How Do I Repair a Faulty Mercedes-Benz ECU?


G'day John,

As an avid fan of your segment on 2UE with Tim Webster every Sunday afternoon, I am hoping to obtain your advice concerning a Mercedes Benz Av190 automatic (2002 model with approx. 115,000km) which I purchased by auction a few weeks ago. Of course, I fully accept that there is always a risk in purchasing a car by auction due to an inability to perform a thorough check before the time of purchase.

I purchased the car unregistered for a little over $3000 (including auction fees), which seemed to represent good value. Soon after purchase I had some "routine" service work done (fluids, plugs, battery, two tyres, sway bar bushes, etc) for a reasonable price, and I have since obtained the necessary blue slip to enable registration with no problems at all.

However, when I picked up the car I immediately noticed that it had poor performance, and also that the "engine warning" light was on. My trusted mechanic has advised me (only after performing the above "routine" items, mind you) that this is due to the car being stuck in "limp home" mode, which is caused by a faulty "transmission selector module".

To rectify this fault, I have been informed that a new module will cost in excess of $3000!!! I have also been informed that a second hand unit will not suffice, because the module is suitable for a single vehicle use only. As I understand it, if a used module is simply transferred from one car to another, the computer becomes "confused" and it will not run at all.

John, may I ask if this scenario sounds reasonable to you? Obviously, I am looking for the required repairs to be completed for a minimal cost. Any advice you can provide will be greatly appreciated.

Kind regards,



G'day Robert,

What a brain bender. It took me a while to find a cheaper solution for you. (I'm assuming the faulty transmission electronic control unit, diagnosed by your mechanic, is the correct diagnosis of the problem. It sounds plausible. A defective transmission ECU could make the vehicle enter 'limp home' mode.)

Up front, $3000 to repair that vehicle is outrageous (on a $6500 car...) This component is a black box with some electronics inside, worth about $10. It's daylight robbery. An older (used) unit might confuse the system, but can probably be 're-flashed' or initialized in some way with the right tools.

The good news is that I found these guys: Australian ECU Repairs. They specialise 're-manufacturing' in the A & B class transmission ECU, among others. Give them a call and see if they can help you.

This was like finding a needle in a haystack. Or MH 370 in the Indian Ocean.

Thanks for listening on 2UE mate, and sorry for the delay in getting back to you - I've been swamped, and finding these guys took some digging.

Hope it helps.