This family of ABS ECU's, denoted C type, have common characteristic in the diagnostic element of their design. This is that once they have been communicated with diagnostically and then put to sleep they inhibit the communication with other ECUs sharing the same data bus and even with themselves. To re-establish diagnostic communication, the ignition must be turned off for approximately five seconds.
It is only possible to communicate with the ABS ECU when the system is in its idle state, that is with the ignition on and the engine running or not. Once the ECU has detected a signal from all sensors that indicates each one has exceeded 2km/h the ECU turns off the dash lamp and exits diagnostic mode. All ECU resources are then used to monitor the sensors and diagnostic communication is no longer possible until the ignition supply has been disconnected and then re-connected.
Despite sharing a common communication standard which means they all start communicating the same, and share some very basic features, these ECUs are actually laid out very differently in respect of their memory usage meaning codes read from one ECU with the wrong program may give incorrect meaning and other codes may not be shown. Also some of them actually require each memory location used for the fault code storage to be re programmed to 0 individually. This means that using the wrong module on an ECU can alter the ECU and make it non functional, re using the right module after will not correct this. So although the ECUs look identical to that used in other vehicles of the same age and can be plugged in, they are NOT diagnostically interchangeable.
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For more detailed information about this ECU please click here.