Air bag backup power supply replacement

[sly]

read this thread for the codes (needs stickied too)

backup power supply fault (I have code 52 on my vic now).

how does one replace the backup battery? Anyone know?

[miamibob]

Isn't that the "blue box" behind the Glove Compartment??? It has the capacitors that store power in case of a crash and the power is cut.

[86VickyLX]

Isn't that the "blue box" behind the Glove Compartment??? It has the capacitors that store power in case of a crash and the power is cut.

No. The backup power supply is located next to the EEC-IV computer, at least it is in the box. If the battery is dead, disconnect the battery. Give the system about 10 minutes, just in case. Then remove the back up supply. It just unplugs. Not too hard. Replace with another and power up the system (reconnect the battery). The fault should go away. As always, when you're doing this, be careful, and inspect the wiring, to make sure you don't have other issues.

[miamibob]

Had a '93 GM and if we are talking about the same unit it is behind the glove box (if the car in question is 93 or newer).

[86VickyLX]

Had a '93 GM and if we are talking about the same unit it is behind the glove box (if the car in question is 93 or newer).

To my knowlege, the Diag Monitor (the blue thing) and the back up supply are different.

[miamibob]

Wow, thought they were all included in the "blue box" behind the dash. When my Dad's car (a 1993) got an Air Bag Code that indicated the capacitors were bad (don't remember the code, though) I got a new box, installed it and that was it.

[sly]

I keep forgetting I have the service CD for 93-94 Ford cars. bah...

DIAGNOSTIC TROUBLE CODE 52

Back Up Power Supply Voltage Boost Fault

Normal Operation

A back-up power supply is contained within the diagnostic monitor that consists of 4 capacitors and a voltage boost circuit. The voltage boost circuit charges the capacitors to 16-19 volts when the ignition switch is turned to ON. The back-up power supply is connected through a diode to diagnostic monitor Pin 15 (Circuit 611, W/O). 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 diagnostic monitor measures the voltage on the back-up power supply capacitors. If the voltage on the capacitors does not reach and maintain a minimum of 16 volts after approximately 45 seconds, the diagnostic monitor will flash Diagnostic Trouble Code 52 to indicate low voltage in the back-up power supply voltage boost circuit.

Possible Causes

Low back-up 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 back-up power supply capacitors to discharge and the boost circuit will not be able to boost the voltage.

2. Boost circuit failure within the diagnostic monitor. If the voltage boost circuit in the diagnostic monitor is damaged it will not be able to raise the back-up power supply voltage on the capacitor.

Since I've had the safing sensor code before... I'll check the contacts on that again. May need a refresh.

[86VickyLX]

Well, that settles it, it's in the blue box. Just be sure when you replace it that it's the same part number. And you shan't go wrong. Just note you can't operate the car with that box disconnected.

[sly]

yeah... gonna have to troubleshoot the system though. It could just be the harness contacts in the safing sensor. This is gonna be a PITA.

[jcrules78]

Hey guys,
I have that air bag 52 code as well in my 97 GM. I just saw that the # 10 fuse was blown, so I replaced it. But it is still flashing me the 52 code. Is that blue box located behind the glove box in the 95-97 models too? Do you have to pull the glove box out to get to it?