I recently bought a new (to me) '96 F150 4x4 w/ 4.9L and E4OD. The airbag light is flashing 5 times, then once. Can anyone tell me what this means. Thanks!!!

 

Code 51 is a Diagnostic Monitor internal thermal fuse blown due to a short to ground.
To work on this circuit, the battery must be disconnected for at leat 15 min to drain the backup supply capacitor.
Use no meter testing on the bag circuit or you will blow the bag.
Be very carefull what you do when the system is powered up, around the sensors etc for obvious reasons.

 

So this is an airbag circuit problem? What can I do to diagnose and repair this? Is there a schematic in a haynes manual? Any advice would be very appreciated!!!

 

The only good service info would in the factory info.
These systems involve to much liability to be serviced by the average owner unless you have knowledge and background.
I don't know if the module can be repaired but the ground has to be found or a new module will suffer the same fate.
Good luck with it. May be dealer time on this one.
Sorry.

 

Code 51 means you need a new module AFTER you've found & fixed the problem that triggered it (which is most likely a bad clock spring). Look thru these pics & diagrams for plenty of info about your column - it's identical. If you can't find one locally at a reasonable price, I have a good used ADM from a '96 Bronco. E-mail me by clicking my username.



Note that it's perfectly safe to just unplug the airbag immediately after turning the key off, or any time the key is off. The shorting bar in the connector (green in this photo) is designed to prevent it from triggering even before the connector is fully separated. Just store any airbag face UP under the vehicle.



Here's the full text about LFC 51:

Air Bag Diagnostic Monitor Internal Thermal Fuse -- Fuse Blown Due to Intermittent Short to Ground (Code 51)


Normal Operation

Note: The air bag diagnostic monitor contains an internal thermal fuse that is not serviceable. The thermal fuse is controlled by a computer inside the air bag diagnostic monitor. The computer will open the thermal fuse whenever a short on the deployment circuits occurs. The thermal fuse does not open because of excessive current flowing through it. DO NOT attempt to jump out the thermal fuse with a circuit breaker or any other type of fuse.

Note: DO NOT install a new air bag diagnostic monitor until the cause of code 51 has been located and corrected. If a short to ground has not been located and repaired, the short is intermittent and IS NOT PRESENT AT THIS TIME. Installing a new air bag diagnostic monitor with an intermittent short in the system will result in repeat blown thermal fuses and repeat repairs.

The air bag diagnostic monitor measures the voltages at the air bag diagnostic monitor connector pins. When certain air bag deployment circuits are shorted to ground, the system may become susceptible to unwanted deployment of the driver side air bag module. The air bag diagnostic monitor will sense a short-to-ground on any air bag deployment circuit and if a short is detected, will open the air bag diagnostic monitor's internal thermal fuse. Blowing of this fuse removes all power from the air bag deployment circuits. While the short to ground exists, the air bag diagnostic monitor will flash Diagnostic Trouble Code 13 or 14 depending where the short is. If the short to ground is intermittent and temporarily corrects itself, the air bag diagnostic monitor will flash DTC 51.

If the short to ground returns, the higher priority DTC 13 or 14 will be flashed instead of DTC 51. The air bag diagnostic monitor senses a short to ground on any of these circuits and helps to prevent unwanted air bag deployment by opening the air bag diagnostic monitor's internal thermal fuse.

If the air bag indicator is flashing DTC 51 and a short to ground has not been serviced, this means an intermittent short to ground exists in the air bag system. The air bag diagnostic monitor should only be replaced after service of the short to ground has been completed.

Some service tips for finding an intermittent short to ground follow:

 

Full text of 1996 Airbag LFC 51 (continued)

Note: Diagnostic Trouble Codes 13, 14 and 51 may be caused by the following conditions.

Note: DTC 51 resulting from water entry into the air bag diagnostic monitor may cause a backup beep sound to be heard as well as a flashing warning lamp. This is a nonlegitimate code.

Water/liquid may have entered the air bag diagnostic monitor.
* Cleaning of vehicle interior (spraying water on rubber mats or carpet cleaning). Look for water/mud spots on the air bag diagnostic monitor case and surrounding area.
* Application of Armor-All, or similar product, to the instrument panel (04320) or rubber floormat or spraying air-freshener under the instrument panel. Check for an oily residue on the air bag diagnostic monitor case.
* Condensation from air conditioner operation may have collected on the duct work under the instrument panel, dripped onto the buzzer/chime module mounting bracket, then into the air bag diagnostic monitor. Look for rust, white residue (corrosion) or water spots on the buzzer/chime warning module.
* Condensation may have formed in the air bag diagnostic monitor due to humidity in the air during A/C operation.

Note: Before proceeding, look for water spots on the inside of the air bag diagnostic monitor case and look for milky-colored corrosion spots (may be small) on the printed circuit board and/or the components in the air bag diagnostic monitor.

If it has been determined that water, liquid or condensation has contaminated the air bag diagnostic monitor, but not from any of the above sources, check the following sources of contamination:
* Water leak at cowl weld seam.
* Water leak at windshield.
* Water/mud may have splashed into the air bag diagnostic monitor from the floormat or carpet.
* Liquid may have spilled on the instrument panel, (above the radio). The radio or keyless entry may also be affected.
* Water leak at the radio antenna grommet. The water will travel along the antenna lead, then drip onto the air bag diagnostic monitor.

Note: When water testing the vehicle for a windshield or cowl seam leak, the water running off the windshield may not contact the cowl seam. If no leak is detected at the windshield, remove the cowl top panel and direct the water into the cowl and at the seam.

If water/moisture has contaminated the air bag diagnostic monitor, the source of the contamination must be identified. If the contamination is the result of a water leak, water test the vehicle and repair the leak as required.

Check the following locations for shorts to ground:
* Check for damaged crash sensor wiring.

Note: One side of the front air bag sensor and bracket (primary crash sensor) is grounded by design. The gray air bag diagnostic monitor harness connector contains a shorting bar inside the connector that will short Pins 2 and 3 together whenever the air bag diagnostic monitor is connected. Since Pin 3 is ground, shorting Pin 2 to 3 will cause a short to ground on both Pins 2 and 17. Make sure the red plastic locking wedge is removed from the gray connector before checking resistance of these circuits to ground.

Check resistance on front air bag sensor and brackets. Resistance should be infinite.
* Check for damaged shorting bars inside the gray diagnostic monitor connector.
* Check for damaged wiring (small nicks or cuts) on the back side of the driver side air bag module.
* Check the air bag sliding contact wiring down the steering column past the connector into the wire harness for damage.
* Check for damaged wiring at fuse block mounting bracket.
* Check for chafed wiring at the clutch pedal return spring (if so equipped).
* Check for damaged wiring between the air bag diagnostic monitor and the right cowl side (The wiring may have been damaged by the attaching screws under the glove compartment).
* Check rear air bag sensor and bracket (safing sensor) wiring behind the RH kick panel for damage or signs that water may have entered the connector (a water leak at the radio antenna grommet may result in water in the connector).
* Check the rear air bag sensor and bracket (safing sensor) wiring harness under the RH scuff plate. Remove the harness from the trough and check for foreign objects such as sheet metal screws, small pieces of metal or other sharp objects that may damage the wiring (the installation of running boards or similar equipment along the passenger door opening may result in damage to the wiring. Wiring may be damaged at the passenger's shoulder safety belt floor anchor located to the rear of the scuff plate.
* Check wiring to the rear air bag sensor and bracket (safing sensor).
* Check for water entry into the rear air bag sensor and bracket (safing sensor) connector. Water leaks at the rear window may result in water in the connector.
* Check dash panel connector for water or signs that water may have entered the connector.
* Check for loose or damaged pins or terminals.

 

Full text of 1996 Airbag LFC 51 (continued)

* Wiring may be damaged at or behind the large aluminum reinforcement located under the instrument panel at the left cowl. Pay particular attention to the following three locations:

-- At the base of the reinforcement (inspect this area for damaged wire(s) that may be visible without removing the reinforcement).

-- Wiring may be pinched behind the reinforcement (remove reinforcement).

-- The wiring may have been pinched between the reinforcement and a bracket that is welded to the dash panel (01610).

Repair Procedure

Should wiring require servicing, repairs may be completed as follows:
* Deactivate the air bag system. Refer to «Deactivate System» in the Glossary in the Diagnosis and Testing portion of this section.
* If wiring insulation is chafed or nicked exposing bare wire, wrap affected area(s) with vinyl electrical tape.
* If wire(s) are only nicked, wrap affected area(s) with vinyl electrical tape.
* If wire(s) are cut, refer to «Damaged Wiring» in the Parts Replacement portion of this section.

When repairs are completed, the following procedures should be followed to reduce the possibility of a recurrence of a short to ground in the area(s) repaired.
* Remove any existing burrs or sharp edges from metal surfaces that may come in contact with the repaired wiring.
* Apply ordinary cloth tape to these areas.
* Make sure wiring retainers are in the proper retaining holes.
* Use an appropriate wiring retainer to pull wiring away from metal surfaces.
* Replace the air bag diagnostic monitor. Refer to «Diagnostic Monitor, Air Bag», in the Removal and Installation portion of this section.
* Reactivate the air bag system. Refer to «Reactivate System» in the Glossary in the Diagnosis and Testing portion of this section.

CAUTION: Connect the Rotunda Air Bag Simulator 105-00010 or equivalent to the air bag system before system proveout is performed.

Perform the system proveout as follows:

Turn key from OFF to RUN and visually inspect the air bag warning indicator. The air bag warning indicator will light continuously for approximately 6 seconds and then turn off.

If an air bag system fault is present, the air bag warning indicator will either fail to light, remain lit continuously or flash after proveout. The flashing may not occur until approximately 30 seconds after the key has been turned from OFF to RUN. This is the time required for the air bag diagnostic monitor to complete testing of the system.

If the air bag warning indicator is inoperative and an air bag system fault exists, a tone will sound in a pattern of five sets of five beeps. If this occurs, the air bag warning indicator will need to be serviced before further diagnosis can be done.

When testing has been completed, deactivate system. Refer to «Deactivate System» in the Glossary in the Diagnosis and Testing portion of this section. Remove Rotunda Air Bag Simulator 105-00010 or equivalent.

Reactivate system. Refer to «Reactivation» procedure in the Diagnosis and Testing portion of this section.

Code 51 After Air Bag Deployment
Occasionally, immediately after an air bag deploys, the internal wiring of the driver side air bag module may become shorted to the metal housings of the driver side air bag module. This internal short is detected by the air bag diagnostic monitor as short to ground in the air bag deployment wiring. Since the air bag diagnostic monitor is still operating immediately after most deployments, the air bag diagnostic monitor will detect the shorted wiring and will flash Code 13 and blow the internal thermal fuse. After the deployment, as the air bag cools off, the internal shorted wiring may correct itself, therefore the short to ground will no longer exist and the air bag diagnostic monitor will flash Code 51. If a vehicle with a deployed air bag is flashing Code 51, inspect and replace all the damaged areas of the vehicle with crushed wiring, sensors, etc. If no damage is found assume that the deployed air bag was the cause for the intermittent short and replace the air bag diagnostic monitor when the new driver side air bag module is installed.

Note: Air bag diagnostic monitors can withstand several air bag deployments and do not need to be replaced after every deployment. Only replace the air bag diagnostic monitor if it is damaged.

 

Full text of 1996 Airbag LFC 51 (continued)

Code 51 Sequence of Events

1. Short to ground occurs on one or more of the circuits shown in heavy lines in the schematic.

2. The air bag diagnostic monitor recognizes the shorted wiring and flashes out a Code 13 or 14 and sends a signal to the internal thermal fuse, causing it to blow.

3. The air bag diagnostic monitor will continue to flash Code 13 or 14 while the short to ground is present. If the short to ground goes away, Code 51 appears.

4. The air bag diagnostic monitor only flashes a Code 51 when the thermal fuse is blown and the short to ground is not present. Do not replace the air bag diagnostic monitor until the short to ground has been located and serviced. Refer to the following diagram.



End

 

I bet the short is somewhere in the steering column. I'm getting ready to go to Africa on a 6 month deployment, so I'm just gonna mess with it when I get back, but the info is greatly appreciated. Is there a way I can print this info off, or will these pages still be here in August when I get back?

 

They'll still be here, and you can add this thread to your favorites, both in your web browser & here on the BBS, to make it easier to find again.

But you can also select the text, copy it, & paste it into a document editor (like Word or Notepad), then save it on your puter. My diagrams are stored on SMN, so just save my signature link as a browser favorite.