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Lateral Accelerometer service

echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
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BaltoWash MD
Corvette
1993 40th Anniversary Coupe
Is the lateral accelerometer in my 93 user serviceable?

I've got an ongoing intermittent error evidenced by Service ABS and Service ASR light illumination that resets to normal when the car is restarted. The CCM tosses an error 76 when this happens. I haven't looked at the unit yet, but am wondering whether to p!an on employing percussive maintenance or just replacing it while I have the console apart?

Thanks,
Jerry

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Robertwav1

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Joined
Jan 7, 2003
Messages
829
Location
Ocala, Florida
Corvette
1993 Blue

Hey Jerry,

Check the brake fluid, every time I went around the corner these lights would illuminate. Found out the brake fluid was a little low? Happened a very long time ago so I'm suprised I remembered. Hope it's your problem.
 

echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
Thanks. I'll do that. It's a long stranding problem and didn't go away the last time I did fluids, but it's worth another shot.

Best,
Jerry

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Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,457
Location
CenCoast CA
Corvette
71 04 12 19
Is the lateral accelerometer in my 93 user serviceable?

I've got an ongoing intermittent error evidenced by Service ABS and Service ASR light illumination that resets to normal when the car is restarted. The CCM tosses an error 76 when this happens. I haven't looked at the unit yet, but am wondering whether to p!an on employing percussive maintenance or just replacing it while I have the console apart?

Thanks,
Jerry

Sent from my SM-T310 using Tapatalk

The lat sensor cannot be serviced. It it fails, you have to replace it.

DTC 76 is, indeed, a lat sensor fault. It sets when the signal from the sensor is out of range for 7.5-min. or more. There are two pages of diagnostic instructions in the FSM for it. The solutions are either to repair wiring and connections, replace the lat sensor or replace the EBTCM. A scan tester with GM chassis software is required to solve that code.
 

echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
The lat sensor cannot be serviced. It it fails, you have to replace it.

DTC 76 is, indeed, a lat sensor fault. It sets when the signal from the sensor is out of range for 7.5-min. or more. There are two pages of diagnostic instructions in the FSM for it. The solutions are either to repair wiring and connections, replace the lat sensor or replace the EBTCM. A scan tester with GM chassis software is required to solve that code.
Thanks Hib. I've ordered the part at this point. I used a the GM cart in a MasterTech to run through the charts in my FSM, but just wanted to make sure. The car is an odd combination of analogue and electronic so I'm never sure whethger or not small parts can be serviced.

Best,
Jerry

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Hib Halverson

Technical Writer for Internet & Print Media
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Messages
13,457
Location
CenCoast CA
Corvette
71 04 12 19
Thanks Hib. I've ordered the part at this point. I used a the GM cart in a MasterTech to run through the charts in my FSM, but just wanted to make sure. The car is an odd combination of analogue and electronic so I'm never sure whethger or not small parts can be serviced.

Best,
Jerry

Sent from my SM-T310 using Tapatalk

If you have a MT with a chassis cartridge or a MSC, you are set as far as diagnostics tools go.

When you say that you ordered the part, you must mean a used sensor as all the ABS lat. sensors for 90-93 and 94-96 have been discon. for a number years. If your diagnosis does lead you to "replace sensor", once you get the new one in place, I'd run the diagnostic a second time just to make sure the sensor you install is operable.

Lastly take note of the FSM's statement about wires/connections problems.

Good luck!
 

echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
If you have a MT with a chassis cartridge or a MSC, you are set as far as diagnostics tools go.

When you say that you ordered the part, you must mean a used sensor as all the ABS lat. sensors for 90-93 and 94-96 have been discon. for a number years. If your diagnosis does lead you to "replace sensor", once you get the new one in place, I'd run the diagnostic a second time just to make sure the sensor you install is operable.

Lastly take note of the FSM's statement about wires/connections problems.

Good luck!
Thanks again, man!

Yes, I ordered a used accelerometer. Thanks for the tip about running the table again. There's a promise that the part won't be DOA but probably not a warranty. They're not exactly common but neither do they appear to be extinct yet.

One thing that maybe you can help me with is the ground location. I haven't had a lot of luck running down ground points in general on this car. I should note that I have one of the white "draft" versions of the FSM, so I may be missing into or looking in the wrong place. I hope to upgrade to the two volume set within the year.

Jerry

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Hib Halverson

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71 04 12 19
There are a number of grounding locations.

Are you looking for the ABS related grounds?
 

echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
There are a number of grounding locations.

Are you looking for the ABS related grounds?
What I'd really like is the knowledge of how to decipher the locations from the FSM! Failing that, small words and pix might work. Seriously though, I think I just haven't found where to look in the book. Or I've run into one of the issues with having the preliminary edition...

Specifically, I have a couple of odd, intermittent, issues (Tach and Ride Control) that could be traced back to a loose or corroded ground. Even the accelerometer issue could be a ground (although in this case, physically tilting the thing seems to indicate that the part needs replaced.)

Best,
Jerry

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Hib Halverson

Technical Writer for Internet & Print Media
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13,457
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71 04 12 19
The white versions of the Service Manuals are preliminary and sometimes incomplete. Do yourself a favor and get the "real" red copies.

Can you be more specific about the tach and SRC issues?

One major ground is a big bolt on the side of the block with a bunch of black wires going to it. It's near the oil filter and that's where the SRC controller grounds. There's another ground on the clutch housing at the left rear of the engine and the PCM grounds to both of those.

The IP grounds to below the left end of the IP on the kick panel next to the driver footwell. You may need to remove trim to find it.

You need to find those locations, remove the fasteners, then clean the fasteners, the surface to which it grounds and the wire connectors. Make sure the bolt on the side of the block above the oil filter is tightened properly.
 
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echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
The white versions of the Service Manuals are preliminary and sometimes incomplete. Do yourself a favor and get the "real" red copies.

Can you be more specific about the tach and SRC issues?

One major ground is a big bolt on the side of the block with a bunch of black wires going to it. It's near the oil filter and that's where the SRC controller grounds. There's another ground on the clutch housing at the left rear of the engine and the PCM grounds to both of those.

The IP grounds to below the left end of the IP on the kick panel next to the driver footwell. You may need to remove trim to find it.

You need to find those locations, remove the fasteners, then clean the fasteners, the surface to which it grounds and the wire connectors. Make sure the bolt on the side of the block above the oil filter is tightened properly.
Truth being stranger than fiction, I lucked out with a bid on eBay last night and scored a red FSM set for less than $50, which is about what I paid for the one I have now. There's no doubt in my mind that it's been worth the money. I knew the white one was a prelim version but at the time I couldn't afford the real McCoy.

The tach problem is intermittent. It had stopped working entirely but started again after I replaced the Engine Coolant Temp Sensor. As part of that process I was moving wires, including the tach filter. It stopped again and I looked a the filter pretty carefully... Which started it working again. I did note that compared to the readout on ALDLdroid, the tach is reading a bit low when working.

I read that the filter can be removed but haven't taken the time to dig up the posts.

As far as the SRC system goes, I have an on-again off-again service light on the DIC. I haven't looked into it at all yet.

Thanks, Hub, for taking the time to work with me.

Best,
Jerry

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echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
There is a lot of information about SRC in this article elsewhere on the CAC.

Get the SRC fault codes and post them.
I'll pull the codes tomorrow. Started on the "76" today as the replacement lateral accelerometer came in. I got as far as taking apart the shifter when I discovered that my snap-ring pliers weren't long enough.

Tomorrow's another day.

Jerry

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echo4golf

Well-known member
Joined
Oct 9, 2017
Messages
55
Location
BaltoWash MD
Corvette
1993 40th Anniversary Coupe
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.

:beer
 
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