another headlights go off when driving thread

[mark'stb]

Maybe once or twice a week the low beams go off when driving. May stay off for 3-5 minutes, may stay off until next restart. I replaced the hdm and they worked fine for a month or so and replaced the hdm again. Question is: is it the underhood fuse block or bcm causing this?

 

[16vcabman]

What is hdm?

You need to determine with a volt meter where the system lost the power. Just throwing parts at it is not a solution and can get expensive.

 

[Blckshdw]

What is hdm?

It's the headlight relay in the front fuse block. That tends to be the culprit in other situations like this one.

More troubleshooting needs to be done. If the problem is intermittent, and inconsistent, there could be a break somewhere, either one of the traces on the underside of the fuse block, or in wiring somewhere. Hopefully the next time it happens, you'll be close to home, so you can check different points and hopefully narrow down your search area.

 

[mark'stb]

The problem recently is by the time I get home the headlights are on. I wiggled whatever wiring I could under the hood and the lights never went out. Not related but, I've seen numerous problems with this style fuse blocks in Corvettes,and not many bcm issues. I figure since they are of similar design, the fuse block may be my first choice as the cause,

 

[budwich]

A flash light and meter should be your "vehicle tool box" for the next little while so that when the occasion calls for it, you are ready. Since you have have had multiple hdm replacements, have you actually ever did an "autopsy" on a failed unit to see what's up... of course, you can always compare your "investigation results" by checking against a working unit. Depending on the depth and measurements, you might have your answer. Further though, it depends on what kind of module you are using for a replacement as most would say here that OEM is needed (even a used one) as the "power switching FET" in the module is usually the "weak link".

 

[TJBaker57]

What is hdm?

"Headlight Driver Module"

 

[Mooseman]

What brand HDM did you use? Other than ACDelco tend to fail prematurely.

 

[gmcman]

Check the headlight pigtail sockets for any signs of corrosion or slightly burned plastic. There's a chance you could have some excessive resistance overloading the circuit.

 

[mark'stb]

A flash light and meter should be your "vehicle tool box" for the next little while so that when the occasion calls for it, you are ready. Since you have have had multiple hdm replacements, have you actually ever did an "autopsy" on a failed unit to see what's up... of course, you can always compare your "investigation results" by checking against a working unit. Depending on the depth and measurements, you might have your answer. Further though, it depends on what kind of module you are using for a replacement as most would say here that OEM is needed (even a used one) as the "power switching FET" in the module is usually the "weak link".

They all have been GM hdm's. Can't diagnose the problem unless it is occurring and I can not duplicate it in the garage. I have learned to drive with the foglights on so when they do go out, I am not totally in the dark until I turn on the high beams.

Check the headlight pigtail sockets for any signs of corrosion or slightly burned plastic. There's a chance you could have some excessive resistance overloading the circuit.

Done that, all looks good- not saying internally the fuse block does not have an intermittant open. Even reached into the terminals with a pick to put more tension on the therminals.