Circuit Description
The powertrain control module (PCM) determines operation of the two speed engine cooling fans based on A/C request, engine coolant temperature, and vehicle speed. The engine cooling fan 1 low speed relay is energized by the body control module (BCM). When the PCM determines that the engine cooling fan 1 relay should be enabled, the PCM will send a message on the Class II serial data circuit to the powertrain interface module (PIM). The PIM will then convert the PCM Class II message to a UART message and supply this UART message to the BCM. This PCM message will request the BCM to supply the needed ground signal for the engine cooling fan 1 relay to operate. After the BCM provides the ground signal for the engine cooling fan 1 relay, the BCM will send a message back to the PIM confirming that the ground signal was commanded. The PIM will convert this message from the BCM to Class II and supply to the PCM. If the PCM does not receive a response back from the BCM DTC U1067 will set.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The PIM sends a Low Speed request signal to the BCM, and there is no acknowledgment back from the BCM.
Action Taken When the DTC Sets
The PCM will not illuminate the malfunction indicator lamp (MIL).
Conditions for Clearing the MIL/DTC
| • | A Last Test Failed (current DTC) clears, after the ignition has been cycled and the PIM receives a low speed fan response from the BCM. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | A faulty connection at the PCM, inspect the harness connectors for the following conditions. |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Faulty terminal to wire connections |
| • | Inspect the wiring harness for damage. |
Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This test is determines if any BCM DTCs may be set. There may be a BCM DTC that is related to this circuit, and diagnosing this BCM DTC first may resolve the fault.
-
An open or short to ground on the UART serial data circuit will disable any communication between the PIM and BCM. This will cause DTC U1064 to set. This DTC should be diagnosed first.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views | |||
1 | Did you perform the Engine Cooling Diagnostic System Check? | Go to Step 2 | |
Install a scan tool. Are there any body control module (BCM) DTCs set? | Go to Diagnostic Trouble Code (DTC) List in Body Control System | Go to Step 3 | |
Is PIM DTC U1064 set? | Go to Diagnostic Trouble Code (DTC) List in Data Link Communications | Go to Step 4 | |
4 |
Does the low speed cooling fan operate when commanded ON, using the Tech 2? | Go to Step 5 | |
5 |
Does the BCM Low Fan Relay parameter change from OFF to ON when the cooling fans operate? | Go to Diagnostic Starting Point - Body Control System in Body Control System | Go to Step 6 |
6 | Inspect for poor connections at the harness connector of the powertrain interface module (PIM). 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 8 | Go to Step 7 |
7 | Replace the PIM. Refer to: Powertrain Interface Module Replacement in Body Control System. Did you complete the replacement? | Go to Step 8 | -- |
8 |
Does the DTC reset? | Go to Step 2 | System OK |
