Fault Code 21 Impact Sensor Incorrectly Mounted to Vehicle

FAULT CODE 21
Safing Impact Sensor Incorrectly Mounted to Vehicle

Normal Operation
The Air Bag Diagnostic Module (DM) monitors the resistance value between pins 16 and 3. If a resistance value of greater than 2.0 Ohm is detected the MIL Lamp will illuminate and fault code 21 will be present, indicating incorrect mounting of the safing impact sensor. Secure connections to ground at both the sensor case and the vehicle are necessary to avoid this fault.

Possible Causes
- Poor or dirty connection between safing sensor case and vehicle ground.
- Poor or dirty termination at safing sensor internal ground.
- Open circuit on wiring between DM pin 16 and safing sensor ground terminal.

Fault Diagnosis
1. Resistance - check
- Disarm Airbag/SRS system.
- Disconnect battery ground lead.
- Measure resistance between pin 3 (ground) and pin 16 (ground - safing sensor).
- Is resistance value greater than 2 Ohm?

No - Proceed to step 2.
Yes - Renew DM.

2. Sensor ground - check
- Disconnect safing sensor from harness.
- Measure resistance between sensor pin 5 and sensor mounting (chassis ground).
- Is resistance value greater than 2 Ohm?

Yes - Proceed to step 3.
No - Examine wiring between internal sensor ground and harness connection 10. repair faults as necessary.

3. Sensor mounting - check
- Remove safing sensor from mounting.
- Clean all mounting surfaces thoroughly and refit sensor.
- Re-test resistance between harness connection 10 and sensor internal ground.
- Is resistance value greater than 2 Ohm?

Yes - Renew sensor.
No - Refit sensor and connect harness and battery ground lead.

4. On completion
- Arm and verify the Airbag/SRS system.

Electrical Schematic-Safing Impact Sensor Incorrectly Mounted To Vehicle, Fig.1:

1. Instrument Panel Fuse
2. Engine Compartment Fuse
3. Safing Sensor
4. Cable Reel Cassettes
5. Driver-side Airbag
6. Passenger-side Airbag
7. RH Impact Sensor
8. LH Impact Sensor
9. Airbag MIL Lamp
10. Diagnostic Module