Cruise Control Inoperative LG5
Diagnostic Aids
Important: Perform the following in order to avoid misdiagnosis.
| • | Inspect for proper operation of brake lamps. |
| • | Inspect for stored Diagnostic Trouble Codes (DTCs) in the PCM. Refer to Powertrain OBD System check in Engine Controls. |
| • | EMI on the speed sensor signal circuit may cause erratic cruise control operation. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Does the test lamp light? | -- | ||
2 |
Does the DMM indicate continuity? | -- | ||
3 | Connect a DMM to each end of CKT 84 (DK BLU). Does the DMM indicate continuity? | -- | ||
4 | Connect a DMM to each end of CKT 87 (GRY/BLK). Does the DMM indicate continuity? | -- | ||
5 |
Does the DMM indicate continuity? | -- | ||
6 |
Does the DMM indicate continuity? | -- | ||
7 |
Does the DMM indicate continuity? | -- | ||
8 | Connect a DMM from CKT 808 (BLK) to ground at the cruise control switch harness connector. Does the DMM indicate continuity? | -- | ||
9 | Replace the cruise control switch. Is the cruise control operative? | -- | System OK | -- |
10 | Repair the stoplamps switch control circuit. Refer to Wiring Repairs in Wiring Systems. Is the cruise control operative? | -- | System OK | -- |
11 | Repair CKT 397 (GRY). Refer to Wiring Repairs in Wiring Systems. Is the cruise control operative? | -- | System OK | -- |
12 | Repair CKT 84 (DK BLU). Refer to Wiring Repairs in Wiring Systems. Is the cruise control operative? | -- | System OK | -- |
13 | Repair CKT 87 (GRY/BLK). Refer to Wiring Repairs in Wiring Systems. Is the cruise control operative? | -- | System OK | -- |
14 | Repair CKT 808 (BLK). Refer to Wiring Repairs in Wiring Systems. Is the cruise control operative? | -- | System OK | -- |
15 | Reconnect all previously disconnected components and refer to the Cat® Diesel Truck Engine Service Manual-3126 HUEI for further diagnosis of the cruise control system. Does the cruise control system operate properly? | -- | System OK | -- |
Cruise Control Inoperative L21/LP4
Diagnostic Aids
Important: Perform the following in order to avoid misdiagnosis.
| • | Inspect for proper operation of brake lamps. |
| • | Inspect for stored Diagnostic Trouble Codes (DTCs) in the PCM. Refer to Powertrain OBD System check in Engine Controls. |
| • | EMI on the speed sensor signal circuit may cause erratic cruise control operation. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Cruise Control Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Did both inputs respond? | -- | Go to Step 3 | Go to Step 6 |
3 | Turn the cruise control switch ON while monitoring the scan tool. Did the input respond? | -- | Go to Step 4 | Go to Step 8 |
4 | Move the on/off switch to the R/A (resume/accelerate) position and press the SET/COAST switch while monitoring the scan tool. Did both the inputs respond? | -- | Go to Step 5 | Go to Step 8 |
5 |
Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 12 |
6 |
Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 7 |
7 | Probe the stoplamps switch C2 circuit with a test lamp that is connected to system voltage. Does the test lamp illuminate? | B+ | Go to Step 14 | Go to Step 11 |
8 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 19 |
9 |
Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 15 |
10 | Test the brake switch circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 17 |
11 | Test the brake switch circuit for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 17 |
12 | Probe the clutch circuit with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 21 | Go to Step 13 |
13 | Test the clutch circuit for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 16 |
14 | Inspect for poor connections at the harness connector of the stoplamps switch interface module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 18 |
15 | Inspect for poor connections at the harness connector of the TAC module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 20 |
16 | Replace the clutch switch. Did you complete the replacement? | -- | Go to Step 21 | -- |
17 | Replace the stoplamps switch. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes or Stop Lamp Switch Replacement in Air Brakes. Did you complete the replacement? | -- | Go to Step 21 | -- |
18 | Replace the stoplamps switch interface module. Did you complete the replacement? | -- | Go to Step 21 | -- |
19 | Replace the cruise control switch. Refer to Multifunction Turn Signal Lever Replacement - On Vehicle in Steering Wheel and Column - Tilt. Did you complete the replacement? | -- | Go to Step 21 | -- |
20 | Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement in Engine Controls - 7.4L. Did you complete the replacement? | -- | Go to Step 21 | -- |
21 | Operate the vehicle within the conditions for cruise control operation. Does the cruise control system operate correctly? | -- | System OK | Go to Step 2 |
