Diagnostic Aids
Important: Perform the following in order to avoid misdiagnosis:
| • | Inspect for proper adjustment of the brake switches . |
| • | Inspect for proper operation of brake lamps. |
| • | Inspect throttle linkage for mechanical binding which could cause the system to malfunction. |
| • | Inspect cruise control cable adjustment, should have minimum slack. |
| • | Inspect for stored Diagnostic Trouble Codes (DTCs) in the PCM. Refer to Diagnostic System Check - Engine Controls in Engine Controls-3.8L. |
| • | EMI on the speed sensor signal circuit may cause erratic cruise control operation. |
Conditions for Enabling Cruise Control
| • | When vehicle speed is more than 40 km/h (25 mph). |
| • | When PARK, REVERSE, NEUTRAL, or 1st gear is not indicated. |
| • | When an over/undercharged battery condition does not exist. |
| • | With normal engine RPM. |
| • | Without high engine RPM. e.g. fuel cut-off. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Cruise Control Schematics | ||||
1 | Did you perform the Cruise Control Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the test lamp illuminate? | -- | Go to Step 3 | Go to Step 34 |
3 | Probe the ignition 3 voltage circuit of the cruise control module with a test lamp that is connected to the ground circuit of the cruise control module. Does the test lamp illuminate? | -- | Go to Step 4 | Go to Step 35 |
4 |
Does the test lamp illuminate on any of the circuits? | -- | Go to Step 16 | Go to Step 5 |
5 |
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 17 |
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 19 |
7 |
Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 20 |
8 | Probe the TCC brake switch circuit with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 21 |
9 | Press the brake pedal while monitoring the test lamp. Does the test lamp illuminate? | -- | Go to Step 24 | Go to Step 10 |
10 | Probe the stoplamp supply voltage circuit with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 22 | Go to Step 11 |
11 | Press the brake pedal while monitoring the test lamp. Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 26 |
12 | Probe the cruise inhibit signal circuit with a test lamp that is connected to B+. Does the test lamp illuminate? | -- | Go to Step 27 | Go to Step 13 |
13 | Use a scan tool in order to command the cruise inhibit OFF. Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 28 |
14 | Probe the cruise engaged signal circuit with a DMM that is connected to a good ground. Does the voltage measure near the specified value? | B+ | Go to Step 15 | Go to Step 29 |
15 | Check the speedometer for proper operation. Does the speedometer operate properly? | -- | Go to Step 30 | |
16 | Test the signal circuit that illuminated the test lamp 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 43 | Go to Step 34 |
17 | Test the cruise on switch signal 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 43 | Go to Step 18 |
18 | Test the ignition 3 voltage circuit of the cruise control switch for an open or high resistance and the cruise control Set/Coast switch, Resume/Accelerate switch signal circuits for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 34 |
19 | Test the cruise control set/coast switch signal 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 43 | Go to Step 34 |
20 | Test the cruise control resume/accelerate switch signal 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 43 | Go to Step 34 |
21 | Check the stoplamp switch for proper adjustment. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 23 |
22 | Check the ABS/TCC switch for proper adjustment. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 25 |
23 | Test the TCC brake switch signal 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 43 | Go to Step 31 |
24 | Test the TCC brake switch signal 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 43 | Go to Step 31 |
25 | Test the stoplamp supply voltage 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 43 | Go to Step 32 |
26 | Test the stoplamp switch supply 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 43 | Go to Step 32 |
27 | Test the cruise control inhibit signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 33 |
28 | Test the cruise control inhibit circuit for an open, a high resistance, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 33 |
29 | Test the cruise control engaged signal circuit for an open, a high resistance, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 33 |
30 | Test the speed sensor circuit for an open or a high resistance between the cruise control module and PCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 43 | Go to Step 35 |
31 | Inspect for poor connections at the harness connector of the ABS/TCC switch. 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 43 | Go to Step 38 |
32 | Inspect for poor connections at the harness connector of the stoplamp switch. 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 43 | Go to Step 39 |
33 | Inspect for poor connections at the harness connector of the PCM. 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 43 | Go to Step 40 |
34 | Inspect for poor connections at the harness connector of the cruise control switch. 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 43 | Go to Step 41 |
35 | Inspect for poor connections at the harness connector of the cruise control 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 43 | Go to Step 42 |
36 | Repair the ignition 3 voltage circuit of the cruise control module. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 43 | -- |
37 | Repair the ground circuit of the cruise control module. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 43 | -- |
38 | Replace the ABS/TCC switch. Refer to Stop Lamp Switch Replacement . Did you complete the replacement? | -- | Go to Step 43 | -- |
39 | Replace the stoplamp switch. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes. Did you complete the replacement? | -- | Go to Step 43 | -- |
40 |
Important: The replacement PCM must be reprogrammed. Refer to Powertrain Control Module Programming in Engine Controls-3.8L. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls-3.8L. Did you complete the replacement? | -- | Go to Step 43 | -- |
41 | Replace the multifunction turn signal lever . Refer to Multifunction, Turn Signal, and Hazard Switch Replacement - On Vehicle in Steering Wheel and Column. Did you complete the replacement? | -- | Go to Step 43 | -- |
42 | Replace the cruise control module. Refer to Cruise Control Module Replacement . Did you complete the replacement? | -- | Go to Step 43 | -- |
43 | Operate the vehicle within the conditions for cruise control operation. Does the cruise control system operate correctly? | -- | System OK | Go to Step 2 |
