Test Notes

Fault Code 52-Backup Power Supply Voltage Boost Fault

Normal Operation

A backup power supply is contained within the air bag diagnostic monitor that consists of four capacitors and a voltage boost circuit. The voltage boost circuit charges the capacitors to 16-19 volts when the ignition switch is turned to RUN. The backup power supply is connected through a diode to pin 15 (circuit 611, W/O) of the air bag diagnostic monitor. The resistance of circuit 611 to ground is infinite since it is an open circuit. This open circuit allows the capacitor to maintain its higher voltage because there is no discharge path for the capacitor. The air bag diagnostic monitor measures the voltage on the backup power supply capacitors. If the voltage on the capacitors does not reach and maintain a minimum of 16 volts after approximately 30 seconds, the air bag diagnostic monitor will flash code 52 to indicate low voltage in the backup power supply voltage boost circuit.

Possible Causes

Low backup power supply voltage can be caused by:

1. Resistance on circuit 611 (W/O) to ground. Resistance to ground on circuit 611 or circuit 612 (P/O) will cause the backup power supply capacitors to discharge and the boost circuit will not be able to boost the voltage.
2. Boost circuit failure within the air bag diagnostic monitor. If the voltage boost circuit in the air bag diagnostic monitor is faulty it is unable to raise backup power supply voltage on the capacitor.