Test 4A

Test 4A: Repairing -- Pump/Motor Circuits:

System Relay Circuits Schematics:

NOTE: You must perform Test 1A, before proceeding with this test.

PUMP/MOTOR CIRCUIT

When Its Monitored
It's monitored continuously and can be set by the following conditions. The pump/motor voltage is tested every three seconds (voltage should be low) before drive-off occurs and any time while not in Antilock Brake System (ABS) cycling mode. While in cycling mode, the pump/motor is again tested every 200 milliseconds (voltage should be high).

Possible Causes:
^ Open fused B+ circuit to the ABS pump/motor relay
^ Motor circuit open
^ CAB failed
^ Open ABS pump/motor relay output circuit
^ Open ABS pump/motor relay control circuit
^ ABS pump/motor relay output circuit shorted to B+
^ Failed relay box
^ Relay box not connected to the hydraulic control unit

PUMP/MOTOR MONITOR CIRCUIT

When Its Monitored
The test is conducted on a continual basis when the pump/motor should be off. The following could set the condition. The pump/motor relay supplies power to the pump/motor located in the Hydraulic Control Unit (HCU). It is controlled by the Controller Antilock Brake (CAB) through cavity 16. The relay output voltage is monitored by the CAB at cavity 20. When the pump is off, the monitor line should be pulled low through the pump/motor windings to ground. When the pump is on the monitor line should be high. The trouble code is stored if voltage of the monitor line (cavity 20) is above 6 volts for 3 seconds when the motor is commanded off.

Possible Causes:
^ Open pump/motor windings
^ Open pump/motor output circuit to CAB cavity 20
^ Open pump/motor ground circuit
^ Pump/motor relay output circuit shorted to B+
^ Loose or corroded connector terminals
^ Relay box not connected to the HCU
^ Pump/motor relay control circuit shorted to ground
^ Failed relay box

PUMP/MOTOR RELAY OUTPUT CIRCUIT

When Its Monitored
The test is conducted on a continual basis when the pump/motor should be on. The following could set the condition. The pump/motor relay supplies power to the pump/motor located in the HCU. It is controlled by the by the CAB through cavity 16. The relay output voltage is monitored by the CAB at cavity 20. When the pump is off, the monitor line should be pulled low through the pump/motor windings to ground. When the pump is on the monitor line should be high. The trouble code is stored if voltage of the monitor line (cavity 20) is below 7 volts for 200 milliseconds when the motor is commanded on for normal cycling or 100 milliseconds during drive off test.

Possible Causes:
^ Open pump/motor relay output circuit to pump
^ Open pump/motor fuse in power distribution center
^ Pump/motor relay output circuit is shorted to ground
^ Loose or corroded connector terminals
^ Open fused B+ circuit to relay
^ Pump/motor seized
^ Failed relay box

INACTIVE TROUBLE CODE CONDITION
You have just attempted to simulate the condition that initially set the trouble code message. The following additional checks may assist you in identifying a possible intermittent problem:

^ Visually inspect related wire harness connectors. Look for broken, bent, pushed out, or corroded terminals.

^ Visually inspect the related harnesses. Look for chafed, pierced, or partially broken wire.

^ Refer to any hotlines or technical service bulletins that may apply.