TL. MFI #21 No Main Relay Control Signal

TL. MFI #21

MFI#21 No main relay control signal




Fault message conditions:
The fault message is logged when voltage is above 3 V.

Causes of fault:
[1][2]System relay defective.
Break in engine GND.

Fault symptoms:
The engine will not start.
If the fault is intermittent the engine stops or runs rough.

TL1




Volvo ST, Test box
- Disconnect the ST in accordance with QA2. QA. Connecting The Volvo Scan Tool (ST)
- Connect the test box to MFI and check the GND points in accordance with P1-P2. P. Test Box, Signal Description
^ Continue with Checking the power supply TL2.

TL2




Checking the power supply
- Connect the control module to the test box.
- Install the fuse.
- Ignition on.
Connect a voltmeter between MFI#21 and MFI#5 (GND).
The voltmeter should read approx. 0.8 V.




- Try to start the engine.
The voltmeter should read approx. 0.8 V when the starter motor is operating or the engine is running.

If this value is OK
^ check the engine GND TL4.

If the reading deviates
^ check the [1][2]system relay TL3.

TL3




Checking the [1][2]system relay
- Try using a new [1][2]system relay.
Connect a voltmeter between MFI#21 and MFI#5.
- Try to start the engine.
The voltmeter should read approx. 1 V when the starter motor is operating or the engine running.

If this value is OK
^ the [1][2]system relay was broken.

If the value is still incorrect
^ check the engine GND TL4

TL4




Checking the engine GND
- Check the engine GND for breaks or loose connections in accordance with NA5. NA. Checking the Wiring

If the engine GND OK
^ try using a new control module.