After several blissful years with the SRS light staying dark, it began coming on consistently a while back. I don’t drive my truck very often, so I didn’t dive into it until this week.

I’ve read the codes several times using the Hawkeye, and confirmed the fault is always a driver airbag open circuit.

After disconnecting the battery and waiting a while, I removed the console, removed the connector from the SRS DCU (Diagnostic and Control Unit), and then removed, cleaned and reinserted the two wires for the driver airbag circuit. I plugged in the connector, connected the battery, and turned the key to Position II. After the pre-check, the light returned.

After again disconnecting the battery, I removed the driver airbag and tested continuity of the wiring to the DCU and that checked out okay. I then jumpered the driver airbag connector with a paper clip wire (pictured), reconnected everything else, and turned the key to Position II. After the pre-check, the light stayed off. Hooray!!! That indicated the problem must be with the airbag itself. But …

I confirmed from the RAVE that in the DII, during the pre-check the DCU tests continuity of the two airbag circuits and the two pretensioner circuits. According to the RAVE, the DCU does not test for any particular resistance value.

Given that, I tested continuity for the airbag itself. It passed. I have a spare airbag, so while I was at it I tested its continuity too. It too passed.

But, when I plugged in the airbag, reconnected the battery and turned the key, the SRS light came back after the pre-check. Same thing when I swapped in the second airbag. Arghh!!!

Every component in the system checks out individually, and the circuit is good when jumpered at the airbag connector, but when I put it all together there’s still a fault.

What can I be missing?

 

I had a similar problem on a Jeep Wrangler. It turned out to be that the ground for the airbag was bad. Might be worth checking out?

 

I also had a similar issue. Passenger side airbag fault. I disconnected and reconnected the connector and the fault went away for a couple of weeks. I replaced the airbag with a used one and the fault went away for a few months. I dis and reconnected the connector again and I haven’t got the light back for almost a year now. It seems that the connections are very finicky.

 

Part of our training as techs was to be careful about spreading the pins apart in connectors when putting jumpers in them. We were actually trained to never jumper a pin, but to pierce the wire shielding with a T-pin to probe them. What you are describing, is exactly why I assume they taught us that. I would like to think if you were able to get the terminals in the connector tightened back up, maybe it'd help fix your problem? Good luck

 

I’m happy to report that the problem appears to be solved.

In the end, it seems the driver airbag fault was caused by the connector from the SRS harness to the rotary coupler, which is located behind the black panel below the steering wheel.

That was the ONE connector I hadn’t checked and cleaned previously. It’s analogous to what many others have written in other forum threads about SRS pretensioner faults being remedied by simply unplugging and reconnecting the SRS connectors under the seats. In addition to disconnecting and reconnecting, I also cleaned it using CRC QD Electrical Contact Cleaner and a pipe cleaner. Doing that solved the problem.

But before getting to that connector, I did a lot of diagnostic work and I’d written up much of that work earlier, so rather than letting that work disappear, I'll go ahead and share it here.

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First, thanks to Mntnceguy. I wondered the same thing a few days ago, that is, did inserting the paper clip mess up the airbag connector?

To test that, I removed the two driver airbag wires from the DCU connector and clipped the leads from my multimeter onto them. I plugged the airbag into the connector to test continuity. The test confirmed continuity to, through and from the airbag. The meter read 8.3 ohms.

Having confirmed continuity of the complete driver airbag circuit, I put the driver airbag wires back into the DCU connector, reconnected the battery, and turned the key to Position II. Once again, the SRS light came back on after the pre-check. Still no success, even though continuity in the circuit is confirmed.

When earlier I jumpered the airbag connector to confirm continuity and the SRS later stayed off after the pre-check, the meter read 6.1 ohms. It was immediately after that that and the SRS light remained off after plugging the connector into the DCU and turning the key to Position II. That may indicate that although the RAVE says the DCU tests continuity only, it may also be looking for a resistance level less than the 8.3 ohms I found for the installed airbag and wiring. [Confirmed empirically; see below]

I also metered the two driver airbag wires individually. The R wire (-) read 2.5 ohms to the airbag connector. The RY wire (+) read 5.3 ohms. When I metered the airbag itself it read 2.5 ohms. I know that adds up to 10.3 ohms, but I wonder[ed] if the higher reading of the RY wire indicates greater resistance in the rotary coupler for the positive connection. [Note. It turned out the greater resistance was due to the rotary coupler connector, as noted above.]

That made me want to try swapping in a different rotary coupler, but new ones are $400+, and this is one instance where a used part may have the same problem.

So before going that route, I decided to look more carefully into the rotary coupler, and that led me to the connector that was apparently the problem.

As I suggested above, although the RAVE says the DCU tests continuity, with no mention of target resistance levels, my data seems to confirm it does so by “looking for” resistance below a threshold level (something between 5.5 ohms and 8.3 ohms; see data below). So even though the circuit always had continuity, the resistance level triggered the fault.

Here are the readings from my testing.

• R wire only - 2.5 ohms
• RY wire only - 2.5 ohms

• R wire only – 2.5 ohms
• RY wire only– 5.3 ohms before cleaning the rotary coupler connector, 2.6 ohms after cleaning
• Full circuit (both wires), jumpered with a paper clip at the airbag connector – 6.1 ohms before cleaning, 4.2 ohms after cleaning
• Full circuit, with airbag installed – 8.3 ohms before cleaning, 5.5 ohms after cleaning

 

Wow mln01, that is some pretty high level and meticulous diagnostic work, nicely done! DAYUM!!!

 

Good work!
So are you checking the airbag for continuity with a normal ohmmeter? I’ve been paranoid to check mine for fear that the small current induced by the meter could cause the bag to deploy. (I’m an aircraft mechanic by trade and a similar check of fire bottle squibs causes the fire bottle to blow!). I would like to know if this is safe (I have an old but very good Fluke meter).

 

Thank you, Mntnceguy, and thank you, Harvlr. My mantra is diagnose, diagnose, diagnose.

Yep, I used a basic multimeter I got free from Harbor Freight a few years ago when they were given away with any purchase, I recall. I think I ended up getting five of them. I gave one to my son, one to my brother, and I have three. The only problems with them has been that the test leads sometimes come apart, but they can be replaced.

I saw the warning language in the RAVE saying that a multimeter should never be used to diagnose SRS system faults, but I also read and saw other sources online about using a multimeter on an airbag so I went ahead and tried. Plus, I don't think TestBook would have been able to pinpoint the cause of the fault by metering each component of the circuit.

It helped that I have a spare driver airbag module, but I was nonetheless very, very careful the first time I tested the airbag itself. I was outside behind my house. I removed the test leads from the meter before I connected them to the airbag terminal, and then I was careful to be out of the "line of fire" before reconnecting the leads to the meter and then finally turning on the meter. Nothing bad happened, thankfully.

 

Thanks mln. I won’t be as afraid to try it next time.