No Airbag Warning Lamp

No Airbag Warning Lamp

Inoperative lamp, lamp circuit or no ignition voltage to the diagnostics module

Normal Operation

The airbag warning lamp is designed to illuminate for approximately six seconds when the ignition is switched on. This period is allocated for satisfactory performance of the airbag system self test.

Note: The airbag warning lamp is driven by the instrument pack and not directly by the airbag diagnostic module.

The airbag diagnostic module requires an ignition supply to pin 1 to energise the airbag warning lamp circuit. If the warning lamp circuit is open, or the diagnostic module does not receive an ignition voltage at pin 1, the warning lamp will not illuminate.

Open circuit in the warning lamp supply, in conjunction with another system fault, will cause the diagnostic module to emit five tones every 30 minutes while the ignition is switched on. Repair the faulty circuit before further diagnosis.

Note: The diagnostic module will not emit the five tone signal if the warning lamp is open circuit and there is no system fault.

Possible Causes

Defective airbag warning lamp

Faulty wiring in the airbag warning lamp circuit

Loss of ignition voltage at diagnostic module pin 1.

Loss of ground at diagnostic module pin 3

Instrument pack fault

Fault Analysis

WARNING: Read and adhere to all warnings and safety procedures at the start of this section when working on the airbag system.

1. Remove the instrument pack and check the airbag warning lamp.

   If the lamp is good, go to step 2.

   If the lamp is defective, replace it, switch on the ignition and check that the lamp is now on for approximately six seconds after ignition on.

2. Disarm the airbag system and fit airbag simulators (6.4.21.4).

3. Connect the PDU. Switch on the ignition. Measure the 12V ignition supply voltage from airbag diagnostic connector pin 1-1 (+) to chassis ground. If ignition voltage is present, go to step 6. If ignition voltage is not present, go to step 4.
4. Check fuse F15 passenger side fusebox RHD or F17 passenger side fusebox LHD (ignition supply to the diagnostic module pin 1-1). If the fuse is good, go to step 5. If the fuse is replaced, go to step 6.
5. Check for an open circuit on the YW wire from fuse F15 passenger side fusebox (F17 LHD) to diagnostic module pin 1-1. If continuity is good, isolate the fault in the 12V supply to fuse F15 (F17) and then go to step 9.
6. Measure the voltage from diagnostic module pin 1-1 to diagnostic module pin 1-3. If 12V is not present, isolate and service the open circuit in the diagnostic module ground to pin 1-3. Then go to step 7.
7. Switch the ignition off. Set up to measure the voltage from DM pin 1-4 to DM pin 1-5 during the first six seconds after ignition on.

Switch on the ignition, the warning light signal to the instrument pack should switch for six seconds after a brief delay.

If the signal does not switch, the diagnostic module is faulty. Replace the module, switch on the ignition and check that the airbag warning lamp does light for six seconds after ignition on.

If the signal does switch for approx. six seconds after ignition on, the fault is in the instrument pack or wiring. go to step 8.

8. Check continuity of the YW wire from diagnostic module pin 1-4 to instrument pack 16 way plug pin 2.

If continuity is good, service the instrument pack and then retest to ensure correct indication from the airbag warning lamp at ignition on.

If continuity is defective, service the wire and then retest to ensure correct indication from the airbag warning lamp at ignition on.

9. Disconnect the PDU, and rearm the airbags (6.4.21.4). Switch on the ignition and check for correct indications from the airbag warning lamp.