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Ross, Diagnostic and repair technician
Category: Vauxhall
Satisfied Customers: 1183
Experience:  Licensed diagnostic and repair technician
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Omega 'V' 2.5. This is from a Diagnostic Technician of 50yrs

Customer Question

Omega 'V' 2.5. This is from a Diagnostic Technician of 50yrs exp. now semi retired, full diagnostics available, want suggestions as to what may be causing this car to have the engine management light on at all times. The car has been to various dealers and diagnostic specialists with the same results: ' There is nothing wrong with the car and everything is performing perfectly THIS LAMP liable to do this without fault being present on any other cars? and if so is it likely to be an ECU malfunction or is it an INSTRUMENT PANEL fault. Another fault has recently occurred, the tacho' and the speedo have recently stopped working.
Any suggestions?
Submitted: 2 years ago.
Category: Vauxhall
Expert:  Ross replied 2 years ago.
Hi my name is***** am a diagnostic technician and look forward to working with you.I will give a basic idea of the system and testing procedure, apologies if you already know much of this which you probably will but its easier for me to start from the very beginning.Both the engine ECU and Immob control unit have an input to the MIL Lamp, before going down the route of swapping anything there are a few tests you can carry out. It will require the use of a mulitmeter or volt meter, access to the ECU Terminals, and terminal removal tool for removing individual pins. The MIL light is permanently live from the instrument panel, and switched negative by the Engine ECU, and/or Immob control unit. (direct feed from immob to MIL light, and ECM tee's into the line from immob to MIL)The possibilities for the light being on with no specific reason will be either a short to + on the switched ground between the instrument panel and ECU/Immob controller, ECM/immob controller incorrectly setting the light or internal short to + within the Instrument cluster.Starting at the beginning we need to check to see where the ground feed is coming from. Access the connector on the Instrument cluster, there are two brown/blue wires, one is the MIL, the other is glow plug indicator.Access the ECU Connector (wire side plugged in) Pin 22 is the switched ground to the MIL on the brown/blue wireUse a continuity tester between the blue/brown at the instrument cluster and pin 22 of wire side of the ECU Connector to identify which of the two is the MIL, and which is glow plug. Once you identify the MIL feed, test for ground supply from pin 22, if there is a ground feed from the ECU, the ECU Is at fault. The wire should be disconnected from the connector on its own and tested by probing the disconnected blue/brown wire, If there is no ground feed on the wire when disconnected from the ECU, it confirms the ECU is switching ground for no reasonIf there is ground at the wire when disconnected from the ECU, the Immob controller or a short to + is the suspect. Again the blue/brown wire at the Immob controller can be pulled to see if this is causing it to switch to ground. If both ECU and Immob are NOT Switching the Blue/brown to ground, there is a wiring fault between the immob/ECM and the instrument cluster.I will attach some diagrams of the ECU Connector and some wiring diagrams to help make sense of it.
Expert:  Ross replied 2 years ago.
Wire diagram
Expert:  Ross replied 2 years ago.
ECM Pin location