A140 BAS/ESP Light

[Rob140]

New to the Forum but my wifes A140 Automatic has limped home with the BAS/ESP light on. Local Mercedes Specialist said it was the brake sensor, changed it and all appeared well for 500m before light returned. Main dealer said it could be many things. Can anyone give guidance to what I can check myself befoer expensive trip to dealership?

 

[television]

New to the Forum but my wifes A140 Automatic has limped home with the BAS/ESP light on. Local Mercedes Specialist said it was the brake sensor, changed it and all appeared well for 500m before light returned. Main dealer said it could be many things. Can anyone give guidance to what I can check myself befoer expensive trip to dealership?

I have known 2 cars where the brake light switch has failed in a very short time, they are only £9 and it must be worth trying again

 

[K-T]

That's what I was told for my SLK, four switches later it's now in to have its ESP computer changed for £1000. Symptoms were exactly as described, you could also fix the problem just by disconnecting and reconnecting the installed switch, took just a few minutes. Eventually it couldn't be fixed this way anymore and just stuck failed with no brake lights, great design Merc - NOT:roll:

To diagnose this problem you need two things, one of which is a new switch. Use a multimeter to discern how the switch works and the points on the actuator rod which cause the various contacts to close. Compare this to the installed switch, if they match then be suspicious. I plugged the car into STAR with the switch terminals connected to multimeters. With STAR set to monitor the switch positions you can see how the ESP computer interprets the switch terminal outputs, in my case they disagreed, ie I could watch the switch contact being made on the multimeter but STAR showed it remaining open. You can also do "actuations" on STAR, tell it to put its brake lights on via the ESP module, if it doesn't then you have more proof that the ESP module is cooked.

Hope this helps.