So I noticed the other day that both of my fog lights weren't working on my car anymore and figured it was just a blown fuse. I located the fuse box in the engine compartment per the manual and found the 15 amp fuse and replaced it. Still not working?
Does anyone know what else to check since I tried multiple new and used fuses in the slot and they're still not working? Up until a week ago they were both working so what could have happened?
Thanks,
Deus
There isn't much testing that you can do if you aren't handy with circuit troubleshooting between switches and modules which communicate with each other using voltage signals and over the CAN bus.
In your case you can use a test light and check for Power on both test tabs of Fuse 58. If there's power there you can turn ON the Fog Lamps and check for Power at their bulb sockets.
Anything beyond that and you'll want to use a scanner which can read live data from the BCM to see if it's receiving the voltage signal from the Fog Lamp switch (combination switch) and if so, if it's sending the request to the IPDM (underhood fuse box) to energize the integrated fog lamp relay over the CAN bus.
Here's the System Diagram and System Description:
One thing to notice in the Front Fog Lamp Operation part is that the Fog Lamp Relay is integrated (soldered) onto the IPDM printed circuit board. It isn't serviceable.
The way it's wired (starting from the bottom left), is when you turn ON the Fog Lamp Switch continuity is created between Combination Switch pins 2 & 13.
Moving up, the BCM sees the circuit completed between its pins 87 & 146. That tells it that the Fog Lamp switch is turned "ON" and it sends a request over the CAN bus (data lines) to the IPDM to energize the Front Fog Lamp Relay. The relay is energized and the circuit is completed between Fuse 58 (15 amp) and the Power side of the Fog Lamp bulb sockets and the fog lamps light up.
So this is why a good scanner comes in handy for this stuff. You can see if the BCM is getting the voltage signal from the Combination switch when you switch ON the Fog Lamps.
You can see if the BCM is sending the request to the IPDM to energize the Fog Lamp Relay.
And using the bidirectional control of the scanner you can command the Fog Lamp Relay to energize and take the Combination Switch out of the equation. It's so much faster and easier than using a multimeter and a test light
Thank you, very good information and explained in a way that will set me on the right path.
Up until a week ago they were both working so what could have happened?
Something broke.
Roger that. I just watched another video where this guy had a 2015 GMC truck and his fuse popped and his fog lamps stopped working. He replaced the fuse and they still weren't working. he had to use his OBD scanner to reset the BCM for the fog lights to work again.
I'm betting that might be my problem.