These two lights came on at the same time the other day, they turn off whenever I shut the engine down but come back on while driving. As far as I know the brakes were done recently and I saw them ~2 months ago when the truck was safetied and they were fine. Anybody know what causes this and what needs to be fixed? Thanks.

 

Have you checked the ABS/speed sensor on the rear differential? It could be bad or could have metal fragments on it causing the sensor not to be able to send out the correct signal. It is on top of the differential housing, on the pinion side. It should have a 2 wire plug in. It is held in there with a 13mm head bolt. Remove the bolt, blow the dirt and debris away from the sensor, turn the sensor side to side, and pull it straight up. Then see if it has any garbage on it and go from there.

 

Might wan't to check the wiring to it if cleaning the sensor dosn't help, I've seen more than 1 ford where the wires were all green and coroded inside the insulation

 

Sounds like a plan, thanks

This makes sense because when I'm driving the light comes on after I'm stopped (at a stop light for example) then accelerate. Might be crap on the diff sensor.

 

Low brake fluid will cause both of those, as well.

 

Did you get it figured out? I had those lights come on in our Aerostar van after doing about 2 miles worth of cookies in an icy parking lot. Never could figure out how to get them to shut off. Even after the van sat for a couple months and got a new battery they still come on occasionally. I'll have to check to see if that sensor is in the same spot and see if its all mucked up. Its always had plenty of fluid in it. I've had the fluid get pretty low in on of my trucks and I don't recall either light let alone both coming on from low fluid but maybe there was something else wrong there too.

 

If the fuse for your brake lights goes out it will activate the ABS light as well.