How to: - Diagnose and repair Air Bag Code 33 | Ford Explorer - Ford Ranger Forums - Serious Explorations
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How to: Diagnose and repair Air Bag Code 33

kcblakely

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May 16, 2015
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City, State
Washington DC
Year, Model & Trim Level
2003 Ford Explorer Limite
Hi All: I got a lot of info off of this forum in addressing this and other issues on my GF's 2002 Explorer, so I thought I would try to pay back in a small way.

Problem: Airbag light on preventing inspection (not to mention danger of compromised restraint system)

The supplementary restraint system (SRS) is distinct from the other OBD systems on this and most older vehicles. It has it's own controller (the RCS: Restraint Control Module) and it throws its own codes that are typically NOT readable thru the OBD port. One reads the codes by counting flashes of the airbag light; when the ignition is turned to RUN, the airbag light will illuminate and then go off if all systems are good. If there is a fault, it will flash several times (in my case for the 2002 Explorer: 6), go dark for a few seconds and then flash to display the code. The airbag light will display the code by flashing a number of times for the first code digit, pausing, then a number of times for the second code digit, then pause several seconds, then repeat the process two more times, then stay lit. So you get three opportunities to read the code, and if you miss it, you can initiate the read again by simpy turning the ignition off, then back on.

Code 33 indicates a fault on the driver's side seat belt pretensioner: the module is unable to read voltage through the pretensioner circuit. Code 34 indicates a fault on the passenger side.

The seatbelt pretensioner is a cylindrical device that sits between the seat and the console, parallel to the seat, where the seatbelt latch is attached to the seatframe. It's purpose is to lock the seatbelt tight on the driver should there be an impact, preventing the driver from traveling too far forward and possibly being injured by the expanding airbag. The pretensioner is actually a small explosive device which should be handled with care, as should all components of the airbag system.

Under the driver's seat there are two wiring components dealing with the SRS. There is a two-prong white plug and a two prong yellow plug. Other connectors and wiring harnesses may be under there, depending on model, year and options, but these are the only two associated with the SRS. the white plug is a circuit that enables the SRS to know if the seatbelt is fastened, thus enabling it to "ding" at you if you drive unbuckled. If you disconnect the white plug and turn on the car, you will get code 51.

The yellow plug is the pretensioner circuit. A two-wire lead emerges from the larger seat harness (which also has all the wires for all the other stuff the seat does, like power controls and ***-warmers) and terminates at a male yellow plug. A female yellow plug goes from there to the pretensioner and plugs into the top of the pretensioner.

In almost all cases, a code 33 indicates a broken wire or short in the harness with the yellow plug, and this short or break will be in the only place where those wires are moving around a lot: under the seat.

Fixing a code 33 is pretty simple:
1. Remove the seat: four large bolts hold it to the floor of the car. Disconnect all wiring harnesses, including the yellow plug
2. Follow the yellow-plug wires and disconnect the plug from the pretensioner. Remove the resulting two-wire harness for testing.
3. Using a volt-ohmmeter, test connectivity thru the plugs. Obviously there should be max connectivity from end to end for each wire and no connectivity between the wires. NOTE that the plugs - at least the larger female yellow plug - will have a shorting bar in it! This is a safety feature that closes the circuit and (hopefully) prevents the pretensioner from deploying due to a random static charge while unplugged. In order to test these wires, you will need to un-deploy the shorting bar. if there's a short, find it and fix it. If there's a break, find it and fix it.
4. If the harness checks out, *closely* inspect the two-wire lead that emerges from the larger seat harness and terminates at the male yellow plug. Look for looseness indicating a broken wire under the insulation or any evidence of short. Peel back the the wrapping and harness casings as much as you think you have to. If there's a break, find it and fix it.
6. If you have not found an issue by now, you either have a bad pretensioner or there is a break/short somewhere else in the system.

For my part, I had a broken wire inside the insulation at step 4.

Hope this helps someone.....
 






96firephoenix

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March 14, 2015
Messages
646
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City, State
Indianapolis, IN
Year, Model & Trim Level
2002 Ford Explorer XLT
Bump. My 02 is throwing an SRS code for a pretensioner fault that I got off my code reader, but it didn't say on the code reader which one - I"m sure the code indicates it, but I didn't write it down. I'll check the light flashes tonight to see which one.
 






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