Brake Idiot Light only when turning left (91 Chev Cav Wagon-auto)


What is it about turning left that causes a brake idiot light to come on, then turning to the right turns it off.

It used to happen only on certain railroad tracks on my way home. Now it happens when turning a tight left, even on off ramps from the interstate.

If I drive long enough to turn “enough” to the right, the light will eventually go off.



Well, the most obvious question that everyone wants to know the answer to is:

Have you checked the level of brake fluid in the master cylinder?

And if you did check the master cylinder, did you need to add brake fluid? If you have not yet checked the master cylinder, I would strongly suggest that you not drive the car until you have checked it and, if necessary, filled it to the “full mark”.

After you supply the answers to these questions, then you can expect to get some responses that provide specific advice.


VDC beat me to it.


I am a 53 year old neophyte with cars. This car was bought new and I’ve babied it all this time. I take my cars to my mechanic when they need PM and when there’s trouble. I came here to ask if my issue with the light was a true issue for the brakes or for the light itself. (My father called them idiot lights when I was a child and we’ve always called them this in my family.)

By the way, because I want to know the dynamics at play: Why would turning to the left, but not to the right cause an issue with the master cylinder to cause the “IDIOT” light to come on?


The brake light coming on while driving is nothing to toy with. A car that fails to start can wreck your whole day, but one that fails to stop can ruin (or end) your whole life. Hence the snippy (and admittedly unhelpful) responses.

As far as the light only coming on when you turn left, the fluid in the master cylinder will slosh around as you drive, with the fluid moving to the right as you turn left. Depending on exactly where the “drains” are on the bottom of the master cylinder, turning may cause a pressure drop in left turns if the fluid is low enough. If it were to drop lower, the light would probably come on in right turns also. Some cars have a fluid level sensor in the MC cap, and this could also be affected by turns, but again, only if the fluid level is low (unless the sensor is bad).

Have you experienced any problems with the brakes (low pedal, soft pedal, poor stopping, etc.) other than the light? And what WAS the complete diagnosis?


Sedgy–My point, which I suppose that you did not pick up on, is that this is a potentially serious issue. We all have a responsibility to ourselves and to other people on the roads, and if your brakes failed, you could have been responsible for a very serious accident.

Since you admit to being a neophyte with cars, you should have consulted your mechanic (or at least read the relevant section of your Owner’s Manual) when you first noticed the brake system warning light. If you had chest pains, shortness of breath, and pain in your left arm, but those symptoms later went away, would you wait several weeks to consult with a doctor? This is essentially similar in that it is potentially very serious, and is something that can not be ignored.

So, I did not intend to offend you, but rather to point out that you had a responsibility to follow up quickly with this situation. And, I would suggest that the next time that you see any warning lights on your instrument panel that you stop the car in a safe place, read the Owner’s Manual for the relevant information, and then decide whether you can safely drive to your mechanic or whether it should be towed.


I’ll make another WAG: the problem is the parking brake switch (which will illuminate the same brake light on the dash, in most vehicles, anyway).


NYBo–While I consistently respect your advice, I have to ask you to re-read my first post in this thread. Unhelpful? I think not.

I asked the OP to provide an answer to a very important question, I elaborated a bit, and I asked the OP to post back with a response in order to get some specific suggestions. I was trying to help, even if he/she did not perceive it to be so. And, I don’t think that we ever got a direct answer to the pivotal question that I posed in that first response.


Thanks for the parking brake switch idea, NYBo!

I just remembered (this can happen when you reach 53) that I had a problem when I parked on a hill not long ago and put the pkg brake on. When I started the car, the brake light wouldn't go off, even after taking the pkg brake off. I pulled the brake back on and then off a few times and eventually the light went off. NYBo's thought makes sense (although I'm not going to assume that's the ultimate dx). I'm so sorry that I didn't include that in my original post. I'll be sure to get that checked out, too.

Personal to VDC, I did pick up on the immediacy of brake issues in your post and how important they are to anyone and anything, and agree with you. I also know to pull over when these lights come on, esp check engine light or brake light (believe it or not). However, this instance of the brake light coming on was just such an intermittent thing, with no problems with the brakes (low pedal, soft pedal, poor stopping, etc.), and it was happening only when I went over that one railroad crossing on a curve, and immediately went off when I turned to the right, that it wasn’t “scarey” enough to call a tow truck, as I have when I felt it important enough to do so. (But, it happened again last night as I came back home off the interstate, which prompted my post - my mechanic was closed.) I felt it had more to do with wiring. I have my own copy of a Chilton’s trouble shooting guide for the layperson, and it didn’t reference this problem. Thought I’d come here for some advice before I took time off from work to make it back to the mechanic.

I accept your apology and I apologize, VDC.


I wasn’t referring to your first post, VDC. I see that the “unhelpful” posts have been deleted.


Aha! The parking brake cable may be stretched just enough or the rear brakes far enough out of adjustment to prevent the springs in the mechanism from returning the pedal/handle all the way.


Then don’t drive on the railroad tracks. “But seriously folks,” there is a little float in your brake fluid reservoir that works just like the gas gage. They are famous (Especially in a GM product) for sticking in a low position when the fluid sloshes around in the reservoir. Being very careful, take the reservoir cap off and the little screen (If it is still there) and poke the float with your finger or a screwdriver several times until it slides up and down easily. If that doesn’t work don’t worry about it. You’ll just have to check the brake fluid the old way: by sight.



I would have posted sooner, but it took me a while to find the shop manual for my 93 Caprice. According to the shop manual there three conditions that activate the brake light.

  1. The parking brake is applied, fortunately that seems to be your problem.

  2. During start up to verify the light is working.

  3. The brake differential pressure warning switch monitors the front and rear brake pressure. If it detects a difference in pressure between the front and rear brake systems, it activates the light. Once the light is activated by the switch it will stay on until the system is repaired. Basically, if the light comes on and stays on, there is a real problem with the brakes.

The brake light will not come on if the fluid is low. The Caprice has low warning lights for fuel, coolant, oil and washer fluid. They’re good cars, hang on to yours.

Ed B.


Ed–What you have posted is undoubtedly correct for a '93 Caprice, but are you sure that this is also correct for the OP’s '91 Cavalier?


Thanks VDC,

I need new glasses. I saw “station wagon” and “Ca” and thought “Caprice”. Autozone does have a repair guide for a 91 Cavalier. It looks like the Cavalier has both differential pressure and low fluid switches mounted on the Master Cylinder.

Ed B.


Oh, Beefy Norm… finally a funny man on this post! I’ll take what you’ve shared about driving on the railroad tracks to heart!

This hypothesis definitely has merit. I think I’ll leave the poking around for someone is more confident and I’ll stick to what I do best. I’ll at least offer to hold the worklight!