![]() ![]() Other ECU failures may rarely occur but they are much more unusual than those listed above.ĮCU Circuit Chip Failure Mode. Possible replacement units are 937 and 967. That one has a steady demand so failure must be fairly common, though not like the non-turbo counterparts as far as I can tell. The only turbo ECU that causes problems is the LH 2.4 563. Every one I have seen lately is a Fuel injection or Programma rebuild with the old Volvo ECU long dead. The LH 2.4 California emission with EGR 556 Volvo original must be atrocious too. The 16 valve ECUs 928, 571 seem to work fine in these cars too. ![]() I have never had a bad 951 that I can recall. However, I have had two white label 561s that failed recently so they are not a sure thing. The bad ones are all LH 2.4 including the 561, with few pink label ECUs surviving. This info is from pulling and running dozens of ECUs of each number discussed. If the car runs, then the ECU fuel pump control circuit is bad. IT IS NOT OK to continue to use the car with this fixed jumper feed to fuel pump. If car now starts and runs, take for road test to confirm OK (put on exhaust gas analyser first with catalyst equipped vehicles). This +12V jumper should make the car act like the fuel pump relay is ON. The 2 terminals are the nearest left and middle right pins on the relay board). Now take a small piece of wire to jumper terminals 30 and 87/2 on the relay board (the terminals are identified on the relay module pins). ![]() Diagnostic checklist: ACCURATELY Identify fuel pump relay and remove. Symptoms.No prior warning, car usually breaks down on road or fails to start when warm through loss of fuel pump relay control. ![]() This note is from Car Electronic Service in the UK and applies to: 1988 to 1992 740 and 740 GLE with Bosch Jetronic LH 2.4 fuel injection ECUs part numbers 590/591/594/595. Is the ECU is getting a signal from the ignition system? How about power from the ignition? Only after a complete diagnosis should you condemn the ECU. All grounds, power and sensor inputs should be tested at this plug before the ECU is condemned. Check all the sensor inputs to the ECU at the connector: you can remove the small screw and wire tie on the cover, pull it off, and remove the little "haircomb" plastic piece on the side which exposes all connectors without actually disconnecting the ECU itself. First check the fuel injection system and radio suppression relays. Multiple error codes, sometimes randomly generated, despite using known good sensors and components.ĮCU Diagnosis.Engine will not start, spark plugs are dry and the ignition system produces spark.The engine will not rev higher than 3000 RPM.No fuel pump operation, butthefuel pump operates when its relay is jumpered between pins 30 and 87/2.Air-fuel mixture is too rich (this can damage catalytic converters).See also Engine Failure/No Start: Bad ECUĬommon symptoms of a failing LH injection module: VOC Home | FAQ Home Fuel Injection and ECUsħ60T Engine Stops Dead at 60MPH Bad Power Stage ModuleĮCU = Engine Control Unit computer (either fuel injection or ignition) ![]()
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