Engine Cooling System: Diagnosis Pontiac Sunfire 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 Class 2 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

ECT: 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 Powertrain Control Module (PCM) applies 5 volts to the ECT sensor signal circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold and the internal resistance is high, the PCM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms and the internal resistance decreases, the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.

FC Relay 1 Command: The fan control (FC) relay is commanded by the PCM. FC Relay 1 displays the command as ON or OFF.

Low Coolant Lamp: The scan tool displays ON or OFF. The state of the Low Coolant indicator as commanded by the IPC. The IPC receives a class 2 message from the BCM indicating the coolant level.

Low Coolant Level: The scan tool displays ON or OFF. The state of the low coolant level switch.

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Circuit Description

Battery positive voltage is supplied to the cooling fan relay from the cooling fan fuse. The powertrain control module (PCM) controls the cooling fan relay by grounding the cooling fan relay control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a component off, 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 will monitor the control circuit for the following

1. A short to ground
2. A short to voltage
3. An open circuit
4. An open relay coil
5. An internally shorted or excessively low resistance relay coil.

When the PCM detects any of the above conditions, the DTC will set and the affected driver will be disabled.

Conditions for Running the DTC

1. The ignition is ON.
2. The battery voltage is more than 9.5 volts.

Conditions for Setting the DTC

1. The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
2. The condition must be present for a minimum of 6.25 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 will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

1. The PCM will turn OFF the MIL during the third consecutive trip in which 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.

Diagnostic Aids

1. If the condition is not present, refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-170169) .
2. Review the Freeze/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.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the Cooling System.
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. «Low Engine Coolant Indicator Always On»(ref-174538-S30238240852005061600000)
2. «Cooling Fan Always On»(ref-174538-S11191569442005061600000)
3. «Cooling Fan Inoperative»(ref-174538-S40683097402005061600000)
4. «Engine Overheating»(ref-174538-S42702025512005061600000)
5. «Loss of Coolant»(ref-174538-S17528025932005061600000)
6. «Thermostat Diagnosis»(ref-174538-S36424209182005061600000)
7. «Coolant Heater Inoperative»(ref-174538-S38762685942005061600000)
8. «Engine Fails To Reach Normal Operating Temperature»(ref-174538-S37068755082005061600000)

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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 J 24460-01 and J 42401 in order to test the pressure cap for the following conditions: Pressure release when 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.
4. Replace the pressure cap if either of the following conditions is true: 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

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

Scheme 29

1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(ref-174538-S01577552592005040600000) .
3. Wash the pressure cap sealing surface with water.
4. Use J 24460-01 and J 42401 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.
5. Observe the pressure gage for any pressure loss.
6. Repair any leaks as required.