Chevy Colorado & GMC Canyon banner

4-way flashers on all the time

14K views 12 replies 5 participants last post by  Jose Concolino 
#1 ·
Hello.

I have my 2005 apart to do rockers. I had the battery disconnected for several days while I was welding and finishing. I put it all back together and hooked the battery back up and noticed the 4-wat flashers are on right as I hook up the battery. Anyone have any idea what is going on?

Thanks.
 
#2 ·
:welcome to C'Fans

Please clarify a couple of things so we don't start assuming. Was the battery disconnected prior to any welding action? Are there any aftermarket electronics installed on the truck, such as head unit/amp, remote start, security system? Does the Hazard switch control the lights i.e. can you turn the lights off? If not, disconnect the connector from the Hazard switch and see if that has any effect. The Hazard lights are controlled by the BCM after the switch provides a ground for the circuit. The Hazard switch could be failed closed or the circuit could be grounded prior to the switch.

Do you have a multimeter?
 
#3 ·
Was GM controlling many of the functions via the BCM all the way back in 2005?

I feel so old. It was so much easier when a switch actually just controlled the item being switched.

A multimeter is a critical item to any automotive toolkit. Knowing how to use it, and how not to kill yourself while using it, is equally important. Likelihood of death on a 12 volt system like our trucks is minimal, but 120 VAC and higher house wiring can be dangerous.

You can get a cheap multimeter at Harbor Freight that will cover 99% of anything you would ever do on our trucks, any year model. With a coupon and a separate purchase, Harbor Freight often gives them away free.
 
#4 ·
"Was GM controlling many of the functions via the BCM all the way back in 2005?"

Yeah, I think that literally all of the lighting circuits are connected to the BCM.

Old? I just breezed by 76! Remember fender skirts, curb feelers and 4 wheel drum brakes, tires with tubes, chrome acorn nuts on the head bolts?
 
#8 ·
Well, that is strange. The White wire in the connector is the signal wire directly from the BCM and the Black wire connects the circuit to ground. The Gray is for dimming. Removing the connector should have removed any ground source.

Power for the turn/hazard bulbs comes from two sources, fuse 28 (TURN/HAZ RR) and fuse 37 (TURN/HAZ FR). Both sources feed directly to the BCM. The BCM decides whether to flash the lights for turn or Hazard.

The symptoms point to either a wiring issue or the BCM. The BCM may be stuck in Hazard mode. Try disconnecting the battery negative cable and touching it to the positive terminal of the battery. These trucks seem to have a lot of weird electrical problems develop when the battery is disconnected.
 
#9 ·
If you have had the battery disconnected then you probably confused the BCM on power up. This happens frequently when the second battery cable is reconnected. If the power bounces up and down a couple of times while the BCM is rebooting, many times it does not come up correctly. Disconnect one of the battery cables and touch it to the remaining one for a few ( like 10) seconds. Then wait a few minutes and reconnect the cable. When reconnecting the cable put it in place and do not move it while tightening it down. You are trying to prevent a power off an on bounce while reinstalling the cable.

Doing this should cause a full BCM reset.

Note: You do not necessarily have to disconnect the cables at the battery to do the reset.
 
#11 ·
OK. Got my truck back together. Tried to do the BCM reset with no luck. Pulled the switch out and tested it with my meter and it seems to test good. Tried disconnecting the switch, they are still on. It is weird I did not have any problems before I disconnected the battery.
 
#12 ·
Although the battery was disconnected, there is a small chance that the welding somehow affected the BCM. It is also common, with these trucks, for weird electrical problems to show up after battery disconnect.

Hard to troubleshoot from a distance. Maybe try disconnecting the connectors at the BCM and checking the condition of the terminals. The BCM is located behind the right kick panel. The Service Manual cautions to always remove the black connector first, then the gray connector. When reinstalling, always connect the black connector first. The Manual doesn't explain why. The wire from the HAZARD switch is in the gray connector.

The battery itself can cause strange reactions from the computers. How old is it? Maybe have it load tested.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top