Engine Cooling System: Diagnosis Chevrolet Suburban X

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 module(s) which command the system.
2. The ability of the control module(s) 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

Check Coolant Temp - Range: ON/OFF: This output refers to the commanded state of the Check Coolant Temp message located in the message center. The message will be added to the message center display based on the engine coolant temperature that is sent to the Instrument Cluster as a class 2 message from the PCM. If the engine temperature is greater than 121°C (250°F) the message will be added to the message center, unless the Check Engine Temp message has been added to the message center, and removed when the engine temperature is less than 118°C (245°F).

Check Engine Temp - Range: ON/OFF: This output refers to the commanded state of the Check Engine Temp message located in the message center. The message will be added to the message center display based on the engine coolant temperature that is sent to the Instrument Cluster as a class 2 message from the PCM. If the engine temperature is greater than 128°C (262°F) the message will be added to the message center and removed when the engine temperature is less than 125°C (257°F)

Coolant Level Switch - Range: Low/OK: This parameter indicates when the engine coolant level is low. The scan tool displays Low when the PCM detects the engine coolant level switch is open.

ECT - Range: -40°C to +150°C (-40°F to +302°F): The PCM applies 5.0 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as the engine temperature changes. When the sensor is cold (internal resistance high), the PCM senses a high signal voltage and interprets the voltage as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.

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).

Low Coolant - Range: ON/OFF: This output refers to the command state of the Low Coolant message located in the message center. ON is displayed when the Instrument Cluster is commanding the Low Coolant message ON. OFF is displayed when the Instrument Cluster is not commanding the Low Coolant message ON. The Instrument Cluster will display the Low Coolant message when the Instrument Cluster receives a class 2 serial data message from the PCM.

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.

Reduced Engine Power - Range: ON/OFF: This output refers to the commanded state of the Reduced Engine Power message located in the message center. On is displayed when the Instrument Cluster is commanding the Reduced Engine Power message ON. OFF is displayed when the Instrument Cluster is not commanding the Reduced Engine Power message ON. The Instrument Cluster will display the Reduced Engine Power message when the Instrument Cluster receives a class 2 serial data message from the PCM when the engine temperature reaches 132°C (270°F).

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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

1. DTCs P0117, P0118, P1114, and P1115 are not active.
2. 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

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.

Scheme 14

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.

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

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.
3. 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

1. Engine Overheated Indicator Always On, See «Engine Overheated Indicator Always On»(ref-180280-S36875708862005092600000)
2. Engine Coolant Temperature Indicator Always On, See «Engine Coolant Temperature Indicator Always On»(ref-180280-S17408915602005092600000)
3. Low Engine Coolant Indicator Always On, See «Low Engine Coolant Indicator Always On»(ref-180280-S42529577702005092600000)
4. Coolant Heater Inoperative, See «Coolant Heater Inoperative»(ref-180280-S01773564422005092600000)
5. Engine Overheating, See «Engine Overheating Diagnostic»(ref-180280-S06735360262005092600000)
6. Loss of Coolant, See «Loss Of Coolant Diagnostic»(ref-180280-S18183848112005092600000)
7. «THERMOSTAT DIAGNOSIS»(ref-180280-S02910672202005072500000)
8. Engine Fails To Reach Normal Operating Temperature, See «Engine Fails To Reach Normal Operating Temperature»(ref-180280-S02932847372005092600000)
9. Fan Clutch Diagnosis, See «Fan Clutch»(ref-180280-S13299930812005092600000)

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Thermostat Diagnosis

Tools Required

J 24731 Tempil-Stick

Use one of the following procedures in testing for a malfunctioning thermostat.

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.

1. 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. J24731 -206 tempil stick melts at 97°C (206°F). The thermostat should be fully open.
2. 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

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1. Completely submerge the thermostat in the glycol solution. The solution should be 11°C (22°F) above the temperature indicated on the thermostat valve.
2. 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

1. Completely submerge the thermostat in a glycol solution. The solution should be 6°C (10°F) below the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.

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Pressure Cap Testing

Tools required

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

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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

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1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «PRESSURE CAP TESTING»(ref-180280-S31444667012005072500000) .
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 gage for any pressure loss.
6. Repair any leaks as required.

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