The left driver's side Xenons on my W202 C43 AMG cuts out from time to time and the faulty bulb light in the cluster turns on. Turning the light off and back on usually solves this problem for a while.

Scanned the codes and came up with error B1400 which points to the ballast unit. I checked all the connections and plugs and all seems good, then removed the ballast unit from the vehicle. Managed to snap off one of the rusty holding bolts despite loads of WD40

Now that it is sitting on the workbench, is there any way I can test the module, or need to check for faulty parts? The price of a new unit is worth getting a heart attack Finding a decent second hand unit is difficult and could be dodgy to find one in good working condition.

Thanks for any advice

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What is the exact description of the trouble code? This is vital in solving the problem. As bulbs age, running voltage increases so if I was pushed into a guess, I'd say the running voltage is at the top of the ballasts limit.

I'd put the ballast back in and swap bulbs to see if the problem follows.

WD-40 is a miserable lubricant / penetrant, there are better ones out there.

I know I replaced a lot of ballast in building lights.Maybe automotive burn out too.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Thanks for the replies. The error code description didn't give more details and no voltage indication despite the lights being on during the scan.

The only other details noted with the error code was the following:
Software version: 14/97
Hardware version 211
Diagnosis detection 1/00

Light bulbs were changed in September 2014. Bulbs installed are currently Osram Xenarc Cool Blue Intense DR2 P32D-3. Great bulbs and light by the way.

I'll try switching bulbs left to right and check from there if the problem continues.