Cellular Phone Microphone: Testing and Inspection

Fault symptoms
Microphone does not work.

Fault diagnosis
Note that the microphone has a high-level and low-level output. Connecting the wrong microphone output can overdrive the unit or give too low a signal level.

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

Diagnostic procedure

1. Check the lead between the microphone and the main unit
- Unplug connector: Connection, mobile telephone: (375).






- Unplug connector: Microphone, roof console: (634).






- Take a resistance reading.
- Red test lead: Microphone, roof console: 3.






- Black test cable: Connection, mobile telephone: 3.






- The reading should be 0 ohms - 1 ohm.

Test results OK?
YES
- Go to step 2.
NO
- Rectify the lead between pin 3 in the microphone's female connector and pin 3 in the mobile telephone connection.
- Go to step 8.

2. Check the lead between the microphone and the main unit, continued
- Take a resistance reading.
- Red test lead: Microphone, roof console: 2.






- Black test cable: Connection, mobile telephone: 10.






- The reading should be 0 ohms - 1 ohm.

Test results OK?
YES
- Go to step 3.
NO
- Rectify the lead between pin 2 in the microphone's female connector and pin 10 in the mobile telephone connection.
- Go to step 8.

3. Check the lead between the microphone and the main unit, continued
- Take a resistance reading.
- Red test lead: Microphone, roof console: 1.






- Black test cable: Connection, mobile telephone: 9.






- The reading should be 0 ohms - 1 ohm.

Test results OK?
YES
- Go to step 4.
NO
- Rectify the lead between pin 1 in the microphone's female connector and pin 9 in the mobile telephone connection.
- Go to step 8.

4. Check the lead for short-circuiting to ground
- Take a resistance reading.
- Red test lead: Microphone, roof console: 3.






- Black test lead: vehicle battery: B-.






- The reading should be infinity.

Test results OK?
YES
- Go to step 5.
NO
- Rectify the lead between pin 3 in the microphone's female connector and pin 3 in the mobile telephone connection.
- Go to step 8.

5. Check the lead for short-circuiting to ground, continued
- Take a resistance reading.
- Red test lead: Microphone, roof console: 2.






- Black test lead: vehicle battery: B-.






- The reading should be infinity.

Test results OK?
YES
- Go to step 6.
NO
- Rectify the lead between pin 2 in the micro- phone's female connector and pin 10 in the mobile telephone connection.
- Go to step 8.

6. Check the lead for short-circuiting to ground, continued
- Take a resistance reading.
- Red test lead: Microphone, roof console: 1.






- Black test lead: vehicle battery: B-.






- The reading should be infinity.

Test results OK?
YES
- Go to step 7.
NO
- Rectify the lead between pin 1 in the microphone's female connector and pin 9 in the mobile telephone connection.
- Go to step 8.

7. Checking the handsfree unit
- The fault is not in the car's wiring harness.
- Check the handsfree unit and leads as described by the supplier of the handsfree unit.






Test results OK?
YES
- Replace: Microphone, roof console.
- Go to step 8.
NO
- Repair or replace the handsfree unit.
- Go to step 8.

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






- Carry out a function check.






Test results OK?
YES
- The steps taken to rectify the fault were correct.
NO
- The fault has not been rectified.
Recheck:
- Leads between the handsfree unit and the microphone.
- Microphone, roof console.
- Handsfree unit.