Rear ABS light on.....worry about or forget about it?
 

Howdy Guys!!:-drink

Long time no post, I know, I know.... but two wee cowgirls have kept me super busy.

I was driving home tonight, in a thunderstorm in the middle of WINTER, when all of a sudden my Rear ABS light pops on. Hummmm.... me thinks a wire might be needing fixing, but what if it is something more sinister??? Is there a way to pull codes for the Rear ABS light??

So here I am.... picking the brains of the Aero-Gurus8D.....

I purposely removed the fuse for my Rear ABS on my 90 3.0 2WD Aero 10 years ago because the ABS was malfunctioning. Its not a problem for me, but the only thing is that on a damp street if i need to romp on the brakes the rears lock up but the front stays under control. Its no big deal so I would just remove the fuse and forget about them, unless you want to spend the $$$ to fix it....

Rear abs
 

I kind of did the same on my 93 3.0. Sometimes on damp or rainy days one wheel in the back locks up a bit till I hit the brakes 3-4 times going up the street then it's fine. Only does it when I first start out in the morning and does'nt do it very often, been doing that for over 2 years now. T

howdy Cow Momma
how ya'll been and those 2 young heifers?
i see your hubby is going to be crawling under your Aero and doing some brake work.

Ford RABS school--after you get the fail code we'll procede from there with specific code diagnosis

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.

===========
System Pre-Check

The RABS II uses both the red BRAKE and yellow REAR ABS instrument panel warning lights to alert the driver to a system malfunction. Both lights must be working properly to assist in concern diagnosis. The steps listed below must be followed prior to beginning the RABS II diagnostic procedure.

NOTE:
This repair procedure is written for REAR ABSII (RABS II) systems (as opposed to REAR ABSI [RABS I] systems). RABS II systems are standard for 1992 and 1993 Aerostar, as well as 1993 Rangers. In the event that you are not sure if you have a RABS I or a RABS II system in your vehicle, check the module part number. RABS II module part numbers will begin with either: F29F-2C018- or F37F-2C018-. All other part numbers should be considered to be a RABS I. If you have a RABS I module, you must refer to the repair manual for that model year vehicle.


Vehicle Setup

For 4-Wheel Drive vehicles, shift into 2-Wheel Drive. Drive the vehicle to a level area, and place the shift lever in PARK for automatic transmissions and NEUTRAL for manual transmissions. Turn the ignition off, set the parking brake and turn on the running lamps. Place blocks behind the wheels.

WARNING:
PLACE BLOCKS BEHIND THE REAR WHEELS AND IN FRONT OF THE FRONT WHEELS TO PREVENT THE VEHICLE FROM MOVING WHILE THE SYSTEM PRE-CHECK IS BEING DONE.

Release the parking brake and continue to Brake Light Self-Check.


Brake Light Self-Check

The Red BRAKE warning light is used to indicate a low fluid level condition or parking brake applied condition. To check this light, insert the key in the ignition lock cylinder and turn it to the START position. The light should glow in this position. If it fails to glow, service the electrical system as required. Go to «System Pre-Check Test B, Red Brake Light OFF and Does Not Self-Check.»

Allow the key to spring back from the START position to the RUN position. At this time the red BRAKE light should turn off. If it does not turn off, recheck the parking brake switch to make sure that it is fully dis-engaged. If the red BRAKE light is still ON, service the Base Brake System. In the event that the red Brake light remains on, go to «System Pre-Check Test E» , Red Brake Light ON.


Rear Anti-lock Bulb Self-Check

The yellow REAR ABS warning light is used to indicate a malfunction and a deactivation of the RABS II. To check this light, first follow the procedure above for Brake Light Self-Check, and allow the key to spring back from START position to the RUN position. The REAR ABS light should perform a self-check by glowing for approximately two seconds and then turn off. If it fails to glow, service the RABS II lamp electrical system. Go to «System Pre-Check Test A» ,Yellow REAR ABS Light OFF and Does not Self-Check. If it turns back on and does not flash, then a system concern has been detected. Refer to procedures for obtaining diagnostic trouble code.


Rear Anti-lock Bulb Automatically Flashing After Bulb Self-Check

If the yellow REAR ABS warning light begins to flash, this indicates that the Keep Alive Memory (KAM) power to the RABS II module has been disrupted. If this condition occurs, service the RABS II KAM power system as required. Go to «System Pre-Check Test C,» Yellow REAR ABS Light Self-Check OK, but light Automatically Begins Flashing.


Obtaining the Diagnostic Trouble Code (DTC)

NOTE:
Verify the ignition switch is in the RUN position. (NOTE: 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 if servicing an Aerostar with locking terminals:

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

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

3. 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.

4. Separate the two connector housing halves by pushing the tool handle towards 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 flashout code when diagnostics is 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.


Clearing the Keep Alive Memory (KAM)

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 re-assembled to provide KAM power to the RABS II module. If at this time a valid code has been obtained, go to the appropriate pinpoint test for that code.

Funny you say that, usually on damp mornings I sometimes make a lot of noise just backing out of my driveway and going into D. I'll be backing out and when i hit the brakes all of a sudden the rears lock up and screech me to a stop, LOL. But once the brakes are warmed up they work just fine. :)

First check your brake fluid level. Then you may well find a problem in the combination valve. Does the pedal behave normally or soft? (sinks gradually to floor?)

Check something simple first: Are the brake lights working?

On both of my Aero's the ABS light came on, both turned out to be the plug in on the side of the MC had a wire loose. Repaired the wire plug and no more problems.

Thanks everyone!! I will have hubby do some basic checks and will try to pull the codes.... may be a few days, we've been sick with a really bad cold/flu-like virus--yuck!!

The ABS light comes on to tell you that the computer has detected a fault in the RABS system and has disabled it. This will not affect the normal brakes at all. Just make sure you check the fluid level.

Check the rear brake lights. One of them being out may cause the light on the dash. Also, pull the drums and check the brakes. On mine, the light came on due to the wheel cylinders leaking.

Good luck.

Okay Guys-- I've got a new symptom for ya......

So, I'm still sipping tea and eating toast when my friend calls me with a muti-emergency. So I have to drive the Aero because hubby is not home yet. Everything is fine till I go to leave her house---and my muffler falls off!! :eek: The flexpipe had finally rusted through!! :-banghead So, I call DH to come and rescue me and the girls.

After DH gets the muffler wired up, we take off with him following close behind. After about a mile he calls me and asks "Are you riding the brakes?" Me "Nooo...why?" Hubby: "Because your brake lights are continueously ON!!" Me: "Greaaaatttt...."

And what I had not told him was that my Rear ABS idiot light *was* OFF until I pulled out of her driveway, then *BLAM* It came on again!!!

So that is the latest and greatest.... I guess I would have never realized I had a problem unless the muffler had fallen off!! :rolleyes::rolleyes::rolleyes:

broken sticking brake light switch on brake pedal arm or

water moisture corrosion stuck master cylinder, combination valve, ABS valve and/or rear wheel cylinders.

Well that explains why the ABS light was on. Fix the brake lights and you should not have the ABS light on again.
Look under the dash and at the brake pedal and you should see a small switch, operated by the brake pedal arm. With the brake lights on unplug the electrical connector from the switch. If the lights go out then replace the switch.

Well Guys, you are probably not going to believe this.....

So DH started to troubleshoot my continuous brake lights on issue. Discovered the brake lights were ONLY continuously ON when the headlights are also ON. *Hummmm*.... So off he went to troubleshoot some more.... and guess what he figured out???? Guess!! You won't believe it.....



:-huh:-huh:-huh







Give up yet???
:confused::confused::confused::confused::confused: :confused:





The brake light/tail light BULB ....... well, one of the two filaments burned off and ended up landing on the other filament, thus creating a "connection" or bridge so to speak. So the two lights continued to work "normally"--well sort of....., but was constantly ON when the headlights were ON.... so in essence it was a "short in the system"!!!! (I will try to post a pic of the bulb if I can get a good pic of it....)

:-bigparty:-bigparty:-bigparty



I just hope that maybe that is the reason for the Rear ABS light to be on too..... keep fingers and toes crossed for us!!! It's getting cold again around here and DH really doesn't want to do major repairs in freezing cold!!!