TROUBLESHOOTING THE TEVES II ELECTRO-HYDRAULIC BRAKING SYSTEM USED ON THE 1987-88 TURBO COUPES
By Jeff Korn
The 1987-88 Turbo Coupe, as well as the early Thunderbird Super Coupes and some Lincolns from the era, use a Teves II electro-hydraulic system to proving both power braking and antilock braking. Unlike modern ABS systems that use a standard vacuum brake booster and a separate hydraulic control unit (HCU) to provide the ABS, the Teves II system incorporates both the power brakes and ABS integrated into the master cylinder. None the less, the power braking part of the system and the ABS part of the system are nearly 100% independent of each other. If there is a failure of the ABS part of the system due to a failed wheel speed sensor, open or shorted solenoid valve, etc, the ABS computer will disable the antilock part of the system, and turn on the yellow ABS light on the dash. If the ABS part of the system is disabled, power braking will not be affected in any way. This means that a loss of power braking has nothing to do with the ABS computer, wheel speed sensors, etc. This article will discuss troubleshooting the power brake part of the braking system only. The ABS part of the system is much more difficult to troubleshoot, and will not be discussed here.
One relatively common problem with the braking system is a loss of power braking (often referred to as a “hard pedal”), accompanied by the red BRAKE and yellow ABS dash lights illuminating. Another not as common problem is the BRAKE and ABS lights illuminating briefly under hard or repeated braking. These, and a few other related problems will be discussed below.
HOW THE POWER BRAKE SYSTEM OPERATES
The power brake system uses brake fluid stored in a hydraulic accumulator (basically a pressurized reservoir) at pressures around 2500 psi to provide pressurized brake fluid for power braking. An electric pump is used to pressurize the brake fluid. A pressure switch (called a Pressure Warning Switch, or PWS in some Ford manuals) measures the pressure in the accumulator and turns on the pump if pressure gets too low, and turns off the pump when pressure reaches the desired level. The system is designed so the pump runs quite often for brief periods of time the keep the pressure as constant as possible. The pump motor draws around 20 Amps in normal operation. Running this much current through the PWS directly would kill the switch almost instantly, so a relay is used to indirectly power the pump motor. This relay (which Ford refers to as an “anti skid relay” even though it isn’t directly related to the ABS system) is the most common part to fail and cause a loss of power braking and the BRAKE and ABS lights to turn on, but there are other possibilities as well. To avoid throwing parts at the system in hope of fixing it, a relatively simple diagnosis will determine what part has failed.
The figure below shows the various parts of the master cylinder.
Below is a circuit diagram for the pump motor, relay, and the part of the PWS that controls the pump motor.
COMMON PROBLEMS AND SOLUTIONS
Problem: The brake pedal is spongy or the brake pedal goes all the way to the floor, and stopping power is poor.
Solution: If the brake pedal is soft and spongy or goes all the way to the floor, the problem has nothing to do with the electro-hydraulic system (pump motor, pump, PWS, motor relay, wiring). Either there is air in the hydraulic system that will require bleeding the system, or there is a brake fluid leak (leaking caliper, split brake line), or the master cylinder assembly is bad (leaking internal seals, etc). If there are no leaks, and you are sure the system is bled properly, and all the calipers and flex lines are fine (not internally plugged, etc.), then the master cylinder assembly is bad and must be replaced. The master cylinder can not be rebuilt on your workbench, as it requires specialized tools and knowledge, and class 100 clean room conditions.
Problem: Red BRAKE or possibly red BRAKE and yellow ABS lights momentarily come on during hard cornering, acceleration, or braking, but brakes work normally, OR one or both lights on constantly and brakes may or may not seem to work normally.
Solution: The most likely cause here is low brake fluid level in the plastic reservoir. As brake pads wear and caliper pistons more out of the calipers, fluid level can drop slowly over time even if there are no leaks in the system. Of course, leaks will also cause a drop in fluid level.
Check the brake fluid level in the reservoir. This isn’t as easy as it sounds!! The level must be checked with the accumulator completely full (fully charged). If the level isn’t checked with the accumulator full, the level may look OK, but may actually be low. To check the brake fluid level, pump the brake pedal several times with the key off. Turn the key to RUN, and wait until the red BRAKE and yellow ABS lights go off, and the pump motor stops running. Now look at the fluid level and be sure it is at the MAX level indicated on the side of the reservoir.
Problems with the fluid level switch (on top of reservoir) or its wiring harness can cause the lights to come on also. Disconnecting the electrical connector from the fluid level switch will not turn off the lights!
Problem: With the key off, you hear a buzzing sound from the master cylinder area, and the battery drains rapidly causing a no start.
Solution: This one is easy. The pump is running constantly because either the pump relay is stuck on (very likely) or there is a short in the harness (unlikely). Locate the pump motor relay. It is the front relay inside the plastic housing under the vacuum tree that has T/Y, GY/R, GY/Y and PK/LB wires going to it. Pull it out of the plastic housing and remove the relay from its socket. If the pump motor stops running, replace the pump motor relay. If the pump still runs, inspect the heavy gauge T/Y and GY/R wires at the relay socket and harness for missing insulation causing them to short together.
Problem: Loss of power braking (car almost impossible to stop), ABS and BRAKE lights come on, AND the oil pressure, water temperature, and fuel gauges all drop to zero when power brakes are lost and BRAKE and ABS lights come on.
Solution: Another easy one. Replace the ignition switch. Also inspect the ignition switch connector for melting, terminals out of position, etc. If the connector is damaged, replace it.
Problem: The ABS light is on, BRAKE light is off (fluid level is OK) and power braking is normal, but the antilock function doesn’t work.
Solution: Either the ABS power relay hasn’t powered up the ABS computer, or the ABS computer has detected a fault, and disabled the ABS system. Diagnosing the ABS part of the system will not be discussed here.
Problem: The BRAKE light is on, the ABS light is off (fluid level is OK) but power braking is normal.
Solution: The most likely problem here is that the parking brake is on, or there is a problem with the parking brake switch. With parking brake off, disconnect the single connector at the top of the parking brake assembly. If the BRAKE light goes off, replace the parking brake switch. If the BRAKE light is still on, there may be a problem with the fluid level switch, its connector or the harness to the level switch.
Problem: The BRAKE and / or ABS lights briefly come on during braking only (not under cornering, etc.), or briefly come on during repeated hard braking. Braking appears normal or there may brief losses of power braking especially under hard braking.
Solution: The accumulator is likely bad. To test it, turn the key off, pump brake pedal 20 or so times, and turn the key to RUN. BRAKE and ABS lights should be on and the pump motor should be running. The pump motor should run for roughly 30 to 45 seconds, and several seconds before the pump shuts off, the BRAKE and ABS lights should go off. Now, with key still in RUN, apply moderate brake pressure to the pedal and then release. Repeat this until you hear the pump motor start. It should take 2 to 5 brake pedal apply / release cycles of the pedal for the pump to start again, and it should run for several seconds. If these test check out, the accumulator is functioning correctly.
If the initial running time of the pump after pumping the brake pedal 20 times is just a few seconds and if the pump starts to run every time you press the brake pedal, the accumulator is bad, and must be replaced. Note that the accumulator must be 100% depressurized by pumping the brake pedal 40 or so times before removing it!!!!
Problem: The BRAKE light and ABS light are on, the brake pedal is hard, and it is nearly impossible to stop the car.
Solution: The pump isn’t running to pressurize the accumulator. There are several possible causes for this, and it is worth the time to troubleshoot the problem to avoid replacing good parts.
First, we will test the pump motor and its circuitry:
Locate the pump relay in the plastic housing under the vacuum tree. It should be the front relay, having GY/Y, T/Y, GY/R, and PK/LB wires going to the relay socket. Remove the relay from the plastic housing, and remove the relay from its socket. Use a heavy gauge jumper wire to jumper the T/Y and GY/R wires in the socket. The pump motor should run. Do not run the pump for more than 10 seconds! If the pump motor doesn’t run, use a test light (do not use a DMM!) to see if there is 12 V at the T/Y wire. If there isn’t 12 V at the T/Y wire, fuse link S, near the starter solenoid is blown, or the T/Y wire is open somewhere in the harness. If you have power at the T/Y wire but the pump motor doesn’t run with the jumper in the socket, disconnect the pump power connector at the master cylinder (see diagram for pinouts) and jumper the pump motor directly to the battery positive and negative terminals. If the pump motor doesn’t run, the pump motor is bad. Note that there are two positive pins and two negative pins in the connector. This is done to “split up” the high current drawn by the pump. You only need to use one positive and one negative pin for testing purposes.
If the pump motor runs when jumpered directly to the battery, but not when the relay socket is jumpered, the GY/R wire from the relay to the pump connector is open, or the pump ground (GY wire at pump connector) is open or the ground connection is bad. Repair as needed.
If you have a DC amp meter capable of measuring over 25 Amps, you can measure the current draw of the pump motor. Current draw over 24 Amps indicates a problem with the pump motor, such as partly seized motor bearings, or shorted motor windings. If current draw exceeds 24 Amps, the motor should be replaced.
Now that we have verified the pump motor and its circuitry are working, we will turn to the pump motor control circuitry:
The pump motor is powered up by the pump motor relay. The relay is turned on and off by one set of contacts in the PWS. If the pump motor relay is in its socket, remove the relay from its socket. Connect a test light between the GY/Y wire in the relay socket and a good ground. Turning the key to RUN should light up the test light. If the light doesn’t light up, suspect the ignition switch or harness. If this checks out, put the relay back in its socket. Now, remove the 5 pin connector from the PWS. The diagram shows pinouts for the PWS connector. With the key in run, jumper pins one and four in the connector. The pump motor relay should click, and the pump should run. If you hear the relay click but the pump doesn’t run, replace the relay. Do not run the pump for more than 10 seconds! If the pump motor runs, replace the PWS. Note that the accumulator must be 100% depressurized by pumping the brake pedal 40 or so times before removing the PWS!!!! (Note that one NATO member that had a bad PWS cut the “top” end off the switch, pulled out the connector, and found a damaged ribbon cable going to the connector, was able to repair it, and JB Weld the PWS back together. Try this at your own risk.)
If the pump motor doesn’t run / relay doesn’t click with pins one and four in the PWS jumpered, run a jumper from pin four of the PWS to a good ground. If the relay clicks and motor runs, repair the circuit from pin one of the PWS connector to ground. If you hear the relay click but the pump doesn’t run, replace the relay.
As a final test, remove the pump motor relay from its socket, and attach a test light between the GY/Y and PK/LB wires in the relay socket. Jumper pins one and four in the PWS connector. If the test light lights up, replace the relay. If the light doesn’t light up with pins one and four in the PWS jumpered, run a jumper from pin four of the PWS to a good ground. If the test light lights up, repair the circuit from pin one of the PWS connector to ground. If the test light does light up when pins one and four are jumpered and the key is in RUN, but the relay doesn’t click / pump doesn’t run when pins one and four are jumpered and the key is in RUN, replace the pump motor relay.