Instrument Cluster / Carrier

B1720

Fuel gauge sensor

Fault symptoms
The fuel gauge shows tank empty.
The indicator lamp for low fuel level is on.
Some of the trip computer's functions are affected.

Condition
Break/short circuit in the fuel gauge sensor circuit.

Diagnostic help
The diagnostic tool can be used to obtain the following fuel level information:
- Fuel level sensor (shows fuel remaining in the tank through measuring voltage V across the fuel gauge sensor).
- Fuel level (shows remaining fuel in the tank, unit litres).
- Fuel level, filtered (shows remaining fuel in the tank, main instrument unit's internal filtered value).
The fuel gauge can also be activated with the diagnostic tool.

Check the wiring harness
Jiggle the wiring harness at several points and in different directions to detect intermittent breaks and short-circuits in the leads. Observe the multimeter, test lamp or diagnostic tool during the test.

Diagnostic procedure

1. Checking sensor ground
- Unplug connector: H4-18.






- Connect test lamp 86 11 857 to B+ and pin 3 of the fuel level sensor's male connector.






- The test lamp should light up.






Is the function correct?
YES
- Go to step 2.
NO
- Repair or replace the wiring harness between pin 8 (K12) of the MIU control module connector and pin 3 of the fuel level sensor connector.
- Go to step 5.

2. Checking sensor input
- Contact Main instrument unit.






- Read value: Fuel level.






- Value should be: 12 V.

Is the function correct?
YES
- Go to step 3.
NO
- Check and if necessary rectify the lead between pin 9 of the control module connector and pin 4 of the sensor connector.
- Go to step 5.

3. Checking sensor input
- Connect a jumper between pins 3 and 4 of the connector.






- Read value: Fuel level.






- Value should be: 0 V

Is the function correct?
YES
- Go to step 4.
NO
- Check and if necessary rectify the lead between pin 9 of the control module connector and pin 4 of the sensor connector.
- Go to step 5.

4. Checking the wiring harness
- Check the wiring between connector H4-18 and the fuel level sensor.






Is the lead OK?
YES
- Replace: Fuel level sensor
- Go to step 5.
NO
- Rectify the fault.
- Go to step 5.

5. Final check
- Clear the diagnostic trouble codes in all systems.






- Perform a functional test.
- Evaluate the function check.






- Check that no diagnostic trouble codes recur.






Has the diagnostic trouble code recurred?
YES
- See Fault diagnosis, general, "Before changing a control module." Before Changing A Control Module
NO
- The steps taken to rectify the fault were correct.