Anti lock warning light

[haydad]

1994 TC, in the past 3 months, three times when the brakes were pressed they grab very abruptly, the anti lock light flashes three times, blinks three times and the light stays on. The light goes out when the car is turned off and doesn't come on unless this even occurs again.

Any thoughts?

Thanks in advance

[Towncar]

Most of these ABS problems are traced back to wheel sensors or wiring to the wheel sensors. If your ABS light is on you'll have to have the stored fault codes pulled with an appropriate scanner, and take actions depending on that result.

This service manual is available on my web site, here a quote:

«1994 Town Car/Crown Victoria/Grand Marquis Table of Contents»
«Group 06: BRAKE SYSTEM»
«Section 06-09: Brake System, Anti-Lock»
«DESCRIPTION AND OPERATION»

Brakes, Anti-Lock

Anti-Lock Brake System (ABS) operates as follows:

• When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the inlet ports.
  
• This pressure is transmitted through four normally open solenoid valves contained inside the anti-lock hydraulic control unit, then through the outlet ports of the anti-lock hydraulic control unit to each wheel.
  
• The primary (rear) circuit of the brake master cylinder feeds the right front and left rear brakes.
  
• The secondary (front) circuit of the brake master cylinder feeds the left front and right rear brakes.
  
• If the anti-lock brake control module senses that a wheel is about to lock, based on sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.
  
• The anti-lock brake control module then looks at the sensor signal from the affected wheel again.
  
• If that wheel is still decelerating, it opens the normally closed solenoid valve for that circuit. This dumps any pressure that is trapped between the normally open valve and the brake back to the hydraulic control unit reservoir.
  
• Once the affected wheel comes back up to speed, the anti-lock brake control module returns the valves to their normal condition allowing fluid flow to the affected brake.
  
• The anti-lock brake control module monitors the electromechanical components of the system.
  
• Malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power assisted braking remains.
  
• Malfunctions are indicated by one or two warning indicators inside the vehicle.
  
• Loss of hydraulic fluid in the hydraulic control unit reservoir will disable the anti-lock system.
  
• The 4-wheel anti-lock brake system is self monitoring. When the ignition switch is placed in the RUN position, the anti-lock brake control module will perform a preliminary self-check on the anti-lock electrical system indicated by a three to four-second illumination of the amber CHECK ANTI-LOCK BRAKE indicator in the instrument cluster.
  
• During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.
  
• Each time the vehicle is driven, as soon as vehicle speed reaches approximately 30 km/h (19 mph), the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time a mechanical noise may be heard. This is a normal function of the self-check by the anti-lock brake control module.
  
• In most malfunctions of the anti-lock brake/traction assist system, the amber CHECK ANTI-LOCK BRAKE and/or red BRAKE indicator(s) will be illuminated.
  
• The sequence of illumination for these indicators combined with the actual symptoms, can determine the appropriate diagnostic tests to perform.
  
• However, most malfunctions are recorded as a diagnostic trouble code (DTC) in the anti-lock brake control module memory and assist in pinpointing the component needing service.

[Bearfoot]

I had that problem - anti lock warning light on intermittantly. Ford charged $90 just to read the codes! They included that in the $240 to replace the module for the LF wheel -- wasn't that kind of them?

[haydad]

Can the service codes for the ABS be pulled by jumping the computer plug and reading the flashes on the dash warning light like can be done for some of the service codes?

Thanks for the replys

Haydad

[Bearfoot]

My understanding is that there is a different computer plug, for a different computer for the ABS. I could be all wet.

[haydad]

Is the ABS light different from the antilock light?

Are the wheel sensors items that can be replaced by a mechanically inclined guy or is this an item that should go into the shop?

Thanks

[Towncar]

Originally Posted by haydad

Is the ABS light different from the antilock light?

Are the wheel sensors items that can be replaced by a mechanically inclined guy or is this an item that should go into the shop?

Thanks

Yes, Antilock and ABS are separate fault lamps however, they do share some of the same components to function properly... one of those is the wheel sensors.

Did you get my 1993/1994 FSM from my website? It details the sensor replacement procedures.

There's some talk, a TSB too, saying that many of these type of problems are a bad connection to one (or more) of the sensors. The recommendation is to unplug each sensor and clean the connectors, spray some stuff in there to further protect it, inspect the wire harness condition, and re-assemble. Since you don't know which one might be the problem, this can be tedious. The FSM (others may know this) tells the resistance values of the sensors for testing them.

Also, the stationary sensor 'reads' a spinning ring gear, that air space between the two may be clogged with brake dust, you'll have to remove the wheels to clean that out.

Here's some basic overview shots; more detail is available from that FSM: