1990 L98 6 sp coupe w/standard suspension and electronic AC

This car had been sitting about 6 years prior to my buying it about 6 months ago. The ABS light has been coming on the whole time but I've been fixing other problems. Now is the time for ABS.

When I first got the car, I took it to a local shop and had them bleed the brakes of the old brake fluid. This seems to have gone well. I still have the ABS light coming on but it stops well.

I opened the compartment behind the driver seat, pulled out the bin and the sound insulation to look at (and hear) the ABS pump.

Ignition on, I get the ABS light briefly then it goes out. Upon start, light out. Start to roll and the ABS light came on. No pump cycle.

I pulled out the two relays on the pump and "tapped" them a bit and re-installed them. Now I get the pump cycling correctly when I start to move....then the ABS light comes on after couple of blocks of driving.

As a test, too her out to a paved country road and killed the motor. Upon restart, I got the brief ABS light, OK. I started to move and I got the growl of the ABS pump check, OK. I quickly punched her up to 40 mph and put the right tire in the gravel shoulder that the left on the pavement and punched the brakes. The ABS pump properly growled and the car tracked straight as it stopped--system OK. I could do this 3 times in quick succession before the ABS light would come on and no more ABS.

What could cause a fault that would shut down ABS after a couple of blocks of driving?

Thanks!

 

My '90 is having the exact same issue. I haven't touched my abs pump, but cleaned all my sensors when I recently did my brakes. I hear the abs pump cycle after starting. I had read in some threads a dirty sensor is common for the abs light. I bought a FSM a week ago and have not had time to look more into it yet. I Also haven't checked for codes on the system yet. So I will be learning as you learn on this one, and if I can contribute to help you I will.

 

I pulled out the two relays on the pump and "tapped" them a bit and re-installed them. Now I get the pump cycling correctly when I start to move....then the ABS light comes on after couple of blocks of driving.

If the ABS did not work until you "tapped" these relays, perhaps they are failing after driving some distance?

 

It's been my experience that if the pump passes the initialization then the problem is in one of the wheel sensors. Mine still works (knock on wood) but when I was replacing the soft lines this winter I saw that one of my four abs sensor wire insulators was disintegrating. I black electrical taped it up and so far it is functioning properly.

 

RexS. I checked my aldl code for the abs tonight (a & h on the aldl plug) and it came up 76 - lateral accelerometer. FSM shows to check voltage on it to see if it is bad, I guess it is under the stereo in the center tunnel. I won't be able to work on it until next weekend. If you check your aldl and it is a different code I will check it in my FSM, maybe it is the same code since our systems are acting the same.

 

Hmm, interesting thought. I just got back from a SuperBowl party...what a rout! I won't be able to check my 90 until late in the week. I have noticed that it seems like the ABS light comes on when I turn the car. I assumed it might be something about the difference in the wheelspeed but I hadn't considered the lateral accelerometer. I'll check my codes later this week. I wonder if the accelerometers are still available?

 

Didn't read thread, but I bet you have dirty abs sensors. IE rusty/corroded especially after sitting for 6 whopping years.

 

Pull the codes and it will tell u what señor is bad. If it's a sensor. Mine would come on about ten mins into a drive. Had to replace the passager rear. With a used one that I found on here. They don't sell theses new anymore for a 90

 

I did a quick search and I only see used lateral accelerometers on ebay or salvage sites. I see Rock Auto has a right rear wheel sensor new, so if your code comes back right rear you will be in luck for that one,

If it is coming on at turns it may make sense for the lateral accelerometer, my light comes on after a minute or so no matter what.

 

Tonight I went out and shorted A to H and I got (3) 12s as expected then I got three 76s and then (3) 12s. Code 76 is "lateral accelerometer signal out of range (1of 2)"!

I've got to remove the Bose system on this old girl so that will give me access to the accelerometer. Maybe it will just be a bad connection.....yeah, sure.

I had already cleaned the wheel sensors so the only thing really left was bad wiring and that can be a beast to chase down.

I had to try 4 times to clear the codes but I got it done. Some of the postings I have read say that just clearing the codes sometimes can have a major effect on the system.

I'm going to be driving my 90 over the weekend from Phoenix to Tombstone so I'll get some miles on her. The more I drive, the healthier she gets.

thanks

 

OK, maybe "eureka" is over the top but I bought a used lateral accelerometer and installed it in place of the existing one under the radio. A bit of a pain getting off all the console plastic but the new part is a direct fit. Two screws and a junction plug.

I fired up the old girl and everything cycles properly and the ABS light now stays out.

Next, cruise control....

Thanks, everybody!