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Chrysler Repair/Brake/ABS lights 'on', '91 Imperial


QUESTION: I have a 1991 Chrysler Imperial with  84000 miles 3.3L engine. The ABS and Brake lights illuminate momentarily anytime the brake pedal is firmly depressed. If pedal is slowly depressed lights stay off. The vehicle stops ok but not sure if it stops as it should as I have nothing to compare it too. It stops better than my 67 Camaro but not nearly as good as the 2013 Explorer.

I have taken it to the Chrysler dealer and below is a narrative between the dealer and a Chrysler agent.

Dealer Input: There are no codes, pump runs and shuts off brakes feel good thought I would quiz you first did recall test ( recall 685) all passed no manual to diag.

Agent Response: Are there any codes? Do Brakes work or just the warning lamps on? There are a lot of parts that are only covered for a certain time period, per the campaign. So you will have to make a determination from there. Report back.

Dealer response: no codes warning lights only come on for 2 seconds with pedal input

Agent Response: Per your findings I found no related cases on this concern at this time. I could suggest following the service manual information. Report any findings.

Dealer response: redid test for piston and pump recall for Bendix 10 pressures past the test never went under 200# in 120 seconds no codes we don't have a manual for this.

Agent response: I assume the vehicle has returned. What assistance is still needed? Have any parts been replaced?

Dealer response: no parts have been replaced no codes amber and red brake light come on when I hit the brakes have done the test for the recall pump and hcu test good I don't have a manual to go any further.

So as you can see nothing has been done to fix the problem. Do you have any suggestions as to what the problem might be?

I have had suggestions it may be the ABS module or the Accumulator. Your thoughts??

Thanks in advance for your help

I do have the '91 manual which does cover the Bendix 10 ABS system. But I don't have any additional manuals about special issues or recalls. It is a complex system.
As regards the exchange between the dealership and the agent, there is one possibility to consider: did the technician who was testing the abs module to find whether any fault codes were present use the correct diagnostic data link connector to connect to? It appears in my reading of the wiring diagrams that there are actually three different places to plug in the Chrysler Diagnostic Readout Box II: in the engine compartment (a black plug for engine codes only), under the dash on the left hand end (the body computer plug which is blue), and under the dash just to the left of the steering column on the vertical support (the ABS plug, which is identical to the body computer plug). If I am correct and there are two identical plugs, did he actually seek codes from the ABS plug? You could ask at the dealer for an answer about that. The blue plugs (called the 'data link connectors' have 6 pins) and if there are two of them then one would have 4 wires and the other have 2 wires; if there is only one such plug it would have 6 wires. The 2 wire plug would be the one for the ABS code readout.
The two questions I have is whether both the lights come "on" when the pedal is pressed firmly and the vehicle is at rest, and do the lights behave exactly the same when the vehicle is in motion and you press equally firmly? Second question: do the lights stay 'on' for the same duration of time under those two conditions as well and for how long (or do they only go off when you release the pedal)?
Absent an indication of mal-braking my first thought would be either a low brake fluid level in the reservoir (or a low fluid warning switch which is too conservatively 'set') or an off-balance of pressure in the overall hydraulic system due to a slight leak at one of the wheel hydraulic cylinders. Do you loose any brake fluid over time such as to have to add fluid, or do you see any signs of brake fluid on the inner sidewalls of the tires?
Please read the PS below, and respond.

---------- FOLLOW-UP ----------

Thank you for your answer. The answers to your questions are below.
The technician states he used the blue plug located under the dash on the left end and has 6 wires.
Yes, both lights come "on" when the pedal is pressed firmly and the vehicle is at rest and no the lights behave a little differently, they appear to stay on a slight bit longer when the vehicle is in motion and pedal is pressed firmly. Second question: no the lights stay on a little longer when in motion. When at rest both lights on for approximately one second and when in motion approximately two seconds then go out when pump stops running.
Brake fluid level is good and there are no leaks noted at any of the wheel brake cylinders. and have not noted any fluid loss the past year.
Your last statement in your answer said ,"please read the PS below, and respond" There was no PS.
Thanks for your time and help in this matter.

I still wonder if there might not be a separate diagnostic readout socket for abs system. May I suggest that you look under the dash to find the blue socket at the left end of the dash and when you find it see if it has 6 wires (one for each of the pins). If so then that means the diagnostic readout would have accessed the abs control module for a fault code and there is none, apparently. On the other hand if you find that it only has 4 wires then there is that second socket by the steering column which is where the reader has to be inserted to get any abs fault codes.
Otherwise, without a code and no other clues I too am at a loss as to what the lights signify.
In re the PS, it should ask you to click on the tab below to thank/rate me and once there you will be given an opportunity to give me a nomination for 'volunteer of the month, which I would appreciate.

---------- FOLLOW-UP ----------

Thanks for your quick response. I did check the Blue socket and it does have six wires.
In your opinion is there a possibility the accumulator could be the culprit or the ABS module?
Thanks for your time and help

No, as I said earlier if there is indeed no code then I would not replace any major parts in the hopes that solves the warning light issue. Only a code should be in hand before replacing expensive parts.
I mentioned a slight in-balance between the two branches of the system as a possible cause for the warning lights. That is the classic cause. It could be a leak, but now I have a second idea to consider: that one of the rubber brake hoses that attach between the wheel brake cylinder and the body brake line at each of the 4 wheels has degraded over all these years such that the lumen of one of those rubber hoses has fragments that are impeding the flow of brake fluid to the wheel cylinder. That would manifest itself as a dragging brake, so touch each of the 4 wheel after driving for a while at road speed and coasting to a stop to see if one of the wheels feels warmer than the others (of course step on the brakes firmly to begin the road test so as to set up a drag situation if it is present>. Let me know if you find something like that. It would be about the time to have those hoses getting flakey.
Thanks for doing a rating and nomination again for this answer should you care to.

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Roland Finston


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