Airbag DM Fault Code 52

Airbag DM Fault Code 52

Back-up power supply - voltage boost fault.

Normal Operation

A back-up power supply consisting of a capacitor and voltage booster is contained within the diagnostic module. The voltage booster charges the capacitor to 24 ± 1 volt when the ignition is on. The back-up power supply is connected to diagnostic module pin 1-9 via a diode. Since the resistance of pin 1-9 to ground is infinite, the capacitor has no discharge path and the back-up supply is maintained at a high voltage. The diagnostic module monitors this voltage and will flag a code 52 if a minimum of 23V is not achieved within 45 seconds of switching on the ignition.

Possible Causes

Low back-up supply voltage may be caused by:

• Partial or total short circuit of pin 1-9 to ground.
• Boost circuit failure within the diagnostic module.

Fault Analysis

1. Disarm the airbag system and fit airbag simulators (6.4.21.4).
2. Disconnect the diagnostic module. Check for a partial or permanent short circuit to ground from diagnostic module harness connector pin 1-9.

If no short circuit is detected, go to step 3.

If a short circuit is detected, service the wiring as necessary. Reconnect the diagnostic module. Clear the code 52. Rearm the airbags.

3. Using a high resistance digital multimeter, set up to measure the voltage from diagnostic module pin 1-9 to ground. Switch on the ignition.

If the voltage is in the range 24 ± 1 volt, the back-up power supply is good. Suspect an intermittent short circuit to ground and recheck the output circuit from pin 1-9.

If the voltage is below the range 24 ± 1 volt, replace the diagnostic module.

4. Rearm the airbags (6.4.21.4).

Airbag DM Fault Code 53

Internal diagnostic module failure.

Normal Operation

The diagnostic module constantly measures the voltage on pins 1-2, 1-6, 1-11 and 1-12. It should be 10 ± 1 volt. The voltage is regulated by a resistor within the diagnostic module and the resistance to ground of pins 1-2, 6, 11 and 12 should be infinite. The resistance across the normally open contacts of the crash sensors should also be infinite. If the resistance of the pins to ground or across the crash sensors becomes measurable, the voltage will drop. At between 5V and 10V the diagnostic module will recognise an internal voltage regulation failure and flag a code 53 fault and the airbag warning light will be illuminated.

A dead short to ground in the crash sensor circuits will drop the voltage below 5V and the diagnostic module will flag a code 14 fault.

The diagnostic module performs several self-tests as the ignition is switched on. If it fails any test, fault code 53 will be flagged.

Possible Causes

• A decrease in resistance from infinity between the primary crash sensor circuits and ground.
• An internal diagnostic module self-test failure.

Fault Analysis

1. Disarm the airbag system and fit airbag simulators (6.4.21.4).
2. Check each of pins 1-2, 1-6, 1-11 and 1-12 for continuity to ground.

If resistance of all circuits is infinity, go to step 3.

If any resistance other than infinity is detected, service the circuit wiring as necessary. Reconnect all connectors and switch on and clear all fault codes.

Switch off the ignition and then switch on again. Check that the airbag warning lamp comes on at 'ignition on' and extinguishes after approximately six seconds on satisfactory completion of the airbag system self-check.

3. Rearm the airbags (6.4.21.4).