DIAGNOSTIC CODE INDEX
| DTC | Description |
|---|---|
| DTC P0480 or P0481 | High Speed or Low Speed Cooling Fan Relay Control Circuit(s) |
| DTC P1258 | Engine Coolant Over Temperature - Fuel Disabled |
DIAGNOSTIC CODE INDEX
Diagnostic Starting Point - Engine Cooling
Begin the system diagnosis with the diagnostic system check. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information. The Diagnostic System Check - Vehicle will provide the following information
- The identification of the control modules which command the system
- The ability of the control modules to communicate through the serial data circuits
- The identification of any stored DTCs and their status
The use of the Diagnostic System Check - Vehicle will identify the correct procedure for diagnosing the system and where the procedure is located.
Scan Tool Output Controls
| Scan Tool Output Control | Additional Menu Selection(s) | Description |
|---|---|---|
| A/C Request | Output Control | The HVAC control module sends out a A/C request signal to turn on the A/C compressor when you select ON. The request signal should stay active until commanded OFF. |
| Blower Motor | Output Control | The HVAC control module commands the blower motor Off, Low or High. |
| Defrost Door | Output Control | The HVAC control module commands the Defrost actuator towards 255 counts when you select ON. The HVAC control module commands the Defrost actuator towards 0 counts when commanded OFF. |
| Mode Door | Output Control | The HVAC control module commands the Mode actuator towards 255 counts when you select ON. The HVAC control module commands the Mode actuator towards 0 counts when commanded OFF. |
| Driver Air Temperature Door | Output Control | The HVAC control module commands the left air temperature actuator towards 255 counts when you select ON. The HVAC control module commands the left air temperature actuator towards 0 counts when commanded OFF. |
| Passenger Air Temperature Door | Output Control | The HVAC control module commands the right air temperature actuator towards 255 counts when you select ON. The HVAC control module commands the right air temperature actuator towards 0 counts when commanded OFF. |
| Recirculation Door | Output Control | The HVAC control module commands the recirculation actuator towards 0 counts when you select ON. The HVAC control module commands the recirculation actuator towards 255 counts when you select OFF. |
| Aux. Air Temperature Door | Output Control | The HVAC control module commands the auxiliary air temperature actuator towards 255 counts when you select ON. The HVAC control module commands the auxiliary air temperature actuator towards 0 counts when commanded OFF. |
| Aux. Mode Door | Output Control | The HVAC control module commands the auxiliary Mode actuator towards 255 counts when you select ON. The HVAC control module commands the auxiliary Mode actuator towards 0 counts when commanded OFF. |
| Recalibrate Motors | Output Control | The scan tool displays Commanded State: None or On. This functions commands all actuators to their fully opened and fully closed positions and relearns these endpoints. |
| Rear Defrost Request | Output Control | The HVAC control module sends out a Rear Defrost Request signal to turn on the Rear Defrost when you select ON. |
| A/C Switch LED | Output Control | The scan tool displays Commanded State: On or Off. This functions commands the A/C LED On or Off. |
| Rear Defrost LED | Output Control | The scan tool displays Commanded State: On or Off. This functions commands the Rear Defrost LED On or Off. |
| All LEDs On | Output Control | The scan tool displays Commanded State: On or Off. This functions commands all LEDs On or Off. |
| Blower Motor Speed control | Output Control | The scan tool displays Commanded State: Off, On Not Set High or On and Set High. |
| Aux. Blower Motor Speed | Output Control | This functions commands Auxiliary Blower Motor On or Off. |
| Driver Heated Seat LED | Output Control | The scan tool displays Commanded State: On or Off. This functions commands the Driver Heated Seat LED On or Off. |
| Passenger Heated Seat LED | Output Control | The scan tool displays Commanded State: On or Off. This functions commands the Passenger Heated Seat LED On or Off. |
| Driver Heated Seat Request | Output Control | The scan tool displays Commanded State: High, Low or Off. This functions commands the Driver Heated Seat. |
| Passenger Heated Seat Request | Output Control | The scan tool displays Commanded State: High, Low or Off. This functions commands the Passenger Heated Seat. |
HVAC Control Module Scan Tool Output Controls
| Scan Tool Output Control | Additional Menu Selection(s) | Description |
|---|---|---|
| A/C Relay | Engine Output Controls | The powertrain control module (PCM) or engine control module (ECM) energizes the A/C compressor clutch relay when you select ON. The A/C compressor clutch should remain engaged until commanded OFF. |
PCM 3.5L (LX9)/ECM 3.9L (LZ9) Scan Tool Output Controls
Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Operating Conditions: Engine Idling, A/C ON, Ambient Air Temperature Between 22-27°C (70-80°F) | |||
| A/C Request | HVAC | Yes/No | Varies |
| Recirculation Dr. Position | HVAC | Counts | Varies |
| Recirculation Dr. Motor Command | HVAC | Counts | Varies |
| Mode Dr. Position | HVAC | Counts | Varies |
| Mode Dr. Motor Command | HVAC | Counts | Varies |
| Defrost Dr. Position | HVAC | Counts | Varies |
| Defrost Dr. Motor Command | HVAC | Counts | Varies |
| Driver Temp. Dr. Position | HVAC | Counts | Varies |
| Driver Temp. Dr. Motor Command | HVAC | Counts | Varies |
| Psgr. Temp. Dr. Position | HVAC | Counts | Varies |
| Psgr. Temp. Dr. Motor Command | HVAC | Counts | Varies |
| Aux. Mode Dr. Position | HVAC | Counts | Varies |
| Aux. Mode Dr. Motor Command | HVAC | Counts | Varies |
| Aux. Temp. Dr. Position | HVAC | Counts | Varies |
| Aux. Temp. Dr. Motor Command | HVAC | Counts | Varies |
| Evaporator Temp. Sensor | HVAC | °C/°F | Varies |
| Evaporator Temp. Sensor | HVAC | Counts | Varies |
| Mode Status | HVAC | Recirc/Vent/Mix-Blend/Floor/Bi-Level/Defrost | Varies |
| A/C LED | HVAC | On/Off | Varies |
| Rear Defrost LED | HVAC | On/Off | Varies |
| Driver Heated Seat Status | HVAC | Off/Low Heat/High Heat | Varies |
| Passenger Heated Seat Status | HVAC | Off/Low Heat/High Heat | Varies |
| Blower Motor Switch Position | HVAC | Off/On but not High Blower/On and High Blower | Varies |
| Aux. Blower Motor Speed Command | HVAC | Counts | Varies |
| Aux. Blower Motor Switch Position | HVAC | Aux/Off/1/2/3/4 | Varies |
| Aux. Blower Motor Speed | HVAC | Counts | Varies |
HVAC Control Module Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Operating Conditions: Engine Idling, A/C ON, Ambient Air Temperature Between 22-27°C (70-80°F) | |||
| A/C Disengage Reason | HVAC | None/WOT/System Voltage/CKP Learn Active/Engine Run Time/Coolant Hot/Stall Prevention/A/C Pressure/Engine Speed/Trans Engine Speed/A/C Pressure Sensor/Low Voltage/High Voltage/Outside Air Temp/Switched OFF | Varies |
| A/C Off for WOT | HVAC | Yes/No | Varies |
| A/C Pressure Disable | HVAC | Yes/No | Varies |
| A/C High Side Pressure | HVAC | KPa/Psi | Varies |
| A/C High Side Pressure | HVAC | Volts | Varies |
| A/C Relay Command | HVAC | On/Off | Varies |
| A/C Relay Circuit History | HVAC | OK/Open/Short/Invalid State | Varies |
| A/C Request Signal | HVAC | Yes/No | Varies |
PCM Scan Tool Data List 3.5L (LX9)/ECM 3.9L (LZ9)
Circuit Description
Battery positive voltage is supplied to the cooling fan 1 relay from the COOL FAN #1 fuse. The powertrain control module (PCM) or engine control module (ECM) controls the cooling fan 1 relay by grounding the low speed cooling fan relay control circuit via an internal solid state device called a driver.
Battery positive voltage is supplied to the cooling fan 2 relay and the cooling fan 3 relay from the COOL FAN #2 fuse. The PCM/ECM controls the relays by grounding the high speed cooling fan relay control circuit.
When the PCM/ECM is commanding a relay on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM/ECM is commanding the control circuit to a relay, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.
The PCM/ECM will monitor the control circuit for the following conditions
- A short to ground
- A short to voltage
- An open circuit
- An open relay coil
- An internally shorted or excessively low resistance relay coil
When the PCM/ECM detects any of the above conditions, the DTC will set and the affected driver will be disabled.
DTC Descriptors
This diagnostic procedure supports the following DTCs
- DTC P0480 Low Speed Cooling Fan Relay Control Circuit
- DTC P0481 High Speed Cooling Fan Relay Control Circuit
Conditions for Running the DTC
- The ignition is ON.
- System voltage is between 9-18 volts.
- The relay control circuit transitions from OFF to ON or ON to OFF.
Conditions for Setting the DTC
- The PCM/ECM detects an open, a short to ground or a short to voltage on the cooling fan relay control circuit.
- The above conditions are present for at least 30 seconds.
Action Taken When the DTC Sets
- The PCM/ECM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
- The PCM/ECM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
Conditions for Clearing the MIL/DTC
- The PCM/ECM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
- The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
- The DTC can be cleared by using the scan tool.
Diagnostic Aids
- If the condition is not present, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-241671-S27410119602006081100000) .
- Review the Freeze Frame/Failure Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
The powertrain control module (PCM) or engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 128°C (262°F). When an over temperature condition is present, DTC P1258 will set. The PCM/ECM will disable two groups of cylinders by turning OFF the fuel injectors. By switching between the two groups of cylinders, the PCM/ECM is able to reduce the temperature of the coolant.
DTC Descriptor
This diagnostic procedure supports the following DTC
DTC P1258 Engine Coolant Over Temperature - Fuel Disabled
The ignition is ON.
- The PCM/ECM detects an engine metal over temperature.
- The above condition is present for at least 8 seconds.
- The PCM/ECM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
- The PCM/ECM will signal the instrument panel cluster (IPC) to turn ON the Service Engine Soon indicator.
- The PCM/ECM will alternately disable two groups of cylinders by turning OFF the fuel injectors.
- The PCM/ECM will store conditions which were present when the DTC set as Freeze Frame and File Records data.
- A history DTC is stored.
- The PCM/ECM will turn the MIL OFF after three consecutive trips that the diagnostic has been run and passed.
- The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
- The DTC can be cleared by using the scan tool Clear DTC Information function.
| Step | Action | Yes | No |
|---|---|---|---|
| Connector End View Reference: Cooling System Connector End Views | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 2 | Check the engine cooling fans for proper operation. Are the engine cooling fans operative? | Go to Engine Overheating | Go to Symptoms - Engine Cooling |
DTC P1258
Symptoms - Engine Cooling
| IMPORTANT | Review the system operation in order to familiarize yourself with the system functions. Refer to Cooling System Description and Operation . |
Visual/Physical Inspection
- Inspect for aftermarket devices which could affect the operation of the Cooling System. Refer to «Checking Aftermarket Accessories»(ref-241671-S33907418562006081100000) in Wiring Systems.
- Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
- Inspect the surge tank reservoir for the proper coolant level.
Symptom List
Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom
- «Engine Coolant Temperature Indicator Always On»(ref-241700-S01019588332006081100000)
- «Cooling Fan Always On»(ref-241700-S09079296632006081100000)
- «Cooling Fan Inoperative»(ref-241700-S05184285872006081100000)
- «Engine Overheating»(ref-241700-S12386029702006081100000)
- «Loss of Coolant»(ref-241700-S08149533912006081100000)
- «Thermostat Diagnosis»(ref-241700-S07705280512006081100000)
- «Coolant Heater Inoperative»(ref-241700-S29713399742006081100000)
- «Engine Fails To Reach Normal Operating Temperature»(ref-241700-S16826870502006081100000)
Thermostat Diagnosis
| Step | Action | Yes | No |
|---|---|---|---|
| IMPORTANT: The temperature stick is a pencil-like device that has a wax material containing certain chemicals which melt at a given temperature. Use the temperature sticks to determine a thermostat's operating temperature by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing. The marks made by the sticks should melt when coolant temperatures reach 87°C (188°F) and 97°C (206°F), respectively. These temperatures are the normal operating range of the thermostat. | |||
| 1 | Remove the radiator cap. Rub a 87°C (188°F) and a 97°C (206°F) J 24731 on the engine water outlet housing which connects to the radiator inlet hose. See Special Tools . Warm up the engine at fast idle. Check for coolant flow before engine reaches proper operating temperature. Is there coolant flow before either mark begins to melt? | Go to Step 2 | Go to Step 3 |
| 2 | The thermostat may be stuck open, prematurely opening or missing. Replace the thermostat. Refer to WATER OUTLET AND THERMOSTAT REMOVAL (3.5L) or WATER OUTLET AND THERMOSTAT REMOVAL (3.9L) . Recheck the thermostat opening temperature as in Step 1. Does the engine still fail to reach proper operating temperature? | Go to Engine Fails To Reach Normal Operating Temperature | System OK |
| 3 | Does the coolant begin to flow by the time one or both of the temperature stick marks on the engine water outlet housing begin to melt? | System OK | Go to Step 4 |
| 4 | The thermostat may be stuck closed or opening too slowly. Replace the thermostat. Refer to WATER OUTLET AND THERMOSTAT REMOVAL (3.5L) or WATER OUTLET AND THERMOSTAT REMOVAL (3.9L) . Recheck the thermostat opening temperature as in Step 1. Does the engine still overheat? | Go to Engine Overheating | System OK |
| IMPORTANT |
|---|
| The temperature stick is a pencil-like device that has a wax material containing certain chemicals which melt at a given temperature. Use the temperature sticks to determine a thermostat's operating temperature by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing. The marks made by the sticks should melt when coolant temperatures reach 87°C (188°F) and 97°C (206°F), respectively. These temperatures are the normal operating range of the thermostat. |
Thermostat Diagnosis
Test Procedure
- Remove the pressure cap.
- Wash the pressure cap sealing surface with water.
- Use the J 24460-01 in order to test the pressure cap. See «Special Tools»(ref-241700-S25298036542006081100000) .
- Test the pressure cap for the following conditions: Pressure release when the J 24460-01 exceeds the pressure rating of the pressure cap. See «Special Tools»(ref-241700-S25298036542006081100000) . Maintain the rated pressure for at least 10 seconds.
- Replace the pressure cap under the following conditions: The pressure cap does not release pressure which exceeds the rated pressure of the cap. The pressure cap does not hold the rated pressure.
- Remove the pressure cap.
- Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(ref-241700-S27555331862006081100000) .
- Use the J 24460-01 in order to apply pressure to the cooling system. See «Special Tools»(ref-241700-S25298036542006081100000) . Do not exceed the pressure cap rating.
- The cooling system should hold the rated pressure for at least 2 minutes. Observe the gage for any pressure loss.
- Repair any leaks as required.