Engine Cooling System: Diagnosis Chevrolet TrailBlazer I

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

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 Data Definitions

Desired Fan Speed: This parameter indicates the desired cooling fan speed in RPM. This value is determined by engine load, temperature, and speed.

Displayed Coolant Temperature - Range

32-127°C (89-260°F): This data is the coolant temperature the Instrument Cluster is attempting to display on the coolant temperature gauge. This data may differ from the monitored coolant temperature for a period of time due to filtering. The data may also differ from the monitored coolant temperature when coolant temperature is not in the range of 71-127°C (160-260°F) since the display is limited to these values. If a Class 2 communication failure occurs, this data will be at the minimum value of 32°C (89°F).

ECT Sensor: The scan tool displays -40°C to 151°C (-40°F to 304°F). The Engine Coolant Temperature (ECT) sensor is mounted in the coolant stream. The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold and internal resistance is high, the PCM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms and internal resistance decreases, the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.

Fan Speed: This parameter indicates the actual speed of the cooling fan in RPM.

IAT Sensor: The scan tool displays -40°C to 151°C (-40°F to 304°F). The PCM converts the signal of the IAT sensor into degrees. The PCM uses the IAT in order to adjust fuel delivery, spark timing, and cooling fan speed according to the incoming air temperature.

Monitored Coolant Temperature - Range

40-215°C (40-419°F): This data is the clusters measurement of the engine coolant temperature as provided by the PCM on the Class 2 serial data line.

Scheme 27

Circuit Description

The powertrain control module (PCM) sends a pulse width modulation (PWM) signal of 0-12 volts via the cooling fan clutch control circuit to the cooling fan relay. The PCM monitors the cooling fan clutch control circuit during vehicle operation. When the cooling fan clutch is commanded on by the PCM, the control circuit is at a low voltage. When the cooling fan clutch is commanded off, the control circuit is near battery voltage. The PCM uses this PWM to control the position of the oil control valve located inside the cooling fan clutch. If during operation, the PCM detects an improper circuit condition on the cooling fan clutch control circuit DTC P0480 will set.

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 PCM detects that the commanded state of the relay 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

1. The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM stores the conditions present when the DTC sets as Freeze Frame/Failure Records data.
3. The PCM commands the cooling fan clutch to 100%.

Conditions for Clearing the MIL/DTC

1. The PCM turns OFF the malfunction indicator lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

1. 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 connectors and locations.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. Disconnect the harness connector of the cooling fan from the shroud. Inspect the exposed wires between the harness connector and the tubing.

The following DTCs are for the cooling fan clutch.

1. P0483 is for the difference of the commanded cooling fan speed compared to actual cooling fan speed is greater than 1000 RPM.
2. P0493 is for a cooling fan clutch over speed condition, approximately 6800 RPM.

The cooling fan relay sends a pulse width modulation (PWM) signal of 12-14 volts to the cooling fan clutch through the cooling fan clutch supply voltage circuit. The powertrain control module (PCM) uses this PWM signal in order to control the speed of the cooling fan clutch. The signal controls the position of the oil control valve inside the cooling fan clutch. If the cooling fan RPM is different than the PCM is expecting, DTC P0483 will set. The actual cooling fan RPM vs the desired cooling fan RPM is not always exactly the same. There can be up to an 800 RPM difference. If the PCM detects that the cooling fan speed is over 6800 RPM then DTC P0493 will set.

1. For DTC P0483: The engine is running. The system voltage is greater than 8.5 volts. The intake air temperature (IAT) is greater than -7°C (19°F). DTCs P0480 and P0526 are not set. The engine speed is less than 3200 RPM. The engine speed is not changing more than 250 RPM for 5 seconds. Fan command is greater than 0%.
2. For DTC P0493 is that the engine is running.

1. For DTC P0483 is the difference between commanded and actual cooling fan speed is greater than 1000 RPM for 100 seconds.
2. For DTC P0493 the cooling fan RPM is greater than 6800 RPM.

1. For DTC P0483: The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. The PCM will store the conditions as Freeze Frame/Failure Records data. The PCM commands the cooling fan clutch to 100%.
2. For DTC P0493: The Reduced Engine Power indicator illuminates. The PCM will store the conditions as Freeze Frame/Failure Records data.

The PCM turns OFF the MIL after the third consecutive trip that the diagnostic test has run and passed.

1. 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.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. Disconnect the harness connector of the cooling fan clutch from the shroud. Inspect the exposed wires between the harness connector and the tubing.

The cooling fan relay sends a pulse width modulation (PWM) signal (12-14 volts) to the cooling fan by the cooling fan clutch supply voltage circuit. The powertrain control module (PCM) uses the PWM signal, which controls the speed of the cooling fan clutch by controlling the position of the oil control valve inside the clutch. If the cooling fan clutch RPM is to high when the PCM is commanding 0%, DTC P0495 will set.

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 1800 RPM for at least 120 seconds.

Cooling fan RPM exceeds 1600 RPM for 81 seconds.

1. The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM will store the conditions as Freeze Frame/Failure Records data.

1. The PCM turns the MIL OFF after the third consecutive trip that the diagnostic procedure has run and passed.
2. Clear the DTC using the Clear DTC Information function of the scan tool.

1. 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.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. If DTCs P0495 and P0113 are set and the weather is cold, the cooling fan code may be false. Clear DTC P0495, and after an IAT repair, check if the DTC will reset.

The powertrain control module (PCM) uses the cooling fan speed signal in order to determine the actual fan speed in relation to the desired fan speed. The PCM uses the cooling fan speed signal in order to reduce the cooling fan noise and in order to maintain the powertrain cooling requirements. The PCM supplies power and ground to the clutch hall effect sensor of the cooling fan clutch. The hall effect sensor returns a signal pulse through the speed signal circuit in response to the reluctor track, which is located inside the fan clutch. If during operation, the PCM detects a loss of the cooling fan speed signal, DTC P0526 will set.

1. The engine is running.
2. System voltage is greater than 8.5 volts.

1. The PCM has detected a loss of cooling fan speed signal.
2. The above condition is present for at least 11 seconds.

1. The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM will store the condition as Freeze Frame/Failure Records data.
3. The PCM commands the cooling fan to 100%.

1. The PCM turns OFF the malfunction indicator lamp (MIL) after the third consecutive trip that the diagnostic test has run and passed.
2. Clear the DTC by using the Clear DTC Information function of the scan tool.

1. 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 connectors and locations.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. Disconnect the harness connector of the cooling fan clutch from the shroud. Inspect the exposed wires between the harness connector and the tubing.
4. Inspect the cooling fan clutch harness in order to ensure that the clutch supply voltage circuit is not shorted to the following circuits: The 5-volt reference circuit. The cooling fan speed signal circuit. The low reference circuit.
5. DTC P0526 will set if the engine is started without the drive belt ON.

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.

1. DTCS P0117, P0118, P1114, and P1115 are not active.
2. The engine is running.

The engine coolant temperature is above 132°C (270°F) for 10 seconds or more.

1. The PCM will illuminate the malfunction indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
2. The PCM will signal the IPC to turn ON the Service Engine Soon indicator.
3. The PCM will alternately disable two groups of four cylinders by turning OFF the fuel injectors.
4. The PCM will store conditions which were present when the DTC set as Freeze Frame and File Records data.

1. The PCM will turn the MIL OFF after 3 consecutive trips that the diagnostic has been run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using the scan tool Clear DTC Information function.

Scheme 28

The powertrain control module (PCM) uses the cooling fan speed signal in order to determine the actual fan speed in relation to the desired fan speed. The PCM uses the cooling fan speed signal in order to reduce the cooling fan noise and in order to maintain the powertrain cooling requirements. The PCM supplies power and ground to the clutch hall effect sensor of the cooling fan clutch. The hall effect sensor returns a signal pulse through the speed signal circuit in response to the reluctor track, which is located inside the fan clutch. If during operation, the PCM detects a loss of the cooling fan speed signal, DTC P1481 will set.

1. The engine is running.
2. System voltage is greater than 8.5 volts.

1. The PCM has detected a loss of cooling fan speed signal.
2. The above condition is present for at least 11 seconds.

1. The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM will store the condition as Freeze Frame/Failure Records data.
3. The PCM commands the cooling fan clutch to 100%

1. The PCM turns OFF the malfunction indicator lamp (MIL) after the third consecutive trip that the diagnostic test has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. Clear the DTC by using the Clear DTC Information function of the scan tool.

1. 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.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. Disconnect the harness connector of the cooling fan clutch from the shroud. Inspect the exposed wires between the harness connector and the tubing.
4. Inspect the cooling fan clutch harness in order to ensure that the clutch supply voltage circuit is not shorted to the following circuits: The 5-volt reference circuit. The cooling fan speed signal circuit. The low reference circuit.
5. DTC P1481 will set if the engine is started without the drive belt ON.

The powertrain control module (PCM) sends a pulse width modulation (PWM) signal of 0-12 volts via the cooling fan clutch control circuit to the cooling fan relay. The PCM uses this PWM to control the position of the oil control valve located inside the cooling fan clutch. If during operation, the PCM detects an improper circuit condition on the cooling fan clutch control circuit DTC P1482 will set.

System voltage is greater than 8.5 volts.

1. An improper voltage level has been detected on the cooling fan clutch control circuit.
2. The above condition is present for at least 6 seconds.

1. The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM stores the conditions present when the DTC sets as Freeze Frame/Failure Records data.
3. The PCM commands the cooling fan clutch to 100%.

1. The PCM turns OFF the malfunction indicator lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using the scan tool Clear DTC Information function.

1. 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.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. Disconnect the harness connector of the cooling fan clutch from the shroud. Inspect the exposed wires between the harness connector and the tubing.

The cooling fan relay sends a pulse width modulation (PWM) signal of 12-14 volts to the cooling fan clutch through the cooling fan clutch supply voltage circuit. The powertrain control module (PCM) uses this PWM signal in order to control the speed of the cooling fan clutch. The signal controls the position of the oil control valve inside the cooling fan clutch. If the cooling fan RPM is different than the PCM is expecting, DTC P1484 will set. The actual cooling fan RPM vs the desired cooling fan RPM is not always exactly the same. There can be up to an 800-RPM difference.

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 P1481 and P1482 are not set.
5. The engine speed is less than 3200 RPM.
6. The engine speed is not changing more than 250 RPM for 5 seconds.
7. Fan command is greater than 0%.

1. The maximum allowable error of 1000 RPM in the cooling fan speed occurs for 100 seconds.
2. The PCM detects that the cooling fan clutch is locked up.

1. The Reduced Engine Power indicator illuminates only if the PCM detects that the cooling fan clutch is locked up.
2. The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
3. The PCM will store the conditions as Freeze Frame/Failure Records data.
4. The PCM commands the cooling fan clutch to 100%.

1. Use the Clear DTC Information function on the scan tool.
2. Perform an ignition key cycle.

The PCM turns OFF the MIL after the third consecutive trip that the diagnostic test has run and passed.

The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

1. 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.
2. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.
3. Disconnect the harness connector of the cooling fan clutch from the shroud. Inspect the exposed wires between the harness connector and the tubing.
4. If DTCs P1484 and P0113 are set, and the weather conditions are cold, the cooling fan code may be false. Clear DTC P1484, and after an IAT sensor check, allow the DTC to reset.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the Cooling System. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
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-188500-S26620016842005090300000)
2. «ENGINE OVERHEATING»(ref-188500-S08993684442005090300000)
3. «LOSS OF COOLANT»(ref-188500-S21349022862005090300000)
4. «THERMOSTAT DIAGNOSIS»(ref-188500-S27803325392005090300000)
5. «COOLANT HEATER INOPERATIVE»(ref-188500-S38862513742005090300000)
6. «ENGINE FAILS TO REACH NORMAL OPERATING TEMPERATURE»(ref-188500-S05075943722005090300000)
7. «EXCESSIVE FAN NOISE»(ref-188500-S00326938672005090300000)

Scheme 29

Scheme 30

Scheme 31

Scheme 32

Scheme 33

Scheme 34

Scheme 35

Scheme 36

Scheme 37

Scheme 38

Scheme 39

Pressure Cap Testing

Tools Required

1. J 24460-01 Cooling System Pressure Tester
2. J 42401 Radiator Cap / Surge Tank Test Adapter

Scheme 40

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.
4. 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. 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.

Cooling System Leak Testing

Tools Required

J 24460-01 Cooling System Pressure Tester

Scheme 41

1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «PRESSURE CAP TESTING»(ref-188500-S10140180442005090300000) .
3. Wash the pressure cap mating surface with water.
4. Use the J 24460-01 in order to apply pressure to the cooling system. 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.

The electro-viscous clutch is controlled by the 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 a hydraulic fluid. There is two chambers for the fluid, these two 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.

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% command with the engine at 2000 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 2000 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 AND POOR CONNECTIONS»(ref-188866-S12601397672005090500000) in Wiring Systems.