Circuit Description
The differential lock system is electric/air operated. This circuit will only diagnose the electrical portion of the system and assumes the air operated portion is operating normally, mechanically. With the differential lock switch turned on, voltage is applied to the differential lock control valve. The differential lock control valve then opens supplying air pressure to engage the lockout.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests for an intermittent condition.
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This step tests for proper voltage present at the differential lock switch.
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This step tests the differential lock switch for proper operation.
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This step tests the differential lock solenoid valve feed circuit.
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This step tests the ground circuit.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Differential Lock Schematics | ||||
1 | Did you review the Differential Lock Description and Operation and perform the necessary inspections? | -- | Go to Step 2 | |
Verify the fault is present. Does the system operate normally? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 4 | Go to Step 7 | |
Test for continuity across the differential lock switch with the switch pressed. Is continuity present? | -- | Go to Step 5 | Go to Step 8 | |
Does the voltage measure within the specified value? | 9-14 V | Go to Step 6 | Go to Step 9 | |
Connect a test lamp from the differential lock solenoid valve feed circuit to the ground circuit. Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 10 | |
7 | Repair an open in the ignition 3-voltage circuit. Refer to Circuit Testing and Wiring Repairs. Did you complete the repair? | -- | Go to Step 12 | -- |
8 | Replace the differential lock switch. Refer to Differential Lock Switch Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
9 | Repair an open in the differential lock solenoid valve feed circuit. Refer to Circuit Testing and Wiring Repairs. Did you complete the repair? | -- | Go to Step 12 | -- |
10 | Repair an open in the ground circuit. Refer to Circuit Testing and Wiring Repairs. Did you complete the repair? | -- | Go to Step 12 | -- |
11 | Replace the differential lock Control Valve. Refer to Inter-Axle Differential Lock Control Valve Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 | Operate the vehicle within the conditions for causing the symptom as specified in the supporting text. Does the system operate normally? | -- | System OK | Go to Step 2 |
