Circuit Description
The instrument panel module (IPM) sends cruise control data to the engine control module (ECM). The data is sent to the ECM through a communication network called the GM local area network (LAN). Two circuits are used to communicate LAN data between the ECM and IPM. A fault in the LAN will not cause DTC U0423 to set by itself. If a LAN fault occurs, other DTCs will set in addition to DTC U0423.
If the ECM receives invalid cruise control data from the IPM, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC U0423 IPM Communication Circuit Performance
Conditions for Running the DTC
| • | The ignition is on for more than 3 seconds. |
| • | The ignition 1 voltage is between 10.5-18 volts. |
| • | No other communication errors are present. |
| • | DTC U0423 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM receives no valid cruise control data from the IPM for more than 1 second.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Component Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 |
Note: Record all Failure Records before clearing the DTC. Using Clear Info erases the Failure Records from the engine control module (ECM). Did you record any Freeze Frame/Failure Records for a DTC other than U0423? | Go to Step 3 | |
3 |
Did DTC U0423 fail this ignition? | Go to Step 4 | Go to Intermittent Conditions |
4 | Did an instrument panel module (IPM) DTC, a cruise control related DTC, or any other "U" DTC also set? | Go to Step 5 | |
5 | Test the LAN circuits in the wiring harness between IPM and the ECM for a high resistance or for a poor connection at the module connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | Go to Step 7 | Go to Step 6 |
6 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 7 | -- |
7 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 7 |
8 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
