high beam relay and test terminal 85 for continuity to ground. If continuity is found, the BCM is activating the relay.
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Tuesday, January 11th, 2011 AT 4:32 PM
Tiny
GCROSBY
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  • 6 POSTS
Excellent tip to verify the circuit.I will try to get the codes checked. You mention "B" codes. When I asked the local AutoZone (which does code scanning for free) he was completely unaware of body codes and didn't think they could read those.I will need to make an appointment someplace to get any "B" codes that may be registered. Do the codes get "saved" or does the problem have to exist at that time you try to read the "B" codes?
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Tuesday, January 11th, 2011 AT 6:19 PM
Tiny
KHLOW2008
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  • 41,815 POSTS
Codes would be stored in the BCM unless the battery has been disconnected or there is a fault in the wiring circuit.

There are B, C, and U codes which normal code readers would not be able to read, except for P codes. Only scan tools with multifinctions can read such codes and Autozone code readers would not be able to retrieve them.
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Tuesday, January 11th, 2011 AT 7:02 PM
Tiny
GCROSBY
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  • 6 POSTS
I have been unable to get the "B" codes checked yet but have additional information that may help. When attempting to check the circuit point 85 of the High Beam Relay I put the fuses back in. The high beams were off.I pulled on the "Flash To Pass" (turn signal) lever and both High and Low Beams came on as designed. When I released the lever the high beams stayed on.I tested point 85 and it had continuity to ground.I replaced the Relay with an identicl relay and the high beam lights still stayed on.I have now pulled the relay leaving the 2 fuses to prevent draining the battery. Does the use of the "flash to pass" to recreate the problem provide you enough information to diagnose the root cause or do I still need to get the codes read. Thanks for your help!
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Tuesday, January 18th, 2011 AT 12:22 AM
Tiny
KHLOW2008
  • MECHANIC
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That seems to indicate a faulty switch that is intermittently self activating. When light turns on, unplug the switch wire and if light goes off, the light switch is faulty.
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Tuesday, January 18th, 2011 AT 12:23 PM
Tiny
GCROSBY
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I was finally able to reproduce the issue. It has taken a couple weeks to occur again. In the house garage went out and the high beams were on (only). Disconnected the multi-pin connector to the switch (on the dash with the auto vs. Manual head light switch). No change. The high beams stayed on without the switch being plugged in. Any thoughts. And no :-( I still don't have the body codes to help yet.
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Tuesday, February 1st, 2011 AT 8:31 PM
Tiny
KHLOW2008
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Since high beam relay and lighting switch has been tested to be good, the only other component that can keep the lights on would be the Body Control module.
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Tuesday, February 1st, 2011 AT 9:19 PM
Tiny
GCROSBY
  • MEMBER
  • 6 POSTS
Since the flash to pass still lights the low beam headlights but not the high beam (since the relay has been removed). Is there a quick way to test the flash to pass switch? I agree everything else has been tested but I would hate to buy a new BCM and have it occur again. Thanks for the quick response! Is there a connector that is easy to disconnect the pass to flash by unpluging?
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Tuesday, February 1st, 2011 AT 9:31 PM
Tiny
KHLOW2008
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From the schematic you can see that the flash to pass switch has a Yellow/Black wire that if grunded would keep the high beams on. If you disconnect the switch and light still stays on, the switch is not the problem.
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Tuesday, February 1st, 2011 AT 9:50 PM

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