brake question

mymove

Registered User
My brake light came on and I slowly lost braking capacity until they didn't work at all. I found that when the key was turned on, the hydraulic motor to charge the accumulator didn't run. The fuses all check good. I measured the voltage at the fuse under the dash, and there was no voltage. I fashioned a jumper and powered the fuse from the + side of the battery and VOILA, the pump ran, the brake light went out and I had brakes. My question now is what's upstream of that fuse holding off the voltage? I have the Haynes repair manual, but it appears they don't want to give the reader too much information about the brake electronics. Anyone have a similar problem and know of a fix? Thanks in advance....Bill
 
ABS Pump Relay

Not uncommon for the relay to stick open. It is located up by the firewall under the cowling on the passenger side. Look for the relay with the dark brown plastic case (sometimes called the "brown pump relay"). The GP Sorensen MR-120 is a direct replacement and should be less than 20 bucks at most parts stores. If that isn't the problem, it could be the hydraulic pressure sensor/switch located on the Teves Mark II hydraulic brake unit (AKA master cylinder). Hopefully it is the relay, the pressure switch is pricey and hard to get.

One more thing to check is your ignition switch. All electrical systems are fed through the switch (bad design), and if it goes bad, you will sometimes lose power to the ABS pump. If you can jiggle the key in the switch and get the pump to come on, replace the switch (the rectangular box with the big connector on the column, not the key tumbler).
 
Brake Problem

Larry,

Thanks for your help and insight into my 92SC brake problem. I'm starting to get some idea of how all this stuff interacts. My troubleshooting has uncovered a few more clues, however. I mentioned in my original post that the power TO the ABS fuse was not present. Further testing shows that there is power lacking from adjacent fuses as well: HEGO, turn signals, heater blower, RUN relay, and fog lamps. I recognize that these fuses total about 90A, but I presume the actual loads total much less, explaining how the feed to this fuse group could come from an ignition switch contact? Or is there a power contactor (relay) which is energized from the ignition switch and supplies power to the fuse group? Is it indeed a "fuse group" fed from one source or could all of these functions have gone out coincidentally? I don't think so. BTW, the pressure switch check good. I jumpered the fuse and the pump ran for a while and then stopped all on its own. The BRAKE light went out and I had good pedal.

Any help you could give me would be greatly appreciated. If you don't like typing, you may call me anytime at 269.217.3455 in Kalamazoo, MI.

Thanks again,

Bill
 
There is no power relay between the ignition switch and the fuses.
Most of the fuses that you mentioned (blower, turn signals, HEGO, run, ABS) are powered by the A2 terminal on the ignition switch. The ABS fuse energizes the hydraulic pump motor relay. The ignition switch probably needs to be replaced, as LJGriggs indicated.
 
Back
Top