Page 1185 of 4284
Symptom:
SYSTEM OVERVOLTAGE
When Monitored and Set Condition:
SYSTEM OVERVOLTAGE
When Monitored: Ignition on. The CAB monitors the Fused B(+) circuit at all times for
proper system voltage.
Set Condition: If the voltage is above 16.5 volts for greater than 420 milliseconds (ms),
the Diagnostic Trouble Code (DTC) is set.
POSSIBLE CAUSES
BATTERY OVERCHARGED
FUSED IGNITION SWITCH OUTPUT HIGH
GROUND CIRCUIT OPEN
CAB - INTERNAL FAULT
INTERMITTENT DTC
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, erase DTC's.
Turn the ignition off.
Turn the ignition on.
Start the engine.
With the DRBIIIt, read DTC's.
Does the DRBIIItdisplay System Overvoltage DTC?All
Ye s®Go To 2
No®Go To 6
2 Turn the ignition off.
Inspect for battery charger connected to battery.
Is a battery charger connected to the battery?All
Ye s®Charge battery to proper level. Disconnect the battery charger.
Clear DTC's.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 3
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BRAKES (CAB)
Page 1186 of 4284

TEST ACTION APPLICABILITY
3 Turn the ignition off.
Disconnect the CAB connector.
Note: Check connector - Clean/repair as necessary.
Start the engine.
Raise engine speed above 1,800 RPM.
Measure the battery voltage.
Is the voltage above 16.5 volts ?All
Ye s®Refer to appropriate service information for charging system
testing and repair.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 4
4 Turn the ignition off.
Disconnect the CAB connector.
Note: Check connector - Clean/repair as necessary.
Measure the resistance of the ground circuits.
Is the resistance below 1.0 ohm?All
Ye s®Go To 5
No®Repair the Ground circuit for an open.
Perform ABS VERIFICATION TEST - VER 1.
5 If there are no potential causes remaining, view repair. All
Repair
Replace the Controller Antilock Brake.
Perform ABS VERIFICATION TEST - VER 1.
6 Turn the ignition off.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wire harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Refer to any Hotline letters or Technical Service Bulletins that may apply.
Were any problems found?All
Ye s®Repair as necessary.
Perform ABS VERIFICATION TEST - VER 1.
No®Test Complete.
29
BRAKES (CAB)
SYSTEM OVERVOLTAGE ÐContinued
Page 1187 of 4284

Symptom:
SYSTEM UNDERVOLTAGE
When Monitored and Set Condition:
SYSTEM UNDERVOLTAGE
When Monitored: Ignition on. The CAB monitors the Fused Ignition Switch Output
circuit voltage above 10 km/h (6 mph) every 7 milliseconds for proper system voltage.
Set Condition: If the voltage is below 9.5 volts, the Diagnostic Trouble Code (DTC) is set.
POSSIBLE CAUSES
BATTERY VOLTAGE LOW
INTERMITTENT DTC
FUSED IGNITION SWITCH OUTPUT CIRCUIT HIGH RESISTANCE
CAB - INTERNAL FAULT
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, erase DTC's.
Turn the ignition off.
Turn the ignition on.
Start the engine.
Drive the vehicle above 16 km/h (10 mph) for at least 20 seconds.
Stop the vehicle
With the DRBIIIt, read DTC's.
Does the DRBIIItdisplay System Undervoltage DTC?All
Ye s®Go To 2
No®Go To 5
2 Engine Running.
Measure the battery voltage.
Is the battery voltage below 10 volts?All
Ye s®Refer to appropriate service information for charging system
testing and repair.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 3
3 Disconnect the CAB harness connector.
Turn the ignition on.
Measure the voltage of the Fused Ignition Switch circuit.
Is the voltage above 10 volts?All
Ye s®Go To 4
No®Repair the Fused Ignition Switch Output Circuit for high resis-
tance
Perform ABS VERIFICATION TEST - VER 1.
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BRAKES (CAB)
Page 1188 of 4284
TEST ACTION APPLICABILITY
4 If there are no potential causes remaining, view repair. All
Repair
Replace the Controller Antilock Brake.
Perform ABS VERIFICATION TEST - VER 1.
5 Turn the ignition off.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wire harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Refer to any Hotline letters or Technical Service Bulletins that may apply.
Were any problems found?All
Ye s®Repair as necessary.
Perform ABS VERIFICATION TEST - VER 1.
No®Test Complete.
31
BRAKES (CAB)
SYSTEM UNDERVOLTAGE ÐContinued
Page 1189 of 4284

Symptom:
VALVE POWER FEED FAILURE
When Monitored and Set Condition:
VALVE POWER FEED FAILURE
When Monitored: Ignition ON for at least 3.5 seconds. ABS Power Relay closed. Valve
command for a particular solenoid not present.
Set Condition: Low feedback voltage from the low side of all the solenoids for over 20
consecutive controller checks spaced 5 ms apart.
POSSIBLE CAUSES
INTERMITTENT DTC
BLOWN FUSE - FUSED B(+) CIRCUIT
NO B+ SUPPLY TO FUSE
FUSED B(+) CIRCUIT OPEN
B(+) CIRCUIT SHORTED TO GROUND
CAB - FUSED B(+) CIRCUIT OPEN
CAB - FUSED B(+) CIRCUIT SHORTED TO GROUND
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, erase DTC's.
Turn the ignition off.
Turn the ignition on.
Drive the vehicle above 25 km/h (15 mph) for at least 10 seconds.
Stop the vehicle.
With the DRBIIIt, read DTC's.
Does the DRBIIItdisplay Valve Power Feed Circuit DTC present right now?All
Ye s®Go To 2
No®Go To 9
2 Turn the ignition off.
Remove and Inspect the ABS Fuse 21 in the IPM.
Is the Fuse blown?All
Ye s®Go To 3
No®Go To 6
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BRAKES (CAB)
Page 1190 of 4284

TEST ACTION APPLICABILITY
3 Turn the ignition off.
Remove the ABS Fuse 21 from the IPM.
Disconnect the CAB harness connector.
Note: Check connector - Clean/repair as necessary.
Using a test light connected to 12 volts, probe the Fused B(+) Circuit.
Does the test light illuminate brightly?All
Ye s®Repair the Fused B(+) Circuit short to ground.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 4
4 Turn the ignition off.
Remove the ABS Fuse 21 from the IPM.
The CAB must be connected for the results of this test to be valid.
Using a test light connected to 12 volts, probe the Fused B(+) Circuit at the IPM fuse
terminal.
Does the test light illuminate brightly?All
Ye s®Replace the Controller Antilock Brake in accordance with the
Service Information.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 5
5 Turn the ignition off.
If there are no potential causes remaining, view repair.All
Continue
Replace the Fuse.
Perform ABS VERIFICATION TEST - VER 1.
6 Remove the ABS Fuse 21 from the IPM.
Turn the ignition on.
Measure the voltage of the Fused B+ supply to Fuse 21 in the IPM.
Is the voltage above 10 volts?All
Ye s®Go To 7
No®Repair the B+ Supply circuit for an open.
Perform ABS VERIFICATION TEST - VER 1.
7 Turn the ignition off.
Remove the ABS Fuse 21 from the IPM.
Disconnect the CAB harness connector.
Note: Check connector - Clean/repair as necessary.
Measure the resistance of the Fused B(+) circuit between IPM Fuse terminal 21 and
the CAB connector.
Is the resistance below 5 ohms?All
Ye s®Go To 8
No®Repair the Fuse B+ circuit for an open.
Perform ABS VERIFICATION TEST - VER 1.
8 If there are no possible causes remaining, view repair. All
Repair
Replace the Controller Antilock Brake in accordance with the
Service Information.
Perform ABS VERIFICATION TEST - VER 1.
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BRAKES (CAB)
VALVE POWER FEED FAILURE ÐContinued
Page 1191 of 4284
TEST ACTION APPLICABILITY
9 Turn the ignition off.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wire harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Refer to any Hotline letters or Technical Service Bulletins that may apply.
Were any problems found?All
Ye s®Repair as necessary.
Perform ABS VERIFICATION TEST - VER 1.
No®Test Complete.
34
BRAKES (CAB)
VALVE POWER FEED FAILURE ÐContinued
Page 1192 of 4284

Symptom:
*BRAKE LAMP SWITCH
POSSIBLE CAUSES
CHECK BRAKE LAMP SWITCH OUTPUT
BRAKE LAMP SWITCH B+ OPEN
BRAKE LAMP SWITCH OUTPUT CIRCUIT SHORT OR OPEN
BRAKE LAMP SWITCH OPEN
CAB -- INTERNAL OPEN
TEST ACTION APPLICABILITY
1 With the DRBIIItin Inputs/Outputs, read the Brake Lamp Switch state.
Press and release the brake pedal.
Does the DRBIIItdisplay PRESSED and RELEASED?All
Ye s®The Brake Lamp Switch is OK.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 2
2 Disconnect the Brake Lamp Switch harness connector.
Using a 12-volt test light connected to ground, check the Brake Lamp Switch Fused
B+ circuit.
Does the test light illuminate brightly ?All
Ye s®Go To 3
No®Repair the Brake Lamp Switch Fused B+ circuit for an open.
Perform ABS VERIFICATION TEST - VER 1.
3 Disconnect the Brake Lamp Switch harness connector.
Connect a jumper wire between the Brake Lamp Switch B+ and Output circuits.
With the DRBIIItin Inputs/Outputs, read the Brake Lamp Switch state.
Does the DRBIIItdisplay PRESSED?All
Ye s®Replace the Brake Lamp Switch in accordance with the Service
Information.
Perform ABS VERIFICATION TEST - VER 1.
No®Go To 4
4 Disconnect the CAB harness connector.
Disconnect the Brake Lamp Switch harness connector.
Check the Brake Lamp Switch Output circuit for a short to voltage and an open.
Is the Brake Lamp Switch Output circuit shorted or open?All
Ye s®Repair the Brake Lamp Switch Output circuit for a short to
voltage or an open.
Perform ABS VERIFICATION TEST - VER 1.
No®Replace the Controller Anti-Lock Brake in accordance with the
Service Information.
Perform ABS VERIFICATION TEST - VER 1.
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BRAKES (CAB)