Just replaced the front brake calipers and pads on our 1995 aerostar.When I cranked it up the light came on for the rear abs.Ive already bled the front brakes removing any air.Any idea what caused this?

 

You will probably need to pull a code. One common failure is the speed sensor. However, you say you did the brakes yourself? Did you compress the calipers? If so, you may have forced dirty and contaminated brake fluid through the ABS valve, blocking or jamming it. We will need to find ou what the stored code is to determine what has happened. I do not know the procedure for pulling the code, but I'm sure there are several people here who do.

 

pull the black plastic screw in switch on top of the combination/proportioning valve and clean it of all dirt, corrosion and debris.
pull the end cap off the comb. valve, remove the piston and clean interior with new brake fluid
careful, the piston and end cap are under heavy spring pressure and there is a small rubber end center plug easily lost.

this resets the switch to a center nuetral position after having been forced to limit lock in the muck and debris by the false front brake failure induced by the caliper pistons being forced back in

 

To pull the code you need to go to Autozone or find someone who has a scantool. They can read the code in less than 5 mins, does yours have a Datalink (obdII) connector or the older obd1 connector ?

The older connector will allow you to access the codes by counting the blinks on a test lamp if you rig one up. There is a self test input, which allows this; the Haynes manual goes into quite some detail on how to perform this & also gives the code definitions. If not you can get an OBD1 code puller for about $30 or so. Not sure if the OBD1 system integrates ABS into the fault code list.

Addendum, Just checked out the fault code list for above , but dont see any ABS related codes. In the Haynes manual it says if the rear ABS light comes on take the vehicle to a Ford dealer!!!

All the best, Aeroman

 

Rear Anti-Lock Brake System (RABS II)


How The Circuit Works


New Features for RABS II
Unlike early versions of RABS Modules, the RABS II Module remembers the diagnostic code even after the vehicle has been turned off. This feature is known as Keep Alive Memory (KAM). Note that while the diagnostic test is being performed, the key must be turned to the on position, otherwise the code will be lost.

If the RABS II self-test detects no faults, the RABS II Module will flash out a code of 16. This is normal and indicates that the RABS II system is functioning correctly.

Operation
The Rear Anti-lock Brake System (RABS II) continuously monitors rear wheel speed with a sensor mounted on the rear axle. When the teeth on an excitor ring (mounted on the ring gear) pass the sensor pole piece, an AC voltage with a frequency proportional to the average rear wheel speed is induced in the sensor circuit. Should an impending lockup condition occur during braking, the RABS II system modulates hydraulic pressure to the rear brakes, inhibiting rear wheel lockup.

When the brake pedal is applied, the Rear Anti-lock Brake (RABS II) Module senses the drop in rear wheel speed. If the rate of deceleration is too great, indicating an impending wheel lockup, the Rear Anti-lock Brake (RABS II) Module activates the isolation valve solenoid, causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders are isolated from the master cylinder, and the rear brake pressure cannot increase. If the rate of deceleration is still too great, the Rear Anti-lock Brake (RABS II) Module will energize the dump valve solenoid with a series of rapid pulses to bleed off rear wheel cylinder fluid into an accumulator built into the RABS II valve. This will reduce the rear wheel cylinder pressure and allow the rear wheels to spin back up to vehicle speed. Continuing under Rear Anti-lock Brake (RABS II) Module control, the dump and isolation valve solenoids will be pulsed to keep the rear wheels rotating while maintaining high levels of deceleration during braking.

At the end of the stop, when the operator releases the brake pedal, the isolation valve solenoid deenergizes, and any fluid in the accumulator is returned to the master cylinder. Normal brake operation is resumed.

System Self Test
The Rear Anti-lock Brake System (RABS II) has self-test capabilities much like those in other electronic control systems. Two warning lamps are located in the instrument panel to alert the driver to a system malfunction: a red BRAKE warning lamp and a yellow REAR ABS or ANTI-LOCK warning lamp. The red BRAKE warning lamp indicates a low fluid level condition or parking brake ON; the yellow REAR ABS or ANTI-LOCK warning lamp will light only if the Rear Anti-lock Brake (RABS II) Module detects a malfunction in the system that will affect the operation of the system, or for approximately two seconds during ignition ON or engine cranking as a circuit prove-out.

The self-test feature contains thirteen codes that indicate areas of malfunction. When a malfunction is detected, the control module will shut down the system and the yellow REAR ABS or ANTI-LOCK warning lamp will come on. This will permit normal braking. A code will be set in the system memory that can be retrieved by momentarily grounding the diagnostic pigtail and counting the flashes of the yellow light. If there is more than one fault, only the last recognized fault will be retained and flashed. Additional codes will output only after the first fault is corrected. For further information on the code system, refer to Section 06-09 of the Service Manual.

REFERENCE :For diagnostic information, refer to «Section 06-09A » of the Service Manual.

Aerostar

The Aerostar RABS II consists of the following components:

l RABS II module mounted to the driver's side of the doghouse under the instrument panel.

l Dual solenoid electro-hydraulic valve located on the fender apron below the master cylinder.

l Speed sensor and speed sensor ring located in the rear differential housing.

l RABS diagnostic connector located on the main wire bundle, inside driver's side of cab, under the dash connected to mating battery power connector.

l Yellow REAR ABS warning light in the instrument cluster.

l Diode/Resistor Element located behind the instrument panel, below the left-hand side of the radio, approximately 9 cm (3.5 inches) from the G200 instrument panel ground. Refer to the EVTM Cell 151-6 for the locator view.

l Sensor test connector with cap located forward of the 53 pin connector on the left hand fender apron.

Diagnostic Trouble Codes (DTC), Retrieving


NOTE: Verify the ignition switch (11572) is in the RUN position (engine does not need to be running). Next, locate the black RABS II diagnostic connector. The diagnostic connector has two mating halves (one of which has a black/orange wire connected to it). Disconnect the two halves.



NOTE: Some Aerostar vehicles were built with locking terminals in the diagnostic connector, making it difficult to disconnect the two mating halves.


Use the following procedure Steps 1 through 4 if servicing an Aerostar with locking terminals.


For Ranger go to Step 5.

Lift the latch on the female housing to disengage the locking mechanism.

Attempt to separate the two connector halves until the terminals lock.

On the top portion of the connector housing, opposite the mounting tabs, there is a small hole. Insert a narrow blade screwdriver or scribe type tool into the hole until it stops.

Separate the two connector housing halves by pushing the tool handle toward the black/orange wire.

Attach one end of a jumper wire to the black with orange stripe wire side of the diagnostic connector.

Momentarily ground the opposite end of the jumper wire by connecting it to a good chassis ground for 1-2 seconds.

Grounding this wire should start the REAR ABS lamp flashing. If grounding this wire does not start the REAR ABS lamp flashing, go to System Pre-Check Test D, Yellow REAR ABS Light Self-Check OK, but No Diagnostic Trouble Code When Diagnostics started .

CAUTION: Care must be taken to connect only the black/orange stripe wire to ground. Connecting the mating connector wire to ground will result in a blown fuse.

The code consists of a number of short flashes and ends with a long flash. Count the short flashes and include the following long flash in the count to obtain the code number. For example, three short flashes followed by one long flash indicates diagnostic trouble Code 4. The code will continue to repeat itself until the key is turned off. It is recommended that the code be verified by reading it several times. This code will be used later for system repair instructions, it should be written down for future use. A diagnostic trouble code of 16 will be obtained when the module detects normal system operation.


Diagnostic Trouble Codes (DTC), Erasing

The last step of the System Pre-Check always includes clearing the keep-alive memory (KAM). To do this, simply turn off the ignition while the diagnostic connector halves are separated as described in the procedures for obtaining the diagnostic trouble code above, after which the diagnostic connector should be reassembled to provide KAM power to the anti-lock electronic control module. If at this time a valid code has been obtained, go to the appropriate pinpoint test for that code.




RABSII test connector located >Behind LH side of I/P, taped to main harness
black 1 wire connector