94 Brakes
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Freshman User
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94 Brakes
My brake light and rear ABS light cam on, went to have it checked out, I needed new brakes. Put on rotors/pads/calipers/wheel bearings/bleed the complete system. Rear brakes are fine, just needed adjusting. The Brake light and the rear ABS light are still on.
Replaced a sensor in the rear end, lights still on.
Replaced the master cylinder, lights still on.
I checked the wiring connections, and as far as I could see, all is fine.
What could be the problem? and any suggestions? where to look?
Thank you,
Replaced a sensor in the rear end, lights still on.
Replaced the master cylinder, lights still on.
I checked the wiring connections, and as far as I could see, all is fine.
What could be the problem? and any suggestions? where to look?
Thank you,
Lead Driver
Joined: Sep 2003
Posts: 7,019
Likes: 210
From: SoCal
This happened to mine when the rear brake light bulbs burned out. It also disabled the cruise control, torque converter lockup, and E4WD. I also replaced the speed sensor in the rear axle (it was the cheapest of the 3), but that obviously didn't solve the problem. A couple of 2357 bulbs solved everything.
Lead Driver
Joined: Sep 2003
Posts: 7,019
Likes: 210
From: SoCal
When you say you needed new brakes, what exactly were needed?
Since they bleed the system, I'll assume that they checked the level switch that it's not stuck.
Here's another WAG: Did they check the shuttle valve in the master cylinder proportioning valve? Maybe your 94 is different from my 90 model, but on mine it's in the front of the MC. It's pretty easy to check; do a continuity test between ground and one of the pins on the sensor screwed into the front of the valve. There should be no conduction, but if there is, the valve has "shuttled" to one side or the other. This usually happens from either the front or rear circuit leaking. Or when someone is bleeding the brakes, they got aggressive with the pedal while one of the bleed screws were open. I use a multimeter with a beeper for continuity to test the circuit, and open either a front or rear bleeder while I pulse the pedal to try to push the shuttle valve back to center.
The level switch and the shuttle valve switch form part of the brake check circuit, and if either one is not properly connected, it will trigger the brake light.
Since they bleed the system, I'll assume that they checked the level switch that it's not stuck.
Here's another WAG: Did they check the shuttle valve in the master cylinder proportioning valve? Maybe your 94 is different from my 90 model, but on mine it's in the front of the MC. It's pretty easy to check; do a continuity test between ground and one of the pins on the sensor screwed into the front of the valve. There should be no conduction, but if there is, the valve has "shuttled" to one side or the other. This usually happens from either the front or rear circuit leaking. Or when someone is bleeding the brakes, they got aggressive with the pedal while one of the bleed screws were open. I use a multimeter with a beeper for continuity to test the circuit, and open either a front or rear bleeder while I pulse the pedal to try to push the shuttle valve back to center.
The level switch and the shuttle valve switch form part of the brake check circuit, and if either one is not properly connected, it will trigger the brake light.
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The pads were worn and groves started in the rotors, so I replaced everything.
They did bleed the brakes. We installed a new master cylinder because the original was still there, and figured the switch in there and the age it was time, but it didn't shut the light off.
I will check on the level switch.
Electrical tests yesterday and didn't find the problem yet.
Will the level switch trigger both the brake light and the rear ABS light?
Thank you!
They did bleed the brakes. We installed a new master cylinder because the original was still there, and figured the switch in there and the age it was time, but it didn't shut the light off.
I will check on the level switch.
Electrical tests yesterday and didn't find the problem yet.
Will the level switch trigger both the brake light and the rear ABS light?
Thank you!
Post Fiend
Joined: Apr 2005
Posts: 5,720
Likes: 5
From: Washington state
There is an extensive RABS system troubleshooting section covering warning lights, RABS failures ad naseum in the real Ford Aerostar service manual. It covers an extension section on error code reading technique and code troubleshooting leading to the failed component. Be sure to get the EVTM section, not all include it.
My CD copy has long since died.
Believe the 94 has the upgraded separate combination valve with the error light producing shuttle switch mounted below the MC and the first thing connected to the MC brake fluid pressurized output
be aware there is a high pressure spring behind the screw in plug and easily lost rubber plug in the shuttle section of the CV. unit is a water crud collector, often has to be taken apart and cleaned with brake cleaner and no water alcohol. water diluted alcohol corrodes brake parts
My CD copy has long since died.
Believe the 94 has the upgraded separate combination valve with the error light producing shuttle switch mounted below the MC and the first thing connected to the MC brake fluid pressurized output
be aware there is a high pressure spring behind the screw in plug and easily lost rubber plug in the shuttle section of the CV. unit is a water crud collector, often has to be taken apart and cleaned with brake cleaner and no water alcohol. water diluted alcohol corrodes brake parts
Lead Driver
Joined: Sep 2003
Posts: 7,019
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From: SoCal
Forgot about that corrosion business. Sometimes the shuttle valve sensor gets a ball of green crud on it that shorts it out to the valve, causing the brake light to come on. The ABS will not work with any kind of brake error present, so yes, a problem with either the float switch or the shuttle valve switch will trigger the brake light, which can then cause the ABS light to come on.
It sounds like the 94 model may require extra care to remove and clean the sensor. On mine, I could almost unscrew it with my fingers, and pull it out. Then clean the corrosion off the sensor, and from inside the hole that it screws into. Use a little teflon tape on the threads before putting it back in to help seal out water.
It sounds like the 94 model may require extra care to remove and clean the sensor. On mine, I could almost unscrew it with my fingers, and pull it out. Then clean the corrosion off the sensor, and from inside the hole that it screws into. Use a little teflon tape on the threads before putting it back in to help seal out water.
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Fleet Mechanic
Joined: Apr 2003
Posts: 1,460
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From: Florida
I have also heard that it takes a number of bleeds to get the darned RABS light to go off. Mine is on too, a total pita. I even replaced the fluid reservoir, light still on.
I gave up and removed the bulb, the brakes are fine.
I gave up and removed the bulb, the brakes are fine.
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Post Fiend
Joined: Apr 2005
Posts: 5,720
Likes: 5
From: Washington state
some of us live near the sea coast, drive thru major winter coastal storms, drive on ocean beaches. corrosion from salt is real here and in locals where winter road salt is required.
not all of us are trapped in the Cali. sun smog.
I can actually see Russia on a clear day
not all of us are trapped in the Cali. sun smog.
I can actually see Russia on a clear day
Forgot about that corrosion business. Sometimes the shuttle valve sensor gets a ball of green crud on it that shorts it out to the valve, causing the brake light to come on. The ABS will not work with any kind of brake error present, so yes, a problem with either the float switch or the shuttle valve switch will trigger the brake light, which can then cause the ABS light to come on.
It sounds like the 94 model may require extra care to remove and clean the sensor. On mine, I could almost unscrew it with my fingers, and pull it out. Then clean the corrosion off the sensor, and from inside the hole that it screws into. Use a little teflon tape on the threads before putting it back in to help seal out water.
It sounds like the 94 model may require extra care to remove and clean the sensor. On mine, I could almost unscrew it with my fingers, and pull it out. Then clean the corrosion off the sensor, and from inside the hole that it screws into. Use a little teflon tape on the threads before putting it back in to help seal out water.
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