Technical Tips > Brakes, Suspensions, Steering, Wheels & Tyres
C4 ABS lateral accelerometer - alternate options?
sabre:
--- Quote from: Vettech on May 07, 2018, 08:28:05 PM ---I've got an 87, and I must admit, I've never had a code or any issues.
We are talking the unit screwed to the trans hump just in front of the shifter arent we. Covered in carpet, ac and radios etc etc.
Having typed the above and then going surfing, I now see plenty of people on the web with issues.
Because LA's started back in 84, they were rudimentary devices, now years later they have amplfiers, pizo's etc etc and are micro small.
So being a person who loves to pull things apart and see how they work, I'd love see inside the unit
The basic C4/87 electrical supp book, shows two switches in line, short or open, two wires, whilst other years use three wires.
There is also suggestion of mercury switches being used. The LA appears to be riveted together.
Without getting my hands on one, I find it difficult to understand how mercury switches and or a resister can go faulty.
More likely to have HR connectors or joints esp earths.
Do you have the LA the guy pulled apart !?!?!??......
--- End quote ---
Unlikely to have a code error in an 87. No readable diagnostics in the early units. LA introduced in 93 with LT1. Output is analog signal with max and min at +/- 0,5 g. I believe 95/96 had a different sensor to 93/94.. Definitely not just switches or mercury contacts.
jklumpp:
OK, here's some pics of the inside of the unit.
Looks like a small counterweight on a spring steel pendulum - moves left of right with G loads, within an electrical field which I guess varies the output/resistance... or something
the slight discolouring is on the mounts, not the board - so I'm not sure if that actually means anything or not.
I would need to desolder the joints to remove the board & look at the other side....
Vettech:
Now thats why I have not seen a code, they only go from ~13 thru 53, and yours is different looking (externally) to the one fitted to the 87.
The 87 is clearly designated "Lateral Acceleration Switch" and its basic cct is shown as two (2) series switches (open at 》0.5g's).
Now yours looks like its full of goodies, more goodies equates to more pieces that can fail. Obviously at least three wire connection.
jklumpp:
I forgot to mention - I spoke to Steve @ SR Performance.
...good guy, and very willing to help, but unfortunatly he had no answers for me.... Said he has a customer who was having similar problems, but just decided to live with the ABS light on....
....The search for solutions continues - "The truth is out there"!
jklumpp:
Rediscovered an interesting article I had forgotten I had read a while ago, from the QLD Corvette Club
http://www.qldcorvetteclub.com.au/tech/tech_talk/abs.htm
Most interestingly the author writes:
"The ABS goes through a self diagnostic routine the first time the vehicle passes through 5 kph after turning on the ignition. You have probably heard the pumps operating during this BITE test. (Built In Test Equipment operation) The lateral accelerometer will give a voltage of about 1.2V at 1g right, 4.2V at about 1g left and about 2.6V when the car is running straight ahead. If the control module reads in excess of 0.6g either way for more than 120 seconds, an error is indicated. Either the lateral accelerometer is faulty, or the car is lying on its side"
The readings at 1g would be simple to test - it's just a question of how to measure the voltage.... Anyone have any ideas? Or a wiring diagram that might help?
I have sent an email to the Queensland Corvette Club to see if I can get in contact with the author of the article, and see if he can provide any further advice on the accuracy of the specs he mentions, and how to measure the voltage.
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