Recently replaced the ADU on my 91 Vert - had no air bag light on warning cluster.

Now that I've got that fixed, the airbag light blinks 3 times.

Diagnosed that with the workshop manual and found that I'm not getting 12V to one of the two pins, 1J (G/Y) on the gray ADU connector. I've got 12V on the other pin 1L (W/G)...guess I've got an open/short.

Manual says to replace the harness if I'm not getting 12V...

Does this require removal of the dash? I haven't found the schematics showing where the harness is routed and where it connects to 12V supply?

Anybody have any hints or suggestions?

 

Your back up battery is bad or disconnected.

The 1J (G/Y) is the output from the back up battery to the air bag control unit.

The back up battery is just left of the SRS control unit under the drivers dash.

The power for the system, comes from the G/R at the fuse box (30A fuse), then feeds into the back up battery, then coming out of the back up battery is the G/Y.

The plug for the back up battery is a 6 pin plug with only three wires in it (G/Y, G/R, B/R). The Black/Red is ground.

 

To answer your other question, yes, you'd probably have to remove the dash to get the harness out -- because some of it goes up and under the dash.

If for some reason you need some airbag parts (including harness) let me know. I just pull all of that stuff out of my 91 vert. All seemed to be in working order.

 

Mark, thanks.

I completely understand this circuit now and think I've fixed the problem:

Two observations.

1) I made a mistake in not reattaching the backup battery when checking for 12volts on the ADU connector. (Step 4 to Step 5). Did that and discovered a second problem.

2) Once I reconnected the backup battery and tested for voltage, I kept noticing fluctuations 5V to 10V and then a decay...? I pulled the backup battery off of its metal bracket to make things easier to test and discovered that the voltage became constant at 12V (11.95) on the G/Y ADU connector.

The backup battery connector tabs that slip over the metal bracket fingers were broken out (previous owner??) and allowed the battery to sag. I used a tie wrap to hold it in place and must have forced the metal fingers against the exposed solder pads of the battery board, creating a short.

I reassembled the clock connectors (orange and blue) and tested the fixes.

The airbag light behaves as expected now. Goes off after approx 6 seconds.

Thanks again for your help! Saved me some major headaches.