A Near Strikeout

Play Ball!

1997 Ranger, 2.3L Engine, 27,000 miles

Abs light on at times

A mildly confusing problem can turn nasty when communication breaks down.

By Richard McCuistian

The guy had what seemed like a simple problem with his 1997 Ranger:  His ABS light was on. We may never know how he described it to the service writer, but “ABS light on at times.” was all that was written on the repair order.  There are many customers who just don’t offer much information, even when the service writer asks the right questions. We’ve all seen it.  The technician works for an hour or two chasing a particular noise, vibration or some other symptom, only to find that the customer’s concern was a long way from what the tech was working on.  It’s annoying to everybody.  Whatever happened, whoever was guilty, we almost struck out this time.

The Pitch

            Mechanic number one (we’ll call him Sam) drew the repair order because ABS was one of his specialties and the dispatch computer had filed the repair under his name.  He read the words “ABS light on at times,” and went to work. 

Sam had done a lot of these; ostensibly, this one would be no different. This little truck was equipped with Rear Antilock Brakes only, which have been mandated on trucks and vans since 1987.  This one was a standard RABS setup, with a small control module, a control valve with a warning lamp switch (vaguely similar to the proportioning valves of old), and a differential speed sensor in the rear end reading rear axle speed. The RABS module also monitors fluid level input. Obviously, if the fluid is low, the ABS module doesn’t need to mitigate rear brake operation, since the front brakes may be starving for juice.  If the fluid level is low, the red brake light is illuminated along with the yellow ABS light and the system is shut down by the controller.

If the control module sees a “brake applied” (from the stop lamp switch) signal on pin 11 of the module, coupled with a sudden drop in rear axle speed coming from the Differential Speed Sensor, it grabs control of the rear brakes by machine-gunning current to the isolation and dump solenoids on the RABS control valve.  The driver will feel a peculiar pulsing of the pedal that most folks are familiar with nowadays, and the rear wheels won’t slide, provided all is well with the system.

Steerrrike One!

For Sam, It would be a simple matter of yanking fuse number 9 (fuse 35 on 98 models) out of the instrument panel fuse box with the key on, jumping the “cold” side of the fuse socket momentarily to ground, and watching the codes flash out on the ABS lamp.  In this case Sam received a code 12.  Having checked the fluid level on his initial inspection, Sam pondered the symptoms.  The red brake lamp can also be triggered by the switch in the RABS valve (on the order of the old proportioning valve switches), but that would toss a flashout code 4 instead of a 12.    If the fluid sloshes during braking and the fluid level switch closes briefly, the RABS controller takes that event as an indicator that the fluid is low, and as an early warning, a code 12 will be set. 

Since this reservoir was full, Sam drew on past experience, thinking the fluid level switch had gone a little wacko and needed replacing.  The Parts Department didn’t have a reservoir in stock, so Sam ordered the part, parked the truck, and turned in the repair order. The customer picked up the vehicle and went on his way to await the arrival of the post card that would tell him his part had come in.  In the meantime, he would continue to be annoyed by the warning lamps.

Strike Two!

            A few days later, the part came in, but since Sam was swamped with front end work that couldn’t be put off, the ticket was dealt to another technician (we’ll call him Ernie) who blindly trusted Sam’s diagnosis, drew the part, and slapped it on with practiced efficiency.  Ernie made sure the pedal was nice and firm, performed a short test drive, saw no warning lamps, parked the Ranger, and turned in the repair order.  Another job well done, right?  Not quite!

Foul Ball! Time Out!

            The customer wasn’t gone very long before he was back, and boy was he hot!  He wheeled into the writeup area, skidded to a stop, and a moment later he was standing at the cashier’s window asking to talk to the service manager NOW!  He laced his request with some rather alarming but colorful metaphors, and the cashier smiled sweetly, slid her window closed, and promised (through the glass) to find someone else to keep the customer company and talk to him about his problem.  Since the service manager is out of town for the day, the cashier contacted next manager up the totem pole, (a guy we’ll call Randy), and tossed the irate motorist in his lap.

The Coach Calls The Ball

            Intense damage control strategies were under way from every quarter.   I first realized that something was “going down” with this customer when I spotted the manager having a powwow with Sam, Ernie, and the customer right there in the shop.  I happened to be at the dispatch window when Ernie walked up, having just left the powwow area. 

The service writer had already contacted the dispatcher and alerted him.  The little Ranger was back, the customer was a bit disappointed (to put it mildly), and the problem needed to be re-checked  pronto.  The dispatcher tried to give Ernie the job again, but Ernie turned it down.

            “Randy said to give that one to Richard,” Ernie tells him, bumping me in the shoulder with his fist.  This isn’t surprising.  In those days, when a delicate situation arose that had to do with a “tune-up” gone bad, electronic controllers running amok, or sparks that need to be chased, my name came up.  This time was no different.  Ernie went back to the dugout and the dispatcher thunked the ticket into the time clock, then tossed it to me. Now it was my turn at bat.  Let’s see if I could turn an RBI on this one….

Pinch Hitting

            Walking out to the writeup area, I found the customer unloading some stuff from the cab of the Ranger.  Since second and third party information is prone to cause problems, I figured to nip any communication problem in the bud.   Since the customer had spent his anger and exhausted most of his colorful metaphors on the cashier and the manager, he was pretty calm by the time I got to him. 

            “Let’s see, what do we have here?” I asked.

            “Okay, this is the deal,” he told me.  “When I first start the truck, the ABS light comes on, then goes off.  But if I push the emergency brake, the red brake light comes on and a moment later, the ABS light comes on, and it stays on until the next time I turn the key off.  That’s it. It does it every time.”  He demonstrated the problem by pressing the emergency brake.  Sure enough, the red brake light came on, followed a second later by the yellow ABS light.  He finished taking his personal effects out of the truck, figuring to leave it with us for a few days…

            I wondered if he had been so succinct in describing the problem to the service writer on the first visit.  Nobody will ever know.  And since this problem was as unusual as it was, it wasn’t surprising that it had eluded Sam and Ernie.  The park brake shares the red brake light with the ABS system, but the circuit is wired so as to prevent this warning light problem.

Eye On the Ball

            Back in the Service Bay, I tackled the problem with my young trainee in tow. The controller has fourteen pins for power, ground, inputs and outputs.  Pin 2 receives voltage through the Red ABS lamp bulb.  If for any reason this voltage is interrupted, the controller illuminates the yellow ABS lamp and shuts the system down.

    The diode in the diagram has the job of preventing pin 2 from losing voltage when the park brake is applied.  Since the voltage comes through the bulb and is effectively neutralized when the bulb is illuminated, the resistor carries the voltage to pin 2, effectively allowing the red brake lamp to burn while still supplying the controller with the voltage needed.

            I unplugged the master cylinder reservoir and jumpered the dark green-yellow and tan-light green wires with a short piece of solder.  This effectively bypasses the reservoir switch and eliminates that part of the circuit, narrowing things down. Connecting my voltmeter between the piece of solder and ground, I could monitor the 12 volts on the circuit leading to pin 2.  When the park brake was applied, the voltage disappeared.  It shouldn’t have.  Here was the problem, but what was the reason for it?   Perhaps the diode had gone sour and was carrying voltage both ways.

            On the early Rangers, this diode and resistor were heat shrinked and taped into the harness.  On this one, however, they’re both found in the fuse box under the hood dubbed “Power Distribution Center” in Ford’s literature, and generally called the “PDC.” 

There are two diodes (one is the Powertrain Control Module power relay diode, which will create a no-start if removed) and the resistor. Their terminals are turned in such a way that a fuse can’t be inserted by accident in any of these positions, and the diodes can’t be inserted backwards.  The two black ones pictured are diodes, while the resistor is the white one (see photo). I swapped the PCM and antilock diodes around, but to no avail.  I knew something was rotten in Denmark when my trainee told me the ABS lamp illuminated as soon as I removed the diode.  That shouldn’t have happened, and it offered an important clue as to the source of the problem.  The resistor element had to be open, since it provides voltage when the bulb is illuminated. Removing the diode would be like illuminating the bulb.  I unplugged the resistor element, clicked my meter to the ohmmeter setting and found that the resistor element was completely open.  It only took a moment to grab an old resistor out of my toolbox and use it to jumper the cavity.  The problem instantly evaporated.

Runner Batted In…Barely

            Had the customer become disgusted enough, he might have taken the problem to another shop.  I hate strikeouts like that.  This problem wasn’t so terribly complicated, but somebody dropped the ball in the writeup area.  Whether it was the customer or the service writer remains to be seen.  Had communication been better between the customer and the service writer, this would have been a home run from the first swing of the bat.

 R.W.M.