Hi everyone. 2003 Saturn L300 sedan

Anytime my battery is connected, my brake lights are blinking. It’s not set the same timer as the hazards or turn signals. It’s also not the full strength, honestly something I could miss if I didn’t know what I was looking for but multiple people have noticed now.

Also, my headlights flash when they are in the “auto” position and the car is off sometimes. It’s random when it happens.

Also, the process of connecting and unconnecting my battery causes my trunk to lock and unlock?

 

What do you get with the battery hooked up like normal and key off?

 

the blinking lights

 

Scan all modules.

 

how do i do that

 

How long has this been happening? Has the turn signal/headlight switch been replaced recently?

 

the blinking has happened for weeks. the switch has not been replaced how much does that usually run

 

Food for thought

Could this possibly be the ambient light sensor that controls the DRLs? Then the brake lights wouldn't be flashing, they would be the running lights turning on and off and on and off along with the high beams of the headlights. The timing would be related to how that light sensor signal is processed. It's probably going rail to rail sending an oscillating signal to the BCM and the result is on off on off on off in a very regular timed pattern

 

I am away from home and my manuals, however all the lighting except turn signals are BCM controlled. 03+ cars are slightly different from the 00-02 cars. They use the low beams for d.r.l. Very possibly the ambient light sensor/BCM failure on this car. There was a very experienced 03 owner on Saturnfans but I have not seen him here yet.

 

I'm not a mechanic, but if it was my car, I'd clean the cables and posts on the battery and start looking for a loose ground connection. BUT, like I said, I'm NOT a mechanic.