Eagle Posted April 27, 2008 Share Posted April 27, 2008 BRAKES ARE A WONDERFUL THING! My brother came over and we bled the MJ, and it now has good peddle and 4-wheel brakes. It hasn't stopped this well for at least a couple of years. But ... ... I now have a constant brake system warning light. I thought the light was supposed to reset automatically when you fixed whatever problem there might have been, and bled the brakes. I've bled the brakes on the MJ before, and lost the rear brakes on the XJ and repaired and rebled, and I've never before encountered a stuck brake warning light. Anyone have any good ideas how to get it to reset? Link to comment Share on other sites More sharing options...
jtdesigns Posted April 27, 2008 Share Posted April 27, 2008 what all will cause the light in the first place?? low pressure?? low fluid? Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 27, 2008 Share Posted April 27, 2008 Possible brake warning light causes: 1. parking brakes are applied 2. very low pedal 3. low fluid level 4. excessively worn brake lining 5. there's a pressure differential between the front/rear hydralic systems But I'm sure you know this. :D If everything is okay, I'd just swap out the pressure sensor at the combo valve. Link to comment Share on other sites More sharing options...
CWLONGSHOT Posted April 27, 2008 Share Posted April 27, 2008 I'll bet the lil do-hickie in the "proportioning valve" is kaputz. When I did my rear brakes it stayed on on me also. Swapped it out and no more issues!! CW Link to comment Share on other sites More sharing options...
Pete M Posted April 27, 2008 Share Posted April 27, 2008 You wouldn't be the first to accidentally nudge the parking brake pedal juuuust enough to turn on the light. :D Link to comment Share on other sites More sharing options...
Eagle Posted April 27, 2008 Author Share Posted April 27, 2008 The light came on because I lost the rear brakes. That part is no mystery, and it did what it is supposed to do. The mystery is why it doesn't reset now that I replaced all the lines and bled the brakes. It isn't the parking brake peddle -- I still have to replace a siezed cable, so I am exceedingly careful not to apply the peddle. I'm hoping if I crack a front bleeder and stomp on the peddle it may move the shuttle valve the other way. Can't think of anything else to try. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 28, 2008 Share Posted April 28, 2008 The light came on because I lost the rear brakes. That part is no mystery, and it did what it is supposed to do. The mystery is why it doesn't reset now that I replaced all the lines and bled the brakes. It isn't the parking brake peddle -- I still have to replace a siezed cable, so I am exceedingly careful not to apply the peddle. I'm hoping if I crack a front bleeder and stomp on the peddle it may move the shuttle valve the other way. Can't think of anything else to try. On my 91 w. a malfunction closes the pressure switch and applies a ground to turn on brake light. Does the brake light go out when you disconnect the wire from the switch? I'm still bettin' the switch is stuck closed. Link to comment Share on other sites More sharing options...
BLHTAZ Posted April 28, 2008 Share Posted April 28, 2008 Does the brake light go out when you disconnect the wire from the switch? I'm still bettin' the switch is stuck closed. That is exactly what I was going to ask/say. Link to comment Share on other sites More sharing options...
james750 Posted April 28, 2008 Share Posted April 28, 2008 don't your need to either unplug the battery for a few minutes or 51 key-on cycles to reset the warning lights. I know this is true for the chk engine, but not sure about the brake warning Link to comment Share on other sites More sharing options...
Eagle Posted April 28, 2008 Author Share Posted April 28, 2008 don't your need to either unplug the battery for a few minutes or 51 key-on cycles to reset the warning lights. I know this is true for the chk engine, but not sure about the brake warning There is no check engine light on an '88 MJ, and the Renix ECU doesn't store codes. The brake warning light has nothing to do with the ECU, it is controlled directly by the plunger switch on the metering block. Your '90 is the same. Link to comment Share on other sites More sharing options...
james750 Posted April 29, 2008 Share Posted April 29, 2008 Thanx for the info Eagle. What year did they start using the Check engine light? I know that my old 92'xj had it... I am just realizing now that i learn more and more everyday on these forums.ive learned more about the mj in the past few months than i ever new b4. Link to comment Share on other sites More sharing options...
Eagle Posted April 29, 2008 Author Share Posted April 29, 2008 Thanx for the info Eagle.What year did they start using the Check engine light? I know that my old 92'xj had it... 1991 was the first year for the Chrysler electronics and the OBD-1 on-board diagnostics. I'm still not sure the brake warning circuit goes through the ECU, though. The switch is exactly the same as it is on the Renix models. Why would they route it through the ECU? I thought OBD-1 only monitored engine functions, not chassis functions. Link to comment Share on other sites More sharing options...
mjeff87 Posted April 29, 2008 Share Posted April 29, 2008 you need to press the pedal hard (very hard) from inside the cab until you hear a "pop" sound from the prop valve. That resets the switch. Jeff Link to comment Share on other sites More sharing options...
watchamakalit Posted April 29, 2008 Share Posted April 29, 2008 you need to press the pedal hard (very hard) from inside the cab until you hear a "pop" sound from the prop valve. That resets the switch. Jeff I was just about to say that. I had a 91 XJ that I couldn't get the light to reset in and I finally read the manual :roll: and it said to apply lots of pressure to the pedal to reset the switch. One quick stomp later all was well. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 30, 2008 Share Posted April 30, 2008 you need to press the pedal hard (very hard) from inside the cab until you hear a "pop" sound from the prop valve. That resets the switch. Jeff I was just about to say that. I had a 91 XJ that I couldn't get the light to reset in and I finally read the manual :roll: and it said to apply lots of pressure to the pedal to reset the switch. One quick stomp later all was well. I've been through my manual and never saw that. Did you see it in the FSM? Just wondering how this worked out for Eagle. Also am curious what caused the switch to pop out it in the first place. I've replaced basically everything on my brakes (booster, master, rear drums, most lines) and never had this happen. :dunno: Link to comment Share on other sites More sharing options...
mvusse Posted April 30, 2008 Share Posted April 30, 2008 My brake light is never on. Then again, I think the bulb is bad. :D Link to comment Share on other sites More sharing options...
Wildman Posted April 30, 2008 Share Posted April 30, 2008 you need to press the pedal hard (very hard) from inside the cab until you hear a "pop" sound from the prop valve. That resets the switch. Jeff I remember seeing that in the Haney's manual, it need something like 250 pounds of pressure to "reset" the switch. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 30, 2008 Share Posted April 30, 2008 My brake light is never on. Then again, I think the bulb is bad. :D Doesn't it come on when you use the e-brake? Link to comment Share on other sites More sharing options...
mvusse Posted April 30, 2008 Share Posted April 30, 2008 E brake? What's that? The front cable is missing, both rear cables have rusted through, the equalizer and spring are missing. I never did try to push the pedal down, though. Isn't the light supposed to come on when you first turn the key on as a test? I will fix the parking brake at some point in time, but with an automatic transmission it's not that big a deal. I have more important issues to fix right now. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 30, 2008 Share Posted April 30, 2008 E brake? What's that? The front cable is missing, both rear cables have rusted through, the equalizer and spring are missing. I never did try to push the pedal down, though. Isn't the light supposed to come on when you first turn the key on as a test? I will fix the parking brake at some point in time, but with an automatic transmission it's not that big a deal. I have more important issues to fix right now. lol - understand. The brake light is supposed to come on when cranking, the light goes out after the engine starts; a self test. Unless the pressure switch is stuck. :D Link to comment Share on other sites More sharing options...
jtdesigns Posted April 30, 2008 Share Posted April 30, 2008 I know my Honda has a lil float on the lid that tells you fluids low, but I know mj's don't.. Do the newer xj's have a low fluid sensor?? (double boost swap*) Link to comment Share on other sites More sharing options...
mjstiltheydie Posted April 30, 2008 Share Posted April 30, 2008 Eagle I had simular situation with my 88. After changing out the rear cylinder and bleeding the system the brake light would not go off. It stayed on for over a year. Until one day someone pulled out in front of me and hit their brakes. At the time I had not upgraded my master cylinder and booster yet. I stood on that brake pedal like I never did before, including driving an old beat up 51 chevy pickup and have deer jump out in front of me. Anyway, after that the light went out. I am not sure what made it go out, if something reset itself or an air bubble was forced out or what, but it worked. For what is worth, try stepping hard on the brake and I mean hard - test those seat bolts. What can you lose. PS Don't do it in traffic like I did, especially if your brakes will lock the tires. I would try it at a stand still. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 30, 2008 Share Posted April 30, 2008 I know my Honda has a lil float on the lid that tells you fluids low, but I know mj's don't.. Do the newer xj's have a low fluid sensor?? (double boost swap*) Naw, the wife's ex-01 XJ didn't have it. But the late 80s Wagoneers that had the rare Sentinentel system monitored all the fluids. But they were leaky bastids........ :D Link to comment Share on other sites More sharing options...
Eagle Posted April 30, 2008 Author Share Posted April 30, 2008 For what is worth, try stepping hard on the brake and I mean hard - test those seat bolts. What can you lose. Well, the reality is that what I could lose is the rusty section of hard line from the rear hose "banjo" fitting to the left rear wheel. However, I suppose it would be better to lose that in the driveway than when a deer (or child) darts out in front of me. Link to comment Share on other sites More sharing options...
Biotex Posted November 12, 2013 Share Posted November 12, 2013 Bringing this thread back from the dead because I've been driving with my brake light on ever since I swapped in the 8.8 rear end. All this time, all I had to do is press hard on the pedal... :doh: Hope I can save someone else from such embarrassment. Link to comment Share on other sites More sharing options...
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