TideLog Posts Tagged “CAN”

If you’re driving along and suddenly the “Check Diagnostics for Engine ECU at next stop” message appears in the dash infopanel, along with the CHECK indicator and the temperature gauge reading cold or just above cold, the engine temperature sensor has failed or is dirty and will need to be replaced.

Units Involved

The Engine ECU (EECU) and the Vehicle ECU (VECU) are involved in this process. The Engine ECU periodically checks the temperature sensor. The resistance readings are sent as a changing signal to the dash temperature tacho needle as the temperature decreases or increases, the signal power varies the needle position. After 5 or 10 minutes from cold start the engine ECU knows that the engine should be warm, so if it starts to get a completely cold reading after this time, sends a signal via the CAN (Controller Area Network) to the VECU which displays a message in the dash infopanel.

Cause Elimination

This fault should not be deemed to be the temperature sensor if only the temp needle is too low. The CHECK light and message MUST also be displayed. Otherwise, the tacho needle must be checked, and/or the signal from the VECU.

To check if the needle is faulty, turn off the bus engine and ignition completely, turning the starter to 0. Turn it to I to switch on the ignition and the needles should all do a full sweep of their dials to the right then return back to the left. Turning the starter to II will start the engine, all fuel and air dials should go to their operating positions, showing the correct fuel and air pressures. To check the turbocharger boost needle you will need to drive the bus on hard acceleration on a straight road. It will not move if the footbrake or airbrake is applied as the turbo only operates when the bus is moving in gear.

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