Corrective Action Steps 1 Thru 4
CORRECTIVE ACTION STEPSSTEP # 1 - LOW FLUID IN BOOSTER PUMP RESERVOIR DUE TO EXTERNAL LEAK.
A. Make ten medium to high effort brake applies with ignition off to de-pressurize the system. Check fluid level in booster pump reservoir by observing if level falls between the two gauge marks located on the inside of the pump reservoir (Figure 2).
NOTE:
If pressure switch has a black plastic body, the unit must be refitted with the updated pressure switch which has a gray plastic body (P/N 18018141).
B. Inspect the pressure switch and adjacent areas for external leaks. This may require wiping those areas dry and observing for fluid leakage during and after the pump motor run time. If fluid is observed, replace appropriate component.
C. With unit removed from vehicle, check for leakage at rear. Rubber boot should not have excess amounts of fluid inside. If fluid is observed, repair Powermaster with Seal Repair Kit 18020067.
D. Bleed and refill unit to proper gauge level in reservoir with system in the de-pressurized state.
STEP # 2: ACCUMULATOR OPERATION TEST: PUMP RUNS MORE THAN 8 SECONDS
A. Check for internal leakage in diagnostics procedure. If pump does not self-cycle within five minutes, proceed to Step C.
B. If pump self-cycles (ignition "on", no brakes applied), an internal pressure leak is present.
1. Place a short piece (6-12 inches) of flexible plastic tubing (approximately 1/4 inch-1/2 inch diameter) over Port A in the inboard pump reservoir (Figure 2). If leakage is occurring, fluid will rise in the tube. Repair this fault with Seal Repair Kit 18020067. If no leakage is found, examine Port B.
2. Place the same plastic tubing over Port B (Figure 2). If leakage is observed here, repair with Check Valve Repair Kit 18018552.
C. De-pressurize the system with ten brake applies and ignition off. Fluid level must be within gauge marks in reservoir.
D. Install J35126 tool and test to determine if fault is in motor and pump assembly or if fault is in the accumulator. (See NOTE BELOW.)
E. Turn ignition on. Wait until pump motor shuts off. Turn ignition off. Slowly bleed off the accumulator pressure with J35126 bleed valve - returning fluid to the pump reservoir (inboard side, Figure 2). The gauge pressure will suddenly drop to zero at the accumulator gas pre-charge point.
1. If the drop-off point occurs below 200 psi, replace the accumulator (P/N 18014978 or 18018722).
2. If the drop-off point occurs above 200 psi, replace the pump and motor assembly (P/N 18011279).
NOTE:
J35126 per Step 2.D. above is the preferred method. However, if such a tool is not available, the alternative method listed below will provide the necessary diagnostic information to determine the fault.
1. De-pressurize the system per 2.C. Turn ignition on and check the time from motor start running to motor stop running.
2. If time to motor shut-off is less than 15 seconds, replace the accumulator.
3. If the time to motor shut-off is more than 15 seconds, replace motor and pump assembly and then retest accumulator per Accumulator Operation Test (Step # 2 above). If run time on that test is still greater than 8 seconds, also replace the accumulator.
STEP # 3: BOOSTER PUMP MOTOR DOES NOT RUN
Confirm that the 30 amp brake system fuse is not defective, otherwise replace. Next, disconnect the pressure switch and pump motor electrical connectors and conduct the following electrical circuit checks:
A. Pressure Switch (Ohmmeter Test)
1. De-pressurize system by pumping brake pedal at least ten times with ignition switch off.
2. Using suitable ohmmeter, all terminals should have continuity with each other. If not, switch must be replaced.
B. Booster Motor (Ohmmeter Test)
1. Meter should show resistance between motor terminals "B" and "D".
2. Meter should indicate open circuit between motor terminals "A" and "C".
3. Replace motor and pump assembly if above conditions are not met.
C. Pressure Switch Connector and Harness (Volt-Ohmmeter Test)
1. Make sure parking brake is released.
2. With ignition on, using a suitable ohmmeter, pressure switch terminal "A" should show continuity with motor terminal "D".
3. With ignition on, using a suitable voltmeter, pressure switch terminal "B" should be 12 volts relative to vehicle chassis ground.
4. If voltage at pressure switch terminal "B" is low or zero, disconnect electrical connector from combination valve. If voltage at "B" is now normal, combination valve wire harness or switch is at fault. If voltage at terminal "B" remains low or zero, red brake warning light circuit is defective.
5. If any of the above tests fail, wire harness and electrical connections must be replaced or repaired.
D. Pump Motor Connector and Harness (Volt-Ohmmeter Test)
1. With ignition on, using suitable ohmmeter, motor terminal "A" should show continuity with vehicle chassis ground.
2. With ignition on, using suitable voltmeter, motor terminal "B" should show 12 volts relative to chassis ground.
3. With ignition on, using suitable voltmeter, motor terminal "C" should show 12 volts relative to chassis ground.
NOTE: This is the main electrical supply to the motor. If voltage is not present, check the 30 amp brake system fuse.
4. Recheck terminal "D" as per Step 3.C.1 above.
5. If any of the above tests fail, wire harness and electrical connections must be replaced or repaired.
STEP # 4: MOTOR DOES NOT TURN OFF WITHIN 15 SECONDS (IGNITION "ON")
A. Check fluid level per Step 1.A.
B. Install J35126 Tool per Step 2.D. and test to determine if fault is in motor and pump assembly, pressure switch, or internal booster leakage.
C. Turn ignition on. Wait 20 seconds. Monitor booster pressure on J35126 gauge.
1. If pressure exceeds 770 psi, replace pressure switch.
2. If pressure does not reach the 540 psi - 770 psi pump shutoff range, check Port A and Port B in the booster pump reservoir (Figure 2) per Step 2.B. above. If fluid is flowing in either port, the booster is leaking internally. Repair unit with Seal Repair Kit 18020067. If fluid is not flowing in either port, the motor and pump assembly is defective (unable to provide the required pressure) and should be replaced.