Diagnostic Starting Point - Engine Cooling
Begin the system diagnosis with the DIAGNOSTIC SYSTEM CHECK - Engine Cooling . The Diagnostic System Check will provide the following information
- The identification of the control module(s) which command the system.
- The ability of the control module(s) to communicate through the serial data circuit.
- The identification of any stored diagnostic trouble codes (DTCs) and their status.
The use of the Diagnostic System Check 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 |
|---|---|---|
| Check Coolant Temp | Lamp Test | Command the instrument cluster message center module to activate the output. The scan tool will displays the status of the selected output. This status information represents only what the scan tool has commanded, not what action was actually taken. |
| Check Engine Temp | Lamp Test | Command the instrument cluster message center module to activate the output. The scan tool will displays the status of the selected output. This status information represents only what the scan tool has commanded, not what action was actually taken. |
| Low Coolant | Lamp Test | Command the instrument cluster message center module to activate the output. The scan tool will displays the status of the selected output. This status information represents only what the scan tool has commanded, not what action was actually taken. |
| Reduced Engine Power | Lamp Test | Command the instrument cluster message center module to activate the output. The scan tool will displays the status of the selected output. This status information represents only what the scan tool has commanded, not what action was actually taken. |
Instrument Cluster Scan Tool Output Controls
Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Ignition Switch in RUN/Engine running/Automatic Transmission in PARK/Manual Transmission in NEUTRAL/Air Conditioner is OFF | |||
| Check Coolant Temp | Outputs | On/Off | Off |
| Check Engine Temp | Outputs | On/Off | Off |
| Displayed Coolant Temp | Data | Celsius (C)/Fahrenheit (F) | 87°C (189°F) |
| Low Coolant | Outputs | On/Off | Off |
| Monitored Coolant Temp | Data | Celsius (C)/Fahrenheit (F) | 87°C (Fluctuates range 82-93°C) 189°F (Fluctuates range 180-200°F) |
| Reduced Engine Power | Outputs | On/Off | Off |
Instrument Panel Cluster (IPC) Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Ignition Switch in RUN/Engine running/Automatic Transmission in PARK/Manual Transmission in NEUTRAL/Air Conditioner is OFF | |||
| Coolant Level Switch | Engine Data 2 | Low/OK | OK |
| ECT Sensor | Engine Data 2 | Degrees | 87°C (189°F) |
Powertrain Control Module (PCM) 4.3L Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Ignition Switch in RUN/Engine running/Automatic Transmission in PARK/Manual Transmission in NEUTRAL/Air Conditioner is OFF | |||
| Coolant Level Switch | Engine Data 2 | Low/OK | OK |
| ECT Sensor | Engine Data 1 Engine Data 2 | Degrees | 87°C (189°F) |
Powertrain Control Module (PCM) 4.8L, 5.3L, and 6.0L Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Ignition Switch in RUN/Engine running/Automatic Transmission in PARK/Manual Transmission in NEUTRAL/Air Conditioner is OFF | |||
| Coolant Level Switch | Engine Data 2 | Low/OK | No |
| ECT | Engine Data 1 Engine Data 2 Engine Data 3 | Degrees | 87°C (189°F) |
Powertrain Control Module (PCM) 8.1L Scan Tool Data List
Diagnostic Trouble Code (DTC) List
| DTC | Diagnostic Procedure | Module |
|---|---|---|
| P1258 | DTC P1258 | PCM |
Diagnostic Trouble Code (DTC) List
Circuit Description
The PCM uses the ECT sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 132°C (270°F). When an over temperature condition is present, DTC P1258 will set. The PCM will disable two groups of four cylinders by turning OFF the fuel injectors. By switching between the two groups of cylinders, the PCM is able to reduce the temperature of the coolant.
Conditions for Running the DTC
- DTCs P0117, P0118, P1114, and P1115 are not active.
- The engine is running.
Conditions for Setting the DTC
The engine coolant temperature is above 132°C (270°F) for 10 seconds or more.
Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
- The PCM will signal the IPC to turn ON the Service Engine Soon indicator.
- The PCM will alternately disable two groups of four cylinders by turning OFF the fuel injectors.
- The PCM will store conditions which were present when the DTC set as Freeze Frame and File Records data.
Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL OFF after 3 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 | Was the Diagnostic System Check for Engine Cooling performed? | Go to Step 2 | Go to DIAGNOSTIC SYSTEM CHECK - Engine Cooling |
| 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-175720-S08180388062005042600000) .
- 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 Overheated Indicator Always On»(ref-175731-S12960397882005091200000)
- «Engine Coolant Temperature Indicator Always On»(ref-175731-S07309687932005091200000)
- «Low Engine Coolant Indicator Always On»(ref-175731-S18779127282005042600000)
- «Coolant Heater Inoperative»(ref-175731-S36749600702005091200000)
- «Engine Overheating»(ref-175731-S38305142452005090100000)
- «Loss of Coolant»(ref-175731-S01304529072005090100000)
- «Thermostat Diagnosis»(ref-175731-S40687796732005042600000)
- «Engine Fails To Reach Normal Operating Temperature»(ref-175731-S15841333742005091200000)
- «Fan Clutch Diagnosis»(ref-175731-S01248418132005091200000)
Thermostat Test Procedure Using Tempil Sticks
The coolant thermostat can be tested using a temperature (tempil) stick. The temperature stick is a pencil like device. It has a wax material containing certain chemicals which melt at a given temperature. Temperature sticks can be used to determine a thermostat's operating range, by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing.
- Use a tempil stick in order to find the opening and the closing temperatures of the coolant thermostat. J 24731 -188 tempil stick melts at 87°C (188°F). The thermostat should begin to open. J 24731 -206 tempil stick melts at 97°C (206°F). The thermostat should be fully open.
- Replace the coolant thermostat if it does not operate properly between this temperature range.
Thermostat Test Procedure Using Glycol
Inspect the operation of the thermostat by hanging the thermostat on a hook in a 50/50 percent solution of DEX-COOL® and clean drinkable water.
In order to inspect if the thermostat valve is opening properly, perform the following test
- Completely submerge the thermostat in the glycol solution. The solution should be 11°C (22°F) above the temperature indicated on the thermostat valve.
- Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.
In order to inspect if the thermostat valve is closing properly, perform the following test
- Completely submerge the thermostat in a glycol solution. The solution should be 6°C (10°F) below the temperature indicated on the thermostat valve.
- Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.
Pressure Cap Testing
Tools Required
J 24460-01 Cooling System Pressure Tester
- Remove the pressure cap.
- Wash the pressure cap sealing surface with water.
- Use the J 24460-01 in order to test the pressure cap.
- Test the pressure cap for the following conditions: Pressure release when the J 24460-01 exceeds the pressure rating of the pressure cap. 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.
Cooling System Leak Testing
Tools Required
J 24460-01 Cooling System Pressure Tester
- Remove the pressure cap.
- Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(ref-175731-S34431030292005042600000) .
- Use the J 24460-01 in order to apply pressure to the cooling system. 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.
Fan Clutch Diagnosis
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Were you sent here from Symptoms or another diagnostic table? | Go to Step 2 | Go to SYMPTOMS - Engine Cooling |
| 2 | Is there excessive fan air noise? | Go to Step 3 | Go to Step 4 |
| 3 | Fan air noise is normal during cold engine start up. Does the fan noise go away at normal engine operating temperature? | Go to Step 13 | Go to Step 4 |
| 4 | IMPORTANT: The engine must be turned OFF and the engine temperature should be cold. Rotate the fan clutch.Does the fan clutch rotate? | Go to Step 5 | Go to Step 14 |
| 5 | Visually inspect the fan blades for cracks, looseness or damage. Are the fan blades in good condition? | Go to Step 6 | Go to Step 15 |
| 6 | Visually inspect the fan clutch for signs of silicone leakage. Slight silicone leakage may not effect the fan clutch engagement. Excess leakage will prevent the fan clutch from engaging. Is the silicone fluid leakage excessive? | Go to Step 14 | Go to Step 7 |
| 7 | Inspect the fan clutch for proper installation. Move the fan blade back and forth in a lateral motion. Inspect for fan blade to fan clutch movement. Is the fan blade loose at the fan clutch? | Go to Step 10 | Go to Step 8 |
| 8 | Inspect the fan clutch for wear. Move the fan blade back and forth in a lateral motion. IMPORTANT: Approximately 6.5 mm (1/4 in) movement at the tip of the fan blade is normal. Inspect for fan clutch lateral movement. Is the fan clutch lateral movement excessive? | Go to Step 14 | Go to Step 9 |
| 9 | The fan clutch should have more turning resistance when the engine is at or above normal operating temperature. Does the fan clutch have more resistance when the engine temperature is raised? | Go to Step 11 | Go to Step 14 |
| 10 | Tighten the fan. Refer to Fastener Tightening Specifications . Is the repair complete? | Go to Step 16 | |
| 11 | Perform a fan clutch engagement test. Ensure the engine coolant level is full. Ensure the cooling fan drive belt tension is correct and not slipping. Position and secure a thermometer between the fan clutch and the radiator. Ensure the cooling fan is disengaged before starting this test. Sufficiently cover the radiator grille to restrict the air flow. IMPORTANT: Do not allow engine temperature to exceed 121°C (250°F). Start the engine. Turn the A/C ON, if equipped. Operate the engine at approximately 2,000 RPM. Inspect the thermometer reading when the fan clutch engages. Do not continue this test if the fan clutch does not engage between 85-96°C (185-205°F). Fan clutch engagement will be indicated by an increase in fan air noise, fan speed, and a drop of about 3-10°C (5-15°F) on the thermometer reading. Did the fan clutch engage between 85-96°C (185-205°F)? | Go to Step 12 | Go to Step 14 |
| 12 | Once the fan clutch engages, perform the following steps: Uncover the radiator grille. Turn the A/C OFF, if equipped. Operate the engine at approximately 2,500 RPM to reduce the engine operating temperature. Remove the thermometer. Did the engine return to normal operating temperature? | Go to Step 13 | |
| 13 | As the engine temperature returns to normal, the fan clutch will disengage, indicated by a reduction in fan air noise and fan speed. Did the fan clutch disengage? | Go to Step 16 | Go to Step 14 |
| 14 | Replace the fan clutch. Refer to Fan Clutch Replacement . Is the repair complete? | Go to Step 16 | |
| 15 | Replace the fan blades. Refer to Fan Replacement . Is the repair complete? | Go to Step 16 | |
| 16 | Operate the fan clutch to verify proper operation. Did you find and correct the condition? | System OK | Go to Step 2 |
| IMPORTANT |
|---|
| The engine must be turned OFF and the engine temperature should be cold. |
| IMPORTANT |
|---|
| Approximately 6.5 mm (1/4 in) movement at the tip of the fan blade is normal. |
| IMPORTANT |
|---|
| Do not allow engine temperature to exceed 121°C (250°F). |
Fan Clutch Diagnosis