Hello,

I have a 1994 Ford Aerostar 2WD 4.0L with 120k miles on it. I had the airbag light start flashing approximately 2 months ago, with a code 51. After researching some this indicates the thermal fuse in the airbag module was blown and there is possibly an intermittent short or the clock spring is bad. I changed out the clock spring module because this seemed to be the most likely candidate, and put a working air bag module in it.

Fast forward a couple of months, and the air bag light is back on, flashing code 51 again. The cruise control and horn still work fine, so the clockspring is not likely bad. I have not been able to find anything really specific for code 51 as to where to look for possible shorts in the wiring harness. I did some searching this past weekend on the car where wiring passes through the body and did not see any bare wires. Can anyone provide any further insight into how to troubleshoot code 51 on an Aerostar?


Thanks!!

 

OBDI code 51 Diagnostic Monitor Internal Thermal Fuse Open

Description

Diagnostic monitor measures voltages at diagnostic monitor terminals. When certain air bag deployment wires are shorted to ground, system may become susceptible to unwanted deployment of air bag. Diagnostic monitor senses a short to ground and helps prevent unwanted air bag deployment by blowing diagnostic monitor thermal fuse. Blowing this fuse removes all power (battery and back-up power) from air bag deployment circuits. If short to ground exists, diagnostic monitor will flash Code 13. If short to ground is intermittent and temporarily corrects itself, Code 51 will flash. If short to ground returns, Code 13 will flash instead of Code 51. If Code 51 is flashing and short to ground has not been repaired, an intermittent short to ground exists in air bag circuit. DO NOT replace diagnostic monitor unless short to ground has been located and repaired.

Possible Causes

Code 51 will set if there is a short to ground in circuit No. 623, 614, 615, 617, or 619. A deployed air bag may also cause a Code 51 to set. When air bag deploys, internal wiring of air bag may become shorted to metal housing inside of air bag.

Check For Short To Ground

Inspect circuits No. 623, 614, 615, 617 and 619 for short to ground. Inspect wiring harness areas where wires pass through or are located next to metal components. Repair as necessary. After repair is completed, check AIR BAG warning light for codes. If Code 51 exists, deactivate air bag system.

Replace diagnostic monitor.

NOTE: Code 51 is displayed whenever diagnostic monitor thermal fuse is open and no other higher priority faults exist. Code 51 is normally seen after service of a Code 13 condition. If a Code 51 exists and a Code 13 condition has not been serviced, an intermittent short to ground exists in air bag deployment wiring. Intermittent short to ground must be located and serviced before servicing a Code 51 condition.

Hope this information helps...