Engine Control Unit

[Geoff1949]

Hi, I’ve just joined the Forum as am in need of some advice. I have an old Mercedes A Class and the headlights intermittently flash on and off even though the lights are not on. My garage have told me that the ECU is defective and that is causing the problem. A new ECU would cost around £1400 so I’ve been looking at second hand units. The trouble is that I can’t find the exact same part number. My unit Merc No is A640 150 47 79 Bosch No 0281 012 430. I have found an ECU on eBay but the last 4 digits are not the same, i.e. Merc No A640 150 49 79 Bosch No 0281 012 432. The question is how important are the last four digits and basically would this part fit my car. Any advice would be much appreciated.

 

[LostKiwi]

Hi and welcome.

You don't say where you are but I think it's time to find another garage.
As far as I'm aware the lights have nothing to do with the engine ECU.

 

[Geoff1949]

Hi and welcome.

You don't say where you are but I think it's time to find another garage.
As far as I'm aware the lights have nothing to do with the engine ECU.

 

[Geoff1949]

Hi, LostKiwI, many thanks for the speedy reply. I don’t know much about it but I think in view of your comments, I will take the car in to another garage for diagnosis Have you ever come across headlights flashing on and off while driving (without the lights on) and what might be the issue?

 

[LostKiwi]

No never encountered it.
As to what it is it could be a bad headlight switch, front SAM, poor connection.
What part of the country are you. We can probably recommend a good indy (independent Mercedes specialist) or if you're lucky @GLK our resident expert on your car will be along shortly with some ideas.

 

[Geoff1949]

No never encountered it.
As to what it is it could be a bad headlight switch, front SAM, poor connection.
What part of the country are you. We can probably recommend a good indy (independent Mercedes specialist) or if you're lucky @GLK our resident expert on your car will be along shortly with some ideas.

Hi, again, LostKiwi, thanks for your advise. I live in Leatherhead in Surrey and would be pleased to know if there are any recommended garages near me you think might be able to help.

 

[ZZZZ]

Hi Geoff,

I'd start by checking wiring in engine bay, and headlights' plugs / sockets.

If the lights flash in sync, then it might be a problem with SAM (Signal Acquisition and Actuation Module) - there are a few relays and it is worth checking those. SAM is located behind the carpet to the front of passenger's footwell (in RHD car).

Unless you have a cornering light option, there's no dedicated fuse in the main fuse box for the lights - it's all done by SAM.

Oh, and I presume you didn't replaced the halogen bulbs with [cheap] LED ones - those will flash ...
Now, the proper ones won't, but we're not allowed to discuss this

 

[ZZZZ]

I live in Leatherhead in Surrey

It is more likely the problem is electrical, rather than mechanical, so perhaps a chat with Mark or George at Comand Online is the best way forward? They are in Lightwater.

 

[M80]

SAM is located behind the carpet to the front of passenger's footwell (in RHD car)

Is there possibility that there is water ingress, are the carpets wet?

 

[daibevan]

My lights came on when my front SAM got wet.

 

[ZZZZ]

Is there possibility that there is water ingress, are the carpets wet?

My lights came on when my front SAM got wet.

Excellent point!
I forgot about that - half of the electrical gremlins in this car all due to water drain under the cabin filter getting clogged up.
There's also a ground point, on the passenger side, front of the door frame, about 6" up off the floor, right behind the black flexible cover - if it gets wet, or corroded, it could cause multiple errors.