No Headlights

Thanks for this thread, and big thanks @Jimmyh for the schematics. I had the same problem recently (headlights don't turn on, but flash works). Here are some steps I took that I'm sharing in case they help others.

I started by testing the bulbs. Jumpered pins 3 and 5 on the head relay (from Jimmyh's schematic) with a spare piece of 14awg. I ended up testing out the connection to the bulb connector as well, with a DVOM. Connectors tested fine and bulb low filament didn't work. Had blown on both bulbs. Replaced them.

Next, I engaged the headlight relay by connecting pin 14 on the Body ECU connector (B5) to ground using a longer piece of 14awg. I used the same ground that the BCM does, which is located just under the fuse box to the left behind the driver's-side kick plate, which isn't too bad to get off. Shouldn't matter though, any ground will do. Pin 14 is located here:

Anything like 14 or 16awg should shim down into the back of the connector and contact the pin easily enough. You can find B5 plugged into the body ECU on the back of the fuse box. That let me know my relay and the circuit out the lights was good, and with good bulbs, activated them.

Next I tested the combination switch on the steering column stalk looking for continuity between pin 17 on connector B5 and ground, same ground as above. With the switch in the headlight position, you'll have continuity. With it in off, you won't.

That tested out good, so basically the body ECU in the middle seems like the problem.

I have temporarily rigged up a fix by jumping the two pins I mentioned (14 and 17) on the back of the body connector:


This lets the switch directly activate the headlight relay while I wait for my ebay body ECU to arrive. Couldn't find much information about what to look for when swapping ECUs, so went with a salvage that was as close as I could find to mine. Anyone have more information about what details matter when swapping these? They're programmed, so if the model they're programmed for is close to yours - it should work out? No idea, any feedback helpful. Thx.

 

Good job tshooting.

Body ECUs should work as long as it is basically the same.

 

^

 

New body ECU did the trick! Am hoping to have the time to diagnose the old board to see if I can't fix it up for a spare but you know how it goes... Stuff starts working and the motivation drops off pretty quick. We will see, will report back if I come up with anything interesting that can help others

 

Sorry for bumping an old thread but the issue I’m having is that the high beams work & the low do not. I checked the fuses & the relay but still nothing. I’m trying to find more info via TW I came across this thread. I’m not great with electrical so I wanted to ask if the body ecu replacement is a fairly involved process.

FYI - the truck is a 2009 base model.

 

Have you checked/replaced the bulbs?

 

Yep. That was the first thing I tried.

 

Do you have a test light?