I was wondering if its possible for a Mazda 3 2011 AT car to function without ECU? The reason I am asking is

  • When I start the engine, the CheckEngineLight doesnot come at all
  • When I took my car for scanning, they informed me that Port has been disconnected, and they assumed that ECU has been removed

I am taking my car to Mazda service tomorrow for a through check however if the ECU is to be replaced what is the cost am I looking at?

Also is AT sensor somehow connected to ECU or is it a separate one, the reason being when when I move the key to second position the AT light appears and disappears after the engine is started.

My Car Specs are Mazda 3 1.6 Gasoline AT 2011

  • Have you just purchased this car? It sounds like someone is trying to hide something. Does the car have VIN numbers on the body?
    – HandyHowie
    Commented Jan 12, 2016 at 12:38

2 Answers 2


There is no way a 2011 car can run without the engine ECU, unless the engine has been swapped for something from 70s.

  • Thanks @HandyHowie I have going thru a series of articles online, and they are very confusing, I will be visiting Mazda tomorrow, but my worry is scan port being disabled. I have bought this car second hand around 5 months back, and the AT shift from first to second gear is really worrying me, hence I went for a scan where I was given above outcomes. Commented Jan 12, 2016 at 12:42

In addition to the port being disconnected it is possible that the CEL bulb in the instrument cluster has blown, which would explain why you are not seeing it light up when the key is turned to Ignition On.

The transmission control module is usually separate from the engine control module.

  • Thanks @zaid, is there any other means to disconnect the same (More difficult to trace may be). Also I assume port disconnect and CEL bulb replacement is an easy kill. Commented Jan 12, 2016 at 13:11

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