High Idle Switch Diagnosis with RPO UF3
Circuit Description
The high idle system is used to provide additional engine power when needed for vehicle accessories. The engine control module (ECM) controls the high idle operation based on various sensor inputs and the high idle switch on the instrument console.
Diagnostic Aids
If the high idle system is inoperative but the switch circuit works, inspect for the following conditions:
| • | The high idle switch option is not programmed--Refer to High Idle Switch Programming . |
| • | There are DTCs set--Diagnose these first. |
| • | There is a non-DTC fault in one of the following components or systems: |
| - | The brake switch |
| - | The clutch switch |
| - | The vehicle speed sensor |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 |
Does the high idle switch parameter change state? | Go to Diagnostic Aids | Go to Step 3 |
3 | Does the high idle switch parameter indicate ON all the time? | Go to Step 4 | Go to Step 6 |
4 |
Does the high idle switch indicate OFF? | Go to Step 13 | Go to Step 5 |
5 |
Does the test lamp illuminate? | Go to Step 11 | Go to Step 14 |
6 |
Does the high idle switch indicate ON? | Go to Step 7 | Go to Step 8 |
7 | Probe the ground circuit of the high idle switch with a test lamp connected to battery voltage. Does the test lamp illuminate? | Go to Step 9 | Go to Step 12 |
8 | Test the high idle signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 15 | Go to Step 10 |
9 | Test for an intermittent and for a poor connection at the high idle switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 15 | Go to Step 13 |
10 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 15 | Go to Step 14 |
11 | Repair the short to ground in the high idle switch signal circuit. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 15 | -- |
12 | Repair the open or high resistance in the ground circuit of the high idle switch . Refer to Wiring Repairs . Did you complete the repair? | Go to Step 15 | -- |
13 | Replace the high idle switch. Did you complete the replacement? | Go to Step 15 | -- |
14 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 15 | -- |
15 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
