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intermittent ABS/ASR/Brake light

94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
I have a 94 and almost every time I drive it the ABS/ASR and Brake lights flash on the dash. They do not stay on. I had the codes read last summer and I am thinking he said it was a wheel speed sensor or he suspected that's what it was but with OBD1 it's limited on what you can find out. Today I'm looking at the connections on at the front sensors. They all look old but what I noticed more was that there is a single black wire on the master cylinder which is wet and almost partially bare covered in brake fluid. I took the car to Big O two days ago to have the wheel bearings and ball joints looked at because I have one front drivers side tire that is wearing on the inside. They couldn't find anything wrong. Said new tires and an alignment. This cars front end seems to be getting light when I get up about 80mph. Hasn't always done this. I hear pops and cracks when I turn slow, sounds like a ball joint. Back to my question about the lights flashing. I think this wire is a pressure switch. If so and its leaking would this cause those lights to flash on the dash? I need to find a good mechanic that knows these cars here in Indiana.
 

94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
I have a 94 and almost every time I drive it the ABS/ASR and Brake lights flash on the dash. They do not stay on. I had the codes read last summer and I am thinking he said it was a wheel speed sensor or he suspected that's what it was but with OBD1 it's limited on what you can find out. Today I'm looking at the connections on at the front sensors. They all look old but what I noticed more was that there is a single black wire on the master cylinder which is wet and almost partially bare covered in brake fluid. I took the car to Big O two days ago to have the wheel bearings and ball joints looked at because I have one front drivers side tire that is wearing on the inside. They couldn't find anything wrong. Said new tires and an alignment. This cars front end seems to be getting light when I get up about 80mph. Hasn't always done this. I hear pops and cracks when I turn slow, sounds like a ball joint. Back to my question about the lights flashing. I think this wire is a pressure switch. If so and its leaking would this cause those lights to flash on the dash? I need to find a good mechanic that knows these cars here in Indiana.
I forgot to mention that they did say at Big o that the front drivers side brakes were wearing more then the passenger side like they were getting stuck or hung up
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
The wire leading to the sensor in the side of the master cylinder reservoir is the low brake fluid sensor.

If you service ABS and service ASR lights are on, you need to find out what the problem is.

There is an article here on the CAC which covers C4 ABS/ASR service. Click here to see that story.
 

94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
Thank you

Thank you Hib! With any luck I can find someone who knows how to check it and not just throw parts at it. I did get ahold of one guy locally who is really good with these cars. All three lights flash up and go off after a second or two, Its the abs, the asr and the brake. I was told that the system does this when one wheel sensor sends back a signal that is off. With the wire on the master cylinder being wet with brake fluid, I'm thinking it's safe to say that it's leaking to. The two wire plug is on the outside of the cylinder and this wire is on the engine side. felt like part of the wire was bare also. I had an alignment guy tell me last summer he thought the wheel bearing was causing my inside drivers side tire to wear but I had another tell me it was the ball joint and had the tire shop tell me they couldn't find anything. I finally have the cash to get something done with it. could any of this abs situation have anything to do with the front drivers side brakes wearing more then the other side?
 

ecss

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Joined
Nov 27, 2004
Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic
I forgot to mention that they did say at Big o that the front drivers side brakes were wearing more then the passenger side like they were getting stuck or hung up

If you have a switch screwed into the plastic brake fluid reservoir that is the low brake fluid switch.
The service manual says if you have low brake fluid and the switch closes, it will turn on the Brake indicator and disable ABS/ASR so no air gets into the brake system.

The pressure differential switch is screwed into the metal body of the master cylinder. If the pressure differential switch triggers, supposedly it won't reset until the pressure difference in the circuit is repaired. It also turns on the Brake indicator but I'm not sure if the ABS/ASR are disabled.

If the pressure differential switch has fluid coming from it the master cylinder needs to be replaced or rebuilt if a rebuild kit is available.
 
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94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
If you have a switch screwed into the plastic brake fluid reservoir that is the low brake fluid switch.
The service manual says if you have low brake fluid and the switch closes, it will turn on the Brake indicator and disable ABS/ASR so no air gets into the brake system.

The pressure differential switch is screwed into the metal body of the master cylinder. If the pressure differential switch triggers, supposedly it won't reset until the pressure difference in the circuit is repaired. It also turns on the Brake indicator but I'm not sure if the ABS/ASR are disabled.

If the pressure differential switch has fluid coming from it the master cylinder needs to be replaced or rebuilt if a rebuild kit is available.

Thank you!! I hope you're right and it's just the master cylinder. My kids in college and when I was told about the wheel sensor and saw how much they were, it's taken forever to come up with the cash to have this looked at and fixed. I need tires to so if I can get off easy on this one I may get those 17/9.5 and 17/11 a molds I've been looking at. I'll keep everyone posted on what happens so if this happens again someone else can use the info. My fingers are crossed. Hopefully he can look at in the next couple of weeks
 

ecss

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Joined
Nov 27, 2004
Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic
The brake wear problem on the front could be related to the master cylinder but could also be a bad caliper or bad rubber hose from the caliper to the metal brake line.

You should repair the master cylinder then go from there.

The posted ABS article described how you can pull ABS codes by using a piece of wire.



Connect either pin 4 or pin 5 which are both ground to pin 12 on the 16 pin OBD2 style diagnostic connector.
Turn the ignition On.
Look at the speedometer LCD and any trouble codes for the different modules are displayed on the LCD

Module 1 Central Control Module
Module 4 PCM
Module 9 ABS/TSC
Not sure on a 94 but you may see Module A which is the air bag system

Here's a picture of the Master Cylinder.
Item 24 is the differential switch
Item 26 is the low fluid level switch

 
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94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
Thanks for the information! I went out and checked it out today and the wire that has the one black or brown wire with tan or white stripe and is missing over an inch of insulation is actually on the frame of the master cylinder but was dry this time when I looked at it. It hasn't been driven for a few days. I pulled the codes and I got a c 12
 

ecss

Well-known member
Joined
Nov 27, 2004
Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic
So no codes for module 9?

Make sure the brake fluid level is at the full mark.
Disconnect the electrical connector going to the Low brake fluid switch.
If the Brake light indicator continues to randomly come on, the differential pressure switch is indicating something is wrong with the master cylinder.
 

94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
I went back out and drove it. There is fluid coming through the pressure switch but the level is still full.
 

ecss

Well-known member
Joined
Nov 27, 2004
Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic

94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
Thank you! That explains a lot but could it make the light come on while driving without applying the brakes and bring on the abs and srs lights intermittently you think? The master cylinders obviously bad. Just curious if it could still be something else like a wheel cylinder to
 

ecss

Well-known member
Joined
Nov 27, 2004
Messages
649
Location
Windsor Mill, MD
Corvette
89 Brilliant Red Metallic
Uneven tire wear indicates excessive wear of a component which has changed the wheel alignment or the wheel alignment has changed from an impact such as hitting a pot hole.

Since you have uneven wear on one tire only.
Jack up that wheel.

Check the ball joints, tie rods, steering rack or wheel bearings by manually moving the tire/wheel.
Play in the 12 and 6 o'clock position indicates ball joints.
Play in the 3 and 9 o'clock indicates tie rods and for the front end the steering rack.
Play in all directions wheel bearing.
Also visually check the A arm bushings are in good shape.

Examine the front and rear fiberglass springs for delamination or cracks.

Have the shock absorbers ever been replaced?

As for the difference in front brake pad wear it could be the caliper not retracting causing the pads to drag on the rotor or the inner lining of the rubber brake hose is starting to fail which restricts the brake fluid flow when the caliper retracts as the brake pedal is released. I don't see how the master cylinder could be causing the uneven front brake pad wear problem


These are things you can easily do in a couple of hours.
Otherwise you're at the mercy of a mechanic who may be training on your vehicle. :upthumbs

If you do get an alignment, make sure you get a print out showing all the specs.
 
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94conv.

Well-known member
Joined
Jun 16, 2003
Messages
446
Location
Indiana
Corvette
1994 red convertible
Thank you! I really appreciate all this information. That's a ton of help and I'm going to check the front end out tonight when I get home. Thanks again!
 

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