My brake light Intermittently goes on and off. Sometimes just a blink and sometimes it stays on for a while and then goes off. Sometimes comes on when they apply pressure to the brakes and sometimes just when I’m driving. Brake fluid looks fine pedal pressure seems good. Any ideas.
MikeGlenny
91 12 cyl xj-s coupe
In beautiful Cleveland
Does the 91 have the brake fluid reservoir like my 88?
If so, very common failure, the cork in the reservoir cap is not floating correctly. Mine did exact same thing. I didn’t want to do the whole Mitsubishi upgrade right now as outlined in The Book, so I simply bought new cap and all is fine. $70 part though…
My XJ has a similar issue. As of now, just no connection at the cap… I just check each Saturday for fluid level, along with the other levels. Dad taught us that. Army style “motor stables”.
MikeGlenny,
When you start up your car after it has sat overnight or for a day or two, do your red BRAKE and amber ANTI-LOCK warning lights illuminate for a few seconds and then.extinguish one by one?
There are a few things that can cause the red BRAKE light to come on and I am wondering if it is a pressure or level sensure issue.
Paul
1 Like
Timeisrelative
(Jason Miller 1993 XJS 4.0 convertible, 1997 XK8 coupe )
9
I was wondering if the pump or accumulator ball could be bad
Jason,
When the accumulator goes bad it seems to cause the amber ANTI-LOCK light to come on. The red BRAKE light comes on with low fluid level in the reservoir, a failure of the low fluid sensor, but also a faiIlure of one of the three pressure sensors in the Combined Pressure Switch. The Combined Pressure Switch in my wife’s 1990 XJ-S convertible went bad and the red BRAKE light came on permanently. I fixed that with a replacement used Combined Pressure Switch and learned a lot about the ABS in the process.
Paul
1 Like
Timeisrelative
(Jason Miller 1993 XJS 4.0 convertible, 1997 XK8 coupe )
11
Ah gotcha! I thought when first starting that both came on until the system built pressure. I’ll have to check mine tonight
Jason,
Yes, after sitting for a while (overnight?) both the red BRAKE light and amber ANTI-LOCK light will should illuminate after starting the car until the ABS pump builds up enough pressure. Then they should go out one by one when there is sufficient pressure in the ABS system. If you never see these lights come on you should suspect a burned out or missing bulb. If the lights work properly and you can hear the pump turn on and off then everything should be OK. I like to test the ABS function from time to time on a strench of quiet sandy back road and firmly push down on the brake pedal at 30 MPH or do until I feel the pulsating vibration in the pedal. The worst time to discover that your ABS is not working properly is when you really need it.
Kirbert-I’d tell you how my ABS pump runs except I have close to zero mechanical aptitude or knowledge and am not really sure of even where it is though I know I have one since I have an ABS indicator that also (though not as often as the brake light) intermittently goes on and off.
Paul. Both lights come on at startup,ABS usually goes off after a few seconds,brake light sometimes goes off in a few seconds sometimes stays on for a random amount of time. Always goes off sooner or later, comes back on randomly. Amechanic tells me it’s a switch/sensor on the pump and can’t be replaced except by replacing the pump. Does this sound right. Car is 91 but before face lift
Any thoughts?
Mikeglenny 91 12 cyl xj-s coupe
Mikeglenny,
Yes, that sounds a lot like what happened to my wife’s 1990 XJ-S convertible except that red BRAKE light came on and wouldn’t go off.
The attached picture shows the Combined Pressure Switch that failed on my wife’s car. I removed and replaced it with one that I purchased on eBay. I believe it might be the same part as in the XJ40. I did not have to replace the pump to do this.
Once I figured out what failed the removal and replacement was pretty straight forward except that I had to find a wrench large enough. I am certain that I posted about this so there should be some info in the archives if you search “combined pressure switch”.
Paul
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
15
You should be able to hear it when you turn on the ignition. It should run about once every half dozen times you apply the brakes. If it runs EVERY time, we’ve found your problem!