The DLC76 seems to be fixed. (Long Post Warning!)
"Man, these cars are a weird mixture or electric and electronic technologies"
Issue: Service ABS and Service ASR lights illuminating regularly.Initially pulling the codes showed a 72 (history) and 76 (current) set. On clearing the codes, a test drive saw only the 76 reset. This was not a surprise as the issue has been around since I got the car.
Troubleshoot DTC 76 (Lateral accelerometer out of range.)
The lateral accelerometer measures yaw rate (lateral g force) in cornering and feeds the data into the ASR system. DTC 76 sets when the lateral accelerometer data departs from an accepted range for more than 7.5 minutes. When 76 is set, the ABS and ASR systems shut down and will not function until the code is cleared. Non-antilock breaking (i.e. old school Chevy power brakes) is still operational).
The lateral accelerometer uses a Hall effect sensor (
Hall effect sensor - Wikipedia) that measures yaw rate as deviation from a voltage which represents 0 G (about 2.5 volts). Turning to the left pitches the LA to the right and causes the voltage to drop. Turning to the right causes the LA to pitch to the left and the voltage to increase. The harder the turn, the more deviation. These deviation is translated to g-force for the ASR system to interpret. (Note: Bosch literature indicates that later model sensors can differentiate between normal yaw rates and breaking the rear end of the car loose but I'm not clear that the ASR works that way. I think it works by measuring wheel speed...)
Armed with this knowledge and the FSM chart, troubleshooting was straightforward.
Step 1. Monitor the LA output voltage. I think that you can do this from the console on the 93, but I used a MasterTech 3100 with the GM Chassis cartridge.
Switch Off and connect the MT.
Switch On:
Turn on the MT
Load the Tech 1 cartridge. (F0)
Access the Chassis app. (F1)
Enter the year, type, and fourth letter from the VIN at the prompts
Select ABS ASR
Select Data
Right Arrow until the LA voltage appears. (You can also hit RCV for an extended data list but it is limited to the G readings.)
Since the engine is not running and you're not turning, the voltage should be 2.55-2.85 (indicating 0 G)
Problem 1: My car was reading 1.33
Step 2. Disassemble enough of the center console to access the LA. It's under the radio.
Switch off.
Disconnect the ground at the battery. (Don't ignore this! You'll be pulling the Cigar Lighter and it's got power even with the key off.)
Set the parking brake as you'll want to be able to put the shifter in different positions. Mine's an automatic but the FSM pix for a manual look similar.
Remove the shifter button by carefully prying it up. I started in the back and then worked my way around until it popped free.
Remove the shifter knob
Pull the snap ring inside the knob. It takes a fairly long set of snap ring pliers to do this.
Work the knob free. I put a bit of WD40 in to act as a penetrating oil and the knob came free.
Remove the Console Trim Plate
Remove three screws, one under the rubber drink holder, and two under the carpet in the Center Console Compartment.
Slide the Trim Plate back and then disconnect the lighter, automatic shifter light, and the accessory plug harness.
Remove the Center HVAC difussor by pulling two Torx head screws, one on either side.
Expose the LA by removing the Accessory Trim Plate.
Pull one bolt on top (under where the diffusor was) and two from the bottom.
The FSM says to pull the Radio Control, but I didn't have to.
Remove the two bolts holding the LA in place.
Step 3
Reconnect the battery.
MT reconnected
Switch on.
Roll the LA to the right 90 degrees. (Right side down.)
Check voltage. Should be 1.05 - 1.35v.
Here's where it went wrong for me. The reading was correct. And when I checked the voltage with the unit straight up it was functioning as advertised.
Step 4.
Roll the LA 180 degrees to the left. (Left side down.)
Check voltage. Should be 3.5.
It's right. Again. At this point the LA appears to be fully functional. I swapped the new-to-me one in and it functioned identically.
Step 5. Carefully inspect the wiring and look for intermittant issues as I "wiggle test" each wire. No dice.
At this point it was too dark to work so I put stuff away for the night and picked up with step 6 the next day.
Step 6. Test drive and see if the code re-sets.
I did and it did. Not only that, the LA showed 1.1 volts again, sitting still, rather the 2.55-2.85 range. Further, when I moved it around, the reading did not change.
Bingo! I replaced the LA.
My son and I "test-drove" about 20 miles of nice, twisty roads.
DIC remained silent (except for the Sevice SRS light-- but that's for some other time.)
Tomorrow, I'll put things back together. I'll keep an eye on it, but right now it looks solved.
My thanks to @Hib Halverson, @RobertWav1, and the other folks who chimed in on this issue.
