Mechanics

GRAND ABS BRAKE ISSUE

1994 Plymouth Voyager • 6 cylinder FWD Automatic • 78,585 miles

I have a 1994 Plymouth grand voyager and my AMBER ABS light has come on while having strange braking issues. On normal braking the pedal goes down with effort then nearing the total stop it gives out a bit and looses brake power cause the need to push harder. Duplicating the same issue (out of traffic) I hear a buzz noise driver side in the engine area. Reasearch told me that it may be the ABS pump - ABS relay- or can it be the control box. Can you help narrow the issue. I am very handy with Cars I just hate to buy the wrong parts that are not needed. Could a bad relay do this? (Looking towards the lowest repair value first : -)

Ron
Avatar
Eclipset
November 25, 2010.



Once the light has turned on, there will be at least one diagnostic fault code stored in the ABS Computer. That will lead you to the circuit or system with the problem, not necessarily the specific defective part. The buzzing you're hearing is the computer activating the solenoids to modulate brake fluid pressure to one or more wheels in response to the computer thinking one wheel is slowing down too fast. That can be due to a loss of signal from one wheel speed sensor for a number of reasons. When the yellow warning light turns on is a clue too. If it comes on while driving and not pressing the brake pedal, the computer might be detecting an extra pulse from one front wheel speed sensor per tire revolution due to a cracked tone ring. That's what's happening on my '95 Grand Caravan. It takes from 100 feet to a mile or more before the light turns on, and it will reset off each time the engine is restarted. If your light turns on before the van is moving, there is more likely a problem in the hydraulic controller or pump. The system is deactivated when the light is on.

I also have a '93 Dynasty with the Bendix-10 system. That one gets its power assist from the pressurized brake fluid that is held in storage. If you have that system, a pump problem will have an affect on your power assist. There was a recall on that system to replace the piston assembly in the master cylinder. My '95 ABS system is different. That uses a standard vacuum power assist booster so it will still have normal power assist if the ABS system shuts down. I'm not sure which system was used in '94.

Start by finding a mechanic with a scanner that can access the ABS computer to read the fault code(s).

Caradiodoc

Caradiodoc
Nov 25, 2010.
Previous when fist getting the vehicle, I tried to force ABS to kick in. I really stopped fast and the van did slide so I assumed the ABS did not work as it should or atleast doesn't work as good as newer systems. I have (6 months ago) replaced the drive shafts and inspected the sensors (front) and they were fine (cleaned and re-installed).

At first, Amber light turned on only after the pedal drop was happening. To explain the pedal drop better - When doing a normal slow to say a stop sign - the van would slow normally and most judge distance and start to apply more pedal pressure knowing we will not stop at the intended target - just before reaching the intended target the pedal drops about 1 1/2 inches and loss of brake grab is felt and that is when the buzz happens followed by yellow light at that point. As reference to above is that how the acutal ABS system works as intended? As mentioned I tried to make it work as intended when it was first bought. Now the ABS amber light is light when the engine is started but not after every start. And the issue explained with pedal drop doesn't happen at every stop target and doesn't happen in turns or other mild braking situations.

May try this: http://www.amazon.com/Roadi-RDT45-Diagnostic-Trouble-Transmission/dp/B002HSX7P8 - since it does ABS systems too.

I have a 350z turbo - and since I did all the work myself I can probably figure this out with time. I just don't know the mechanics of an ABS system that old. :-) Mechanics charge an arm and a leg these days.

Regards!

Tiny
Eclipset
Nov 25, 2010.
I found my '94 service manual. It would appear you have the Bendix-4 ABS system. That uses a standard master cylinder and vacuum power booster.

I really get the impression there is internal leakage taking place in the master cylinder based on the pedal dropping but it would seem the red warning light would be on too for unequal pressures in the two hydraulic circuits. It is also possible for there to be a leak in modulator but I don't have any experience working on them. I DO know you don't want to let the system run out of fluid while replacing other brake parts such as calipers and wheel cylinders. The base brake system can be pedal-bled with a helper, but you must have the Chrysler DRB2 or DRB3 scanner to activate some valves to bleed the modulator.

There are no fault code descriptions shown in the service manual but they do make reference to latching and non-latching codes. Latching codes deactivate the system even if the problem is intermittent and goes away. You must turn the ignition switch off and restart the engine to reset the system. With non-latching codes, if the problem goes away, the light will turn off and the system will be functional again without having to cycle the ignition switch off and back on. Either way, the fault codes will remain in the computer's memory. Having those codes read will point you toward the cause of the problem. If an intermittent problem doesn't show up for a long time, the codes will erase automatically after 50 engine starts so it's important to have them read before that happens and that valuable information is lost.

Caradiodoc

Caradiodoc
Nov 26, 2010.