2000 LS3 - Service Light and Brake light on

[birdbarian]

I was googling and found this site. Very informative. I've read through all the threads I could find here on the Brake light and Service lights being on at the same time, and the prevailing opinion is that there is a problem with the brakes.

Here's my story. Driving down the road and both lights come on. Stop by the auto parts store and have them use their OBD. It doesn't show any codes. Bring it by Kauffman Tire to have the brakes checked out, and they say everything is fine and dandy. The service guy did say they topped off the fluids. The tech said they don't do electrical work, but it is most likely 1 of 2 sensors. The e-brake sensor or the master cylinder sensor. I'm guessing that it isn't the e-brake sensor since I don't get the alarm bell when I drive with the light on. I'm guessing it is the m/c sensor. I haven't been able to figure out where that thing is located, or what is involved in switching it out.

I'm wondering if I should take it to another shop and have them look at the brakes, or just try swapping out the sensor.

I'm an IT nerd, so I know how to troubleshoot, just don't know much more than the basics about autos.

[birdbarian]

I suppose its actually an LS2... either that or I have the only LS3. Guess i was thinking about the 3 Liter engine.

[fdryer]

The brake light indicator is about low fluid in the brake master cylinder and activating DRL's. Is it the engine or wrench light that's on? The service engine light relates to emissions issues while the wrench light relates to burned out bulbs and other miscellaneous issues.

[birdbarian]

Thanks a lot for your reply.

It is the wrench light, and it says service next to it.

Does it make sense that both would be on together? Is it possible that the sensor was dislodged or disconnected? I had dropped my son off at cub scouts, and the drop off location required that I drive down a dirt road. I noticed the lights on not long after that.

Can you tell me where the sensor is, and I'll take a look and make sure it is still connected?

ETA: what is a DRL?

[fdryer]

Service Wrench (5) means miscellaneous items. Service Engine Soon (4) means emissions related issues. The reason a reader cannot display wrench codes is because generic readers aren't required to except better ($$) readers. SES indicators can be read by most readers. GM and every other dealer will have expensive readers/scanners to read any error code and charge for it. Personal readers come in every price range to match requirements of the owner.

The brake level sensor is on the brake master cylinder with a two-wire connector. Is the fluid at level or below? If below, the brakes may need servicing. When were brakes serviced last (new brake pads, rotors, etc.)? If not needing service then when were the brakes inspected for possible fluid leaking? Fluid level sensors and wiring aren't prone to breaking. If fluid is level is low then the brakes are worn.

DRL - daytime running lights, a GM company safety promotion to use lighting in front for better presence in traffic (head lights or parking lights).

[birdbarian]

I called the company where I usually get my car repaired, and asked if they have the OBD that reads GM codes. They do and said they want $125 to read the error code, but don't charge the fee if they do the repair work

Fluid level in the reservoir was well above the Minimum line. I took my car to a tire/brake place I've used for years and had them check the brakes. They said the brakes were fine. I had my other mechanic rotate/balance the tires a few weeks ago, and they checked the brakes too. Brakes checked twice in the past month or so, and I only drive ~ 50 miles/week.

I'm hoping it is just the sensor, and not something with the master cylinder.

I figured if it was the emergency brake sensor, then the warning bell would be dinging like crazy.

Any idea what is involved and approx cost of replacing the m/c sensor?

Thanks for your responses and willingness to share your knowledge.

[fdryer]

From the service manual;

A brake fluid level switch, located in the brake fluid reservoir (attached to the master cylinder), is also provided. The switch will activate the RED BRAKE telltale lamp (located on instrument panel) should the brake fluid level become low. After the brake fluid level is corrected and a moderately high brake pedal force is applied, the RED BRAKE telltale lamp should go Off.

Remove the low brake fluid switch electrical connector and remove the switch by depressing the tabs on the opposite end of the switch.

I would seek a shop to check whether this is the brake fluid level sensor or brake switch fault. I don't know prices but you can check with places like Autozone or rockauto.com.

[birdbarian]

Thanks a lot, I really appreciate it. I'm planning to bring it to the shop next week.

[birdbarian]

My mechanic says it is the fluid level sensor, but he can't get the part. Says the only way he can get it is if buys the kit to replace the master cylinder.

Does this look like the right part? I was going to post a link, but I'm a noob so it won't let me. If you go to autozone.com and put in SU1319, should come up with a description of
Duralast/Sensor - Brake Fluid Level
Click to View Details
Part Number: SU131

[fdryer]

Yes, that's the part.

According to the wiring diagram, disconnecting this sensor, if the switch is broken in the closed position and the e-brake is released, the brake light should be off. If fluid level is low then the switch would close and connect a low voltage reference to ground to inform the bcm that brake fluid is low and turn on the brake light. If you have a multimeter you can measure the sensor on/off resistance to see if the sensor failed. Its just a simple on/off switch that senses fluid. The main wiring harness can be shorted to test the indicator too.

Does this car have ABS?

[birdbarian]

It does not have ABS.

I do have a multimeter. I'd just need to know where to test.

[fdryer]

Without ABS all basic brake systems have power assist using the vacuum boost unit behind the brake master cylinder. In addition to this, there's rear brake proportioning valve that reduces hydraulic pressures applied to the rear brakes to prevent rear wheel lock up from weight shift. This brake proportioning valve has a switch that detects hard braking and turns on the brake light. Turning the brake light off requires the car in parked position and pressing the brake pedal firmly to reset the proportioning valve switch to turn off the light. Try it.

Tap the side of the brake fluid container several times with a screwdriver handle. This may free a stuck magnetic float inside the fluid container. A stuck float sensor would suggest old brake fluid.

If these suggestions doesn't work then read the resistance of the removed brake sensor switch. The service manual does not mention anything about draining the master cylinder so tread lightly here. As a sensor, all it does is detect fluid level via a floating magnet within the master cylinder and either switches ON or OFF. A resistance check for each state may require a small magnet; a sealed reed switch operates in proximity of a magnet - when the magnet is close by the reed switch closes a set of contacts and when the magnet is further away the switch opens. http://www.meder.com/fileadmin/meder...pplication.pdf

[birdbarian]

Thanks for all your help. I'll go brave the heat and try your suggestions. I worked on magnetic tape units in the Navy 20+ years ago. I thought those things were pretty complex, since they used motors, electronics as well as pneumatic pressure and sensors.

There's a lot more to brakes than I thought. That brake fluid PDF file does a good job explaining how the sensor works. Thanks for your explanations as well.

[birdbarian]

I tried the brake pedal trick as well as tapping on the reservoir, and neither helped. I could see the grooves for the float on the top of the reservoir. Never noticed those before.

Wondering if I should just send off for the part. Only $13 with shipping.

[fdryer]

I'd try removing the sensor for testing now that you have info on how it works before ordering one. These things don't fail as a rule as they sit in place, sealed forever with very little environmental influence to break it. I'd be more inclined to think the brake fluid has congealed around the float, especially if fluid is dark. New brake fluid is almost colorless and readily absorbs moisture that turns fluid dark from reaction over time. Tapping the fluid container might loosen any built up deposits from old brake fluid. With well over 50k miles and one or more brake repairs, fluid is never mentioned for periodic replacement when its needed. While some may think the brake master cylinder is sealed once the cap is on, wrong assumptions of many things causes perpetuating these assumptions.

If you can, using a turkey baster to remove most of the old fluid and replacing it with fresh DOT-3 brake fluid (less than $5/qt) may correct a possible sticking float while ridding part of the bake system of old fluid. Something to consider.

Not to get off topic but the ideal time to replace brake fluid is when the brake caliper pistons are pressed back home during pad replacement; cracking open the bleed valve to allow old fluid out into a container will allow old fluid to drain out instead of being pumped back into the brake system. Once the caliper piston is homed the bleed valve is closed and the previously emptied out master cylinder that was refilled with fresh brake fluid now allows new fluid into the system without bleeding. If done right, no air enters the system. A complete bleed procedure is recommended but if testing brakes results in normal braking then bleeding may not be needed. The new fluid also flushes away any old fluid that may have congealed around the float to allow the float to rise higher where it belongs to allow the brake sensor to work properly.