Home ReviewsRefund
Home/Chevrolet/TrailBlazer/Chevrolet TrailBlazer I рестайлинг (2005-2009)/Repair manual/Cooling System (Mechanical)/Engine Cooling System: Diagnosis
Contents Section: Cooling System (Mechanical) All sections

Engine Cooling System: Diagnosis Chevrolet TrailBlazer I рестайлинг

Cooling System (Mechanical) ~3455 words

DIAGNOSTIC CODE INDEX

DTCDescription
DTC P0480Cooling Fan 1 Control Circuit
DTC P0483 or P0493Cooling Fan System Performance Or Overspeed
DTC P0495Cooling Fan Speed High
DTC P0526Cooling Fan Speed Sensor Circuit
DTC P1258Engine Coolant Overtemperature - Protection Mode Active
DTC P1482Cooling Fan Speed Output Circuit

DIAGNOSTIC CODE INDEX

Diagnostic Starting Point - Engine Cooling

Begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic System Check will provide the following information

  1. The identification of the control modules which command the system
  2. The ability of the control modules to communicate through the serial data circuit
  3. 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 ControlAdditional Menu Selection(s)Description
Electro-viscous FanThe scan tool displays a Commanded State of None or percentage. This allows you to communicate with the PCM to increase or decrease the cooling fan speed in 10% increments.

PCM - 4.2L, 5.3L

Scan Tool Data List

Scan Tool ParameterData ListUnits DisplayedTypical Data Value
Ignition Switch in RUN/Engine Running/Automatic Transmission in PARK/Manual Transmission in NEUTRAL/Air Conditioner is OFF
ECT SensorENG 1, ENG 2, ENG 3, EVAP, Misfire, HO2SDegrees°C/°F
IAT SensorENG 1, ENG 2, ENG 3, EVAP, Misfire, HO2SDegrees°C/°F

Powertrain Control Module (PCM) 4.2 L (LL8), 5.3L (LM4)

Scan Tool ParameterData ListUnits DisplayedTypical Data Value
Ignition Switch in RUN/Engine Running/Automatic Transmission in PARK/Manual Transmission in NEUTRAL/Air Conditioner is OFF
Displayed Coolant TempData 1°C/°FVaries
Monitored Coolant TempData 1°C/°FVaries

Instrument Panel Cluster

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(ref-277748-S10358011192008011800000) prior to using this diagnostic procedure.
  2. «Strategy Based Diagnosis»(ref-277748-S03649418562008011800000)
  3. «Diagnostic Procedure Instructions»(ref-277748-S26411097192008011800000)

Diagnostic Fault Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Relay GroundP0483, P0493
Relay Voltage SupplyP0480, P0483, P0493P0480, P0483, P0493
Relay ControlP0480P0480P0480
Speed Sensor Low ReferenceP0483, P0493, P0526
Speed Sensor 5-Volt ReferenceP0526
Speed Sensor SignalP0526P0526P0526
Clutch GroundP0483, P0493
Clutch Voltage SupplyP0483, P0493P0483, P0493P0483, P0493, P0495

DTC P0480

Conditions for Running the DTC

  1. The engine speed is greater than 400 RPM.
  2. The ignition voltage is greater than 10 volts and less than 18 volts.

Conditions for Setting the DTC

  1. The powertrain control module (PCM) detects that the commanded state and the actual state of the control circuit do not match.
  2. The above condition is present for at least 5 seconds.

Action Taken When the DTC Sets

DTC P0480 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0480 is a Type B DTC.

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

  1. «Scan Tool Data List»(ref-277772-S29150100912008011800000)
  2. «Scan Tool Data Definitions»(ref-277744-S42469585272008011800000)
  3. «Scan Tool Output Controls»(ref-277744-S26422725862008011800000)

Circuit/System Testing

  1. Ignition OFF, disconnect the fan relay.
  2. Measure between the fan relay ground circuit terminal and ground for less than 3 ohms. If more than the specified range, test the ground circuit for an open/high resistance.
  3. Operate the engine at 2,000 RPM for 2 minutes. The fan should be quiet to indicated the clutch is disengaged. If not disengaged, test the cooling fan clutch supply voltage circuit for a short to voltage. If the circuit tests normal, replace the clutch.
  4. Ignition OFF, install a 10A fused jumper wire between the positive terminal at the battery and the cooling fan clutch supply voltage circuit terminal.
  5. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicated the clutch is engaged. If not engaged, test the cooling fan clutch supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the clutch.
  6. Ignition OFF, install a 10A fused jumper wire between the relay voltage supply circuit terminal and the cooling fan clutch supply voltage circuit terminal.
  7. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicated the clutch is engaged. If not engaged, test the relay voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  8. Connect a test lamp between the positive terminal at the battery and the cooling fan clutch relay control circuit terminal.
  9. Engine RUNNING at 2,000 RPM, command the cooling fan clutch from 10 to 80 percent. The test lamp should flash at approximately 2 Hz as its brightness varies from dim to bright. If the lamp does not flash or vary correctly, test the cooling fan clutch control circuit for a short to ground, a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.
  10. If all circuits and the control module test normal, replace the relay.

Component Testing

Relay Test

  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-277748-S10358011192008011800000) prior to using this diagnostic procedure.
  2. «Strategy Based Diagnosis»(ref-277748-S03649418562008011800000)
  3. «Diagnostic Procedure Instructions»(ref-277748-S26411097192008011800000)
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Relay GroundP0483, P0493
Relay Voltage SupplyP0480, P0483, P0493P0480, P0483, P0493
Relay ControlP0480P0480P0480
Speed Sensor Low ReferenceP0483, P0493, P0526
Speed Sensor 5-Volt ReferenceP0526
Speed Sensor SignalP0526P0526P0526
Clutch GroundP0483, P0493
Clutch Voltage SupplyP0483, P0493P0483, P0493P0483, P0493, P0495

DTC P0483 or P0493

P0483

  1. The engine is running.
  2. The system voltage is greater than 8.5 volts.
  3. The intake air temperature (IAT) is greater than -7°C (+19°F).
  4. DTCs P0480 and P0526 are not set.
  5. The engine speed is less than 3,200 RPM.
  6. The engine speed is not changing more than 250 RPM for 5 seconds.
  7. Fan command is greater than 0 percent.

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

  1. «Scan Tool Data List»(ref-277772-S29150100912008011800000)
  2. «Scan Tool Data Definitions»(ref-277744-S42469585272008011800000)
  3. «Scan Tool Output Controls»(ref-277744-S26422725862008011800000)
  1. Ignition OFF, disconnect the fan relay.
  2. Measure between the fan relay ground circuit terminal and ground for less than 3 ohms. If more than the specified range, test the ground circuit for an open/high resistance.
  3. Operate the engine at 2,000 RPM for 2 minutes. The fan should be quiet to indicated the clutch is disengaged. If not disengaged, test the cooling fan clutch supply voltage circuit for a short to voltage. If the circuit tests normal, replace the clutch.
  4. Ignition OFF, install a 10A fused jumper wire between the positive terminal at the battery and the cooling fan clutch supply voltage circuit terminal.
  5. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicated the clutch is engaged. If not engaged, test the cooling fan clutch supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the clutch.
  6. Ignition OFF, install a 10A fused jumper wire between the relay voltage supply circuit terminal and the cooling fan clutch supply voltage circuit terminal.
  7. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicated the clutch is engaged. If not engaged, test the relay voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  8. Connect a test lamp between the positive terminal at the battery and the cooling fan clutch relay control circuit terminal.
  9. Engine RUNNING at 2,000 RPM, command the cooling fan clutch from 10 to 80 percent. The test lamp should flash at approximately 2 Hz as its brightness varies from dim to bright. If the lamp does not flash or vary correctly, test the cooling fan clutch control circuit for a short to ground, a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.
  10. Perform the relay component test. The relay should test normal. If the relay does not test normal, replace the relay.
  11. Ignition OFF, disconnect the fan clutch at the shroud.
  12. Measure between the low reference circuit terminal and ground for less than 3 ohms. If more than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module.
  13. Ignition ON, measure between the 5-volt reference and the low reference circuit terminals for 4.8-5.2 volts. If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module. If more than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
  14. Install jumper wires in the 5-volt reference and low reference circuits between the harness and pigtail connectors at the shroud.
  15. Measure DC voltage between the signal circuit terminal at the sensor pigtail connector and the 5-volt reference circuit jumper wire terminal.
  16. Ignition ON, rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts. If the voltage does not toggle correctly, test the 3 circuits in the pigtail harness for a short to ground, a short to voltage or an open/high resistance. If the circuits test normal, replace the clutch.
  17. Leave the jumpers from the previous step in place. Measure voltage between the signal circuit terminals of the harness and pigtail connectors at the shroud.
  18. Rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts. If the voltage does not toggle correctly, test the signal circuit for a short to ground, a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.
  19. If all circuits, the relay and the speed sensor test normal, replace the clutch.

Relay Test

  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-277748-S10358011192008011800000) prior to using this diagnostic procedure.
  2. «Strategy Based Diagnosis»(ref-277748-S03649418562008011800000)
  3. «Diagnostic Procedure Instructions»(ref-277748-S26411097192008011800000)
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Relay GroundP0483, P0493
Relay Voltage SupplyP0480, P0483, P0493P0480, P0483, P0493
Relay ControlP0480P0480P0480
Speed Sensor Low ReferenceP0483, P0493, P0526
Speed Sensor 5-Volt ReferenceP0526
Speed Sensor SignalP0526P0526P0526
Clutch GroundP0483, P0493
Clutch Voltage SupplyP0483, P0493P0483, P0493P0483, P0493, P0495

DTC P0495

  1. The engine is running.
  2. The system voltage is greater than 8.5 volts.
  3. The intake air temperature (IAT) is greater than -7°C (+19°F).
  4. Zero percent duty cycle is commanded and the engine RPM has been over 1,800 RPM for at least 120 seconds.

Cooling fan RPM exceeds 1,600 RPM for 81 seconds.

DTC P0495 is a Type B DTC.

DTC P0495 is a Type B DTC.

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

  1. «Scan Tool Data List»(ref-277772-S29150100912008011800000)
  2. «Scan Tool Data Definitions»(ref-277744-S42469585272008011800000)
  3. «Scan Tool Output Controls»(ref-277744-S26422725862008011800000)
  1. Ignition OFF, disconnect the harness connector at the fan shroud.
  2. Operate the engine at 2,000 RPM for 2 minutes. The fan should be quiet to indicate the clutch is disengaged. If disengaged, test or replace the relay. If not disengaged, test the cooling fan clutch supply voltage circuit for a short to voltage. If the circuit tests normal, replace the clutch.

Relay Test

  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-277748-S10358011192008011800000) prior to using this diagnostic procedure.
  2. «Strategy Based Diagnosis»(ref-277748-S03649418562008011800000)
  3. «Diagnostic Procedure Instructions»(ref-277748-S26411097192008011800000)
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Relay GroundP0483, P0493
Relay Voltage SupplyP0480, P0483, P0493P0480, P0483, P0493
Relay ControlP0480P0480P0480
Speed Sensor Low ReferenceP0483, P0493, P0526
Speed Sensor 5-Volt ReferenceP0526
Speed Sensor SignalP0526P0526P0526
Clutch GroundP0483, P0493
Clutch Voltage SupplyP0483, P0493P0483, P0493P0483, P0493, P0495

DTC P0526

  1. The engine is running.
  2. System voltage is greater than 8.5 volts.
  1. The powertrain control module (PCM) has detected a loss of cooling fan speed signal.
  2. The above condition is present for at least 11 seconds.

DTC P0526 is a Type B DTC.

DTC P0526 is a Type B DTC.

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

  1. «Scan Tool Data List»(ref-277772-S29150100912008011800000)
  2. «Scan Tool Data Definitions»(ref-277744-S42469585272008011800000)
  3. «Scan Tool Output Controls»(ref-277744-S26422725862008011800000)
  1. Ignition OFF, disconnect the fan clutch at the shroud.
  2. Measure between the low reference circuit terminal and ground for less than 3 ohms. If more than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module.
  3. Ignition ON, measure between the 5-volt reference and the low reference circuit terminals for 4.8-5.2 volts. If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module. If more than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
  4. Install jumper wires in the 5-volt reference and low reference circuits between the harness and pigtail connectors at the shroud.
  5. Measure DC voltage between the signal circuit terminal at the sensor pigtail connector and the 5-volt reference circuit jumper wire terminal.
  6. Ignition ON, rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts. If the voltage does not toggle correctly, test the 3 circuits in the pigtail harness for a short to ground, a short to voltage or an open/high resistance. If the circuits test normal, replace the clutch.
  7. Leave the jumpers from the previous step in place. Measure voltage between the signal circuit terminals at the harness and pigtail connectors at the shroud.
  8. Rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts. If the voltage does not toggle correctly, test the signal circuit for a short to ground or a short to voltage. If the circuit tests normal, replace the control module.
  9. If all circuits and the speed sensor test normal, replace the engine control module (ECM).
  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-277748-S10358011192008011800000) prior to using this diagnostic procedure.
  2. «Strategy Based Diagnosis»(ref-277748-S03649418562008011800000)
  3. «Diagnostic Procedure Instructions»(ref-277748-S26411097192008011800000)
  1. The engine is running.
  2. DTCs P0117 or P0118 are not set.

Coolant temperature more than 132°C (270°F) for more than 10 seconds.

  1. DTC P1258 is a Type A DTC.
  2. The engine will operate in the Overheated Engine Protection Operating Mode.
  3. The engine coolant temperature indicator lamp, if equipped, will illuminate.
  4. The driver information center (DIC), if equipped, will display a message.

DTC P1258 is a Type A DTC.

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Engine Cooling

  1. «Scan Tool Data List»(ref-277788-S11486275762008011800000)
  2. «Scan Tool Output Controls»(ref-277788-S10858449482008011800000)
  1. Test the thermostat for correct operation. Refer to «Thermostat Diagnosis»(ref-277788-S31431398992008011800000) .
  2. Test the engine cooling system for overheating. Refer to «Engine Overheating»(ref-277788-S39483873602008011800000) .
  3. Inspect the water pump and coolant flow for correct operation. Refer to «Water Pump Replacement (LH6 and LS2)»(ref-277788-S14677872772008011800000) .
  4. Inspect the engine for worn/leaking/cracked cylinder heads and engine block. Refer to the following procedures: «Coolant in Combustion Chamber»(ref-277767-S38976004902008011800000) and «Coolant in Engine Oil»(ref-277767-S03353067812008011800000) for the 4.2L engine Coolant in Combustion Chamber and Coolant in Engine Oil for the 5.3L engine Coolant in Combustion Chamber and Coolant in Engine Oil for the 6.0L engine
  1. Perform the «Diagnostic System Check - Vehicle»(ref-277748-S10358011192008011800000) prior to using this diagnostic procedure.
  2. «Strategy Based Diagnosis»(ref-277748-S03649418562008011800000)
  3. «Diagnostic Procedure Instructions»(ref-277748-S26411097192008011800000)

Diagnostic Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Relay GroundP0483, P0493
Relay Voltage SupplyP0480, P0483, P0493, P1482P0480, P0483, P0493, P1482
Relay ControlP0480P0480P0480, P1482
Speed Sensor Low ReferenceP0483, P0493, P0526
Speed Sensor 5-Volt ReferenceP0526
Speed Sensor SignalP0526P0526P0526
Clutch GroundP0483, P0493
Clutch Voltage SupplyP0483, P0493P0483, P0493P0483, P0493, P0495

DTC P1482

  1. The engine speed is greater than 400 RPM.
  2. The ignition voltage is greater than 10 volts and less than 18 volts.
  1. The control module detects that the commanded state and the actual state of the control circuit do not match.
  2. The above condition is present for at least 5 seconds.

Action Taken When DTC Sets

DTC P1482 is a Type B DTC.

DTC P1482 is a Type B DTC.

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

  1. «Scan Tool Data List»(ref-277772-S29150100912008011800000)
  2. «Scan Tool Data Definitions»(ref-277744-S42469585272008011800000)
  3. «Scan Tool Output Controls»(ref-277744-S26422725862008011800000)
IMPORTANTYou must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
  1. Ignition OFF, disconnect the fan relay.
  2. Measure between the fan relay ground circuit terminal 6 and ground for less than 3 ohms. If more than the specified range, test the ground circuit for an open/high resistance.
  3. Operate the engine at 2,000 RPM for 2 minutes. The fan should be quiet to indicate the clutch is disengaged. If not disengaged, test the cooling fan clutch supply voltage circuit for a short to voltage. If the circuit tests normal, replace the clutch.
  4. Ignition OFF, install a 10A fused jumper wire between the positive terminal at the battery and the cooling fan clutch supply voltage circuit terminal 4.
  5. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicate the clutch is engaged. If not engaged, test the cooling fan clutch supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan clutch ground circuit for an open/high resistance. If the circuits test normal, replace the clutch.
  6. Ignition OFF, install a 10A fused jumper wire between the relay voltage supply circuit terminal 2 and the cooling fan clutch supply voltage circuit terminal 4.
  7. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicate the clutch is engaged. If not engaged, test the relay voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  8. Connect a test lamp between the positive terminal at the battery and the cooling fan clutch relay control circuit terminal 5.
  9. Engine RUNNING at 2,000 RPM, command the cooling fan clutch to 70 percent for 2 minutes. The test lamp should turn on steady or flash, indicating that the control module can control the relay. the lamp does not flash or turn on steady, test the cooling fan clutch control circuit for a short to ground, a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.
  10. If all circuits and the control module test normal, replace the relay.

Relay Test

  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the Cooling System. Refer to «Checking Aftermarket Accessories»(ref-277749-S12414982982008011800000) .
  2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

  1. «Engine Coolant Temperature Indicator Always On»(ref-277788-S37060329942008011800000)
  2. «Engine Overheating»(ref-277788-S39483873602008011800000)
  3. «Loss of Coolant»(ref-277788-S18074391732008011800000)
  4. «Thermostat Diagnosis»(ref-277788-S31431398992008011800000)
  5. «Coolant Heater Inoperative»(ref-277788-S29755695922008011800000)
  6. «Engine Fails To Reach Normal Operating Temperature»(ref-277788-S15059476022008011800000)
  7. «Excessive Fan Noise»(ref-277788-S27822573952008011800000)

Thermostat Diagnosis

StepActionYesNo
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.
1Remove 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 2Go to Step 3
2The thermostat may be stuck open, prematurely opening or missing. Replace the thermostat. Refer to Thermostat Replacement (4.2L Engine) or Thermostat Replacement (5.3L and 6.0L Engines) . 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 TemperatureSystem OK
3Does 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 OKGo to Step 4
4The thermostat may be stuck closed or opening too slowly. Replace the thermostat. Refer to Thermostat Replacement (4.2L Engine) or Thermostat Replacement (5.3L and 6.0L Engines) . Recheck the thermostat opening temperature as in Step 1. Does the engine still overheat?Go to Engine OverheatingSystem 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

IMPORTANTThe power supply cord will read open due to an internal thermal switch if the ambient temperature is above -18°C (0°F).
  1. Test the engine coolant heater for an open or short to ground. If open or shorted, replace the heater.
  2. If the heater tests normal, replace the coolant heater power cord.

Pressure Cap Testing

  1. Remove the pressure cap.
  2. Wash the pressure cap sealing surface with water.
  3. Use the J 24460-01 (1) with J 42401 (2) in order to test the pressure cap. See «Special Tools»(ref-277788-S20027075962008011800000) .
  4. 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-277788-S20027075962008011800000) . Maintain the rated pressure for at least 10 seconds. Note the rate of pressure loss.
  5. 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.

Testing Procedure

  1. Remove the pressure cap.
  2. Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(ref-277788-S06113734712008011800000) .
  3. Wash the pressure cap mating surface with water.
  4. Use the J 24460-01 in order to apply pressure to the cooling system. See «Special Tools»(ref-277788-S20027075962008011800000) . Do not exceed the pressure cap rating.
  5. The cooling system should hold the rated pressure for at least 2 minutes. Observe the gauge for any pressure loss.
  6. Repair any leaks as required.

Circuit Description

The electro-viscous clutch is controlled by the powertrain control module (PCM). The PCM controls a solenoid that regulates a fluid pressure that controls slip of the fan clutch. Internal to the fan is a centrifugal fluid pump, solenoid, hall effect sensor, valve lever and hydraulic fluid. There are 2 chambers for the fluid. These 2 chambers are separated by a valve lever. The first chamber is the storage chamber, which holds excess fluid. The second chamber is the working chamber. As the pressure of the fluid is increased in the working chamber, the amount of slip the fan has is decreased. The position of the valve lever is controlled by an electric solenoid.

Diagnostic Aids

  1. Turning OFF the engine when the cooling fan clutch is engaged, the cooling fan clutch will be engaged at engine restart. This may cause an excessive noise concern. This is a normal condition.
  2. If the engine is turned OFF for an extended period of time, usually over night, the hydraulic fluid may fill working chamber and cause limited slip at engine restart. This may cause the excessive noise condition. This is a normal condition.
  3. To engage the cooling fan clutch, it can take up to 2 minutes for a 100 percent command with the engine at 2,000 RPM. The lower the engine speed, the longer it will take the cooling fan clutch to engage.
  4. To disengage the cooling fan clutch, it can take up to 2 minutes with the engine at 2,000 RPM. The lower the engine speed, the longer it will take to disengage.
  5. In lower ambient air temperatures the cooling fan clutch will engage in less time, however it will take longer to disengage.
  6. An inline connector could cause an intermittent DTC. Ensure to test for poor connections and pin retention at all inline connectors. Refer to system schematics for connector and locations.
  7. If the condition is not present, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277749-S41598039092008011800000) .

More articles — Engine Cooling System