End of the season last year, I noticed that the ABS self test was not happening on my car. The test where you hear the pump cycle after you first start the car and exceed 3 or 4 mph. 94 Coupe, LT1 6spd. No ABS light in DIC coming on to indicate an issue. Yesterday, unhooked battery for 20 minutes or so. Today, drive car for first time since noticing this issue last fall. Again, no self test, no ABS light in DIC. (Yes the ABS light does turn on and off when you first turn on the key).

Am at work now, so haven't had a chance to look further. Will check fuse first. I find it odd that it is not turning on the light in the DIC. Would think the computer would see the pump not cycling as being a failure of the test, and turn on the light. Will try to pull codes in the next day or 2.

Also, seems like the pedal moves further than it should, though car still stops fine.

Any thoughts before I can pull the codes?

 

Finally got the chance to look at the car. Checked fuses, all fine. Pulled codes. Only thing I found was a historical for the ASR motor.

The FSM says absolutely nothing about what to do if the car is not performing the self test. Not sure where to go from here. Any suggestions/ideas will be greatly appreciated.

 

Bump

 

Is this something audible? Since I bought my 95 last year I always thought that test was something inaudible. I don't think I've ever heard it. Maybe I'm in the same boat as you.

I'll try again the next sunny day to make sure the stereo is off, maybe it happens but I never hear it because the radio is up loud.

This got me to thinking about whether or not the ABS works. I don't think I've ever locked up my tires but I've not really tried. Does your ABS still work? Again I'll try that out on the next sunny day.

 

Mine has always been audible, as I believe most others have said theirs are. When I first start the car, then exceed 3 or 4mph, either going forward or reverse, I can hear the pump cycle for just a second or 2. The sound comes from right behind the drivers seat, where the ABS pump and components reside. Just a brief 'grrr' noise.

I have not tried to see if the ABS is functional on a road test yet. Guess that would indeed be a good thing to check. I do know that the ASR still functions, lol.

I am just very surprised that the FSM makes no mention of what to do if the self test does not run...

 

Well since posting to this thread I haven't taken the Corvette out but will be tonight so I'll turn off the radio and see if I hear it. I'm also going to road test the ABS and see if it kicks on.

I know this doesn't really help you but thought I'd at least post my results back later tonight or tomorrow in case I don't hear it cycle but the ABS works.

 

Ok thanks for making me aware of a problem I didn't know I had.

The ABS pump does not cycle. I can't hear it if it does. I can also definitely lock up the front wheels as I tried a road test last night. The ASR does function as well although I wish it didn't. lol

I'll take a peek in my FSM manual tonight to see if there's anything in there about it. I'm assuming not since yours doesn't. Mine's a 95 though so it's worth taking a look as yours is a 96. I'll post back.

I do have to say that I'm not going to spend a lot of time trying to fix it. I do know I have incorrect rotors on the front as they're 12" rotors instead of the correct 13". I don't know if that impacts the ABS or not but I'm planning on swapping the correct rotors this weekend or next.

Anyways I'll post back with my findings as I try a few small things here and there but it doesn't overly concern me not having ABS.

 

Ohhhh. So that's what that groaning noise is. My car has done that since I got it 3 years ago. I never knew that it was the ABS pump "cycling". I thought it was a sign that the ABS was on the way out. But, since I had no codes, it was still OK.

Thanks for educating me, "z28cp".

I love this forum.

Mike
'90 'vert

 

Ok so there's nothing in my FSM manual either about what to do with the pump not cycling and no codes being thrown. I'm going to try and take a look at it tonight to ensure there's no loose connections or anything but you'd think that would at the very least throw a code.

Let me know if you find anything.

 

Interesting problem. I just reviewed Service Technology Publication15005.08-2, the training manual for my 90 Corvette's ABS system. I once had a controller go bad and had to replace due to a bad circuit for a wheel speed sensor.

Shooting from the lip:

First of all, it appears your controller is not initiating the BITE (Built In Test Equipment) test. As correctly noted, around 2-4 mph, the pump should cycle. According the STG reference manual "The BITE test cycles each solenoid valve and the pump motor to check component operations." Another sections notes "The EBCM also checks its own logic section and circuitry. If any error is detected during this test, the EBCM will set a code."

Indeed.

Now, your car's ABS system is more advanced than my 90's however, some system operations are similar. What really throws me is the fact you do not get a system deactivation light shortly after you pass 4 mph. From reading my schematic, there is a pump feed (from the controller) to the pump motor relay and a "pump on" input between the pump motor relay and the pump motor feeding a voltage signal back to the control module. These two circuits suggest the command pump on signal and a feedback circuit to the controller to see if there was a voltage change between the pump relay and the pump. Again, this may be slightly different on your model year. Activation of the pump (voltage change I assume) should be noted by the control module, either pass/fail. Should the noted condition indicate "Fail", you should get the system deactivation lights associated with your model year. What gets me is the pump does not self test, AND you get no indication from the control module the system has failed. This leads me to SPECULATE there may be a problem with the control module or power to the control module.

Not sure what your FSM says about brake problems. If you can get access to a Tech 1A or Snap On MT 2500, you can run some pump tests yourself.

As a note, I always thought any hiccup with ABS would result in deactivation of the system and associated warning lights.

As usual, I was wrong.

Not sure if your rotors changed the equation. I'm a little suspicous. Even if the sensors didn't work, the controller should have noted that fact.

Let me know if you have any questions.

dlmeyers