Signal Missing

HB1 Checking other Diagnostic Trouble Codes (DTCs):





- Ignition on.
- Read off diagnostic trouble codes (DTCs) in fuel/ignition system. Is an engine speed (RPM) sensor signal diagnostic trouble code (DTC) stored?

Yes: HB2
No: HB3

HB2 Engine Speed (RPM) Sensor Signal Diagnostic Trouble Code (DTC) Stored:
Fault-trace according to ALLDATA for the relevant fuel/ignition system.

HB3 Checking Transmission Speed Signal:





- Start engine.
- Go into scrolling values and read off engine speed (RPM). Is the engine speed (RPM) within its permitted range?

Yes: HB11
No: HB4

HB4 Checking Warning Lamps:





NOTE: The combined instrument panel uses charging signal D+ as a reference for the engine speed (RPM) signal.

- Ignition on.
- Check that warning lamps light. Do they?

Yes: HB6
No: HB5

HB5 Checking for an Open-Circuit:





Check cable between combined instrument panel # A13 and generator (GEN) terminal D+ for an open-circuit according to ZA2. Permanent Faults Then continue with: HB10

HB6 Checking Engine Speed (RPM) Signal Voltage:





- 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: # 21 (# B21) and # 28 (# B28). The voltmeter should read approximately 6 V.

If reading is OK: HB9
If value is lower: HB7
If value is higher: HB8

HB7 Checking for an Open-Circuit and Short-Circuit to Ground:





Check cable between combined instrument panel # A11 and engine control module (ECM) # B21 for an open- circuit according to ZA2 and a short-circuit to ground according to ZA3. Permanent Faults Then continue with HB10.

HB8 Checking for a Short-Circuit to Supply Voltage:
Check cable between combined instrument panel # A11 and engine control module (ECM) # B21 for a short- circuit to supply voltage according to ZA4. Permanent Faults Then continue with HB10.

HB9 Checking for Contact Resistance and Oxidation:
The cause of the diagnostic trouble code (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 HB10.

HB10 Verification:





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

- Ignition off.
- Reconnect connectors, reinstall components.
- Start engine.
- Go into scrolling values and read off engine speed (RPM). Is the engine speed (RPM) within its permitted range?

Yes: Fault corrected
No: Fault not found

HB11 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 # A11 and engine control module (ECM) # B21 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 steps ZB1-ZB6, Intermittent Faults