Faulty Signal

DB1 Checking other Diagnostic Trouble Codes (DTCs):





- Ignition on.
- Read off diagnostic trouble codes (DTCs) in fuel/ignition system. Is the engine coolant temperature (ECT) sensor DTC stored?

Yes: DB2
No: DB3

DB2 Engine Coolant Temperature (ECT) Sensor Diagnostic Trouble Code (DTC):
Fault-trace according to the relevant fuel/ignition system information on ALLDATA.

DB3 Status Check:





- Ignition on.
- Go into scrolling values and read off engine coolant temperature (ECT). Does engine coolant temperature (ECT) gauge display -40 °C (-40 °F)?

Yes: DB4
No: DB9

DB4 Checking Engine Coolant Temperature (ECT) Sensor Signal:





- Ignition off.
- Connect the breakout box to the engine control module (ECM). (Fenix 5.2, Motronic 4.3, Motronic 4.4 or Diesel MSA 15.7) and check ground terminals according to the relevant ALLDATA section.
- Disconnect the engine control module (ECM).
- Ignition on.
- Connect a voltmeter to the breakout box as follows: # 23 (# B23) and # 28 (# B28) The voltmeter should read approximately 6 V.

If reading is OK: DB7
If value is lower: DB5
If value is higher: DB6

DB5 Checking for an Open-Circuit and Short-Circuit to Ground:





Check cable between combined instrument panel # A26 and engine control module (ECM) # B23. On cars with ECC: Check cable between combined instrument panel # A26 and ECC control module # C2 for a short-circuit to ground according to ZA3. Permanent Faults Then continue with DB8.

DB6 Checking for a Short-Circuit to Supply Voltage:
Check cable between combined instrument panel # A26 and engine control module (ECM) # B23. On cars with ECC: Check cable between combined instrument panel # A26 and ECC control module # C2 for a short-circuit to supply voltage according to ZA4. Permanent Faults Then continue with DB8.

DB7 Checking for Contact Resistance and Oxidation:
The cause of the DTC has been loose connections in the engine control module (ECM) connector. Check connector for contact resistance and oxidation and remedy according to ZA5. Permanent Faults Then continue with DB8.

DB8 Verification:





After carrying out the repair check that the fault has been remedied.

- Ignition off.
- Reconnect connectors, reinstall components.
- Ignition on.
- Go into scrolling values.
- Read off engine coolant temperature (ECT). Does engine coolant temperature (ECT) gauge display -40 °C (-40 °F)?

Yes: Fault corrected
No: Fault not found

DB9 Faulty Signal, Intermittent Fault:





- Check combined instrument panel connector A and engine control module (ECM) connector for loose connections according to ZB5, and contact resistance and oxidation according to ZB6.
- Check cable between combined instrument panel # A26 and engine control module (ECM) # C2 for an intermittent open-circuit according to ZB2, an intermittent short-circuit to ground according to ZB3 and an intermittent short-circuit to supply voltage according to ZB4.
- On cars with ECC: Check cable between combined instrument panel # A26 and ECC control module # C2 for an intermittent open-circuit according to ZB2, an intermittent short-circuit to ground according to ZB3 and an intermittent short-circuit to supply voltage according to ZB4.

For ZB1 - ZB6, Intermittent Faults