Greetings and best wishes to all for 2011,

I have a dash light for the ABS system that comes on about 80% of the time that I drive the car but it does not come on as soon as I start up, and most times it does not come on until I have been driving for quite a while. I have been able to determine thanks to the lousy NYC weather that the Anti lock brake system DOES work when the light is NOT on and DOES NOT work when the light IS on (as you would expect). This indicates to me that some electrical component is intermittently failing. Does anyone know which one it might be? In other words is there a component that has a history of this type of behavior. Troubleshooting a component that fails intermittently can be difficult and I am hoping for a leg up from the collective wisdom of this fine assembly.

Thanks,
Lenk

I would clean the ABS sensors on the front wheels first. You can do this with the car on the ground. Turn the wheels hard to one side, take an allen key and back out the bolt holding on the sensor, gently wiggle the sensor out of the hole, clean all the metal crud off the sensor, slide it back in, tighten the bolt, turn the steering wheel and do the other side.

If the 240 has wiring connectors under the hood where the wires for the sensors clip into the main harness, I'd clean those connections, too. I know the 940 has those, I would assume the 240 does, too.

You are not having problems with an intermittent speedometer, right? That + ABS fault suggests wiring for the sensor in the diff is suspect. the rear sensor does triple-duty, sending info to the ECU, the speedo, and the ABS computer.

john

If he lives in New York I probably wouldn't try to remove the sensors, just use some compressed air and blow of all the metal dust, make sure the ring has good indents and not too rusty. If that doesn't work and you have no speedo stop starts then buy 1 sensor and change the passenger side first.

Dear John and Paulli,

Thank you for your responses. You have answered my question so well that it even addressed the part I failed to state in my post. Yes! the speedometer has stopped working on two occasions. So if you would be kind enough to indulge a further question; which part should I change first, the differential sending unit or the wheel sensors starting with the passenger side?

This Brickboard (meaning posters like you guys) are such a pleasure to correspond with that I almost don't mind buying the parts. I'm going to price them out right now.

Double thanks to you both,

Len K.

Cleaning the front wheel sensors is a routine maintenance item. I clean mine once a year; they are always covered with crud. You should do this anyway. When the ABS engages, clean sensors will make a difference in how well the system performs.

Your immediate problem, however, is clearly the rear sensor. Or more likely, the WIRING to the sensor. Get the rear of the car jacked up and supported on jack stands at the rear jack points. Go under and visually inspect the wiring, you will likely find that there are a few places where it is compromised (typically where it bends or flexes). The wires from the sensor are attached to it with the usual removable connector. Clean things up and gently unclip the wiring, and follow it up into the car body. Figure out how much of the wiring needs to be replaced, cut new wires, and install the new stuff in place of the old re-using the gray plastic protective sleeve and the connector(s).

No need to remove or clean the rear sensor itself. Sealed inside the diff housing, it should not be dirty.

Wear safety glasses when you're messing about under the car, you'll knock a lot of nasty grit loose while you're playing with the wires, and it's very unpleasant to get any in the eye. Very.

John