Engine Cooling System: Diagnosis Pontiac Vibe I

Diagnostic Starting Point - Engine Cooling

Begin the system diagnosis by reviewing the COOLING SYSTEM DESCRIPTION AND OPERATION . Reviewing the Description and Operation information will help you determine the correct symptom diagnostic procedure when a malfunction exists. Reviewing the Description and Operation information will also help you determine if the condition described by the customer is normal operation. Refer to SYMPTOMS - ENGINE COOLING in order to identify the correct procedure for diagnosing the system and where the procedure is located.

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Scan Tool Data Definitions

AC Clutch: The parameter indicates On whenever the powertrain control module (PCM) energizes the A/C compressor clutch relay. Engaging the A/C compressor clutch relay will also engage the cooling fan at low speed.

AC Request Signal: This parameter indicates whether the A/C switch on the instrument panel (IP) has been selected.

ECT Sensor: The scan tool range is -40 to +140°C (-40 to +284°F). The engine coolant temperature (ECT) sensor is a thermistor which changes internal resistance as the temperature changes. When the sensor is cold, internal resistance high, the powertrain control module (PCM) monitors 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.

Symptoms - Engine Cooling

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the 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 all related ground points for being clean and tight.

Symptom List

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

1. «COOLING FAN ALWAYS ON»(ref-186684-S19657013172005083100000)
2. «COOLING FAN INOPERATIVE (INOPERATIVE)»(ref-186684-S02703818042005083100000) or «COOLING FAN INOPERATIVE (INOPERATIVE IN LOW SPEED)»(ref-186684-S38826425462005083100000) or «COOLING FAN INOPERATIVE (INOPERATIVE IN HIGH SPEED)»(ref-186684-S06670961662005083100000) or «COOLING FAN INOPERATIVE (LOW SPEED OPERATES IN HIGH SPEED)»(ref-186684-S34068531742005083100000)
3. «ENGINE OVERHEATING»(ref-186684-S37893936262005083100000)
4. «LOSS OF COOLANT»(ref-186684-S05971693572005083100000)
5. «THERMOSTAT DIAGNOSIS»(ref-186684-S40879554262005083100000)
6. «ENGINE FAILS TO REACH NORMAL OPERATING TEMPERATURE»(ref-186684-S22566499212005083100000)

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1. Remove the thermostat from the vehicle in order to perform the thermostat test. Refer to «THERMOSTAT REPLACEMENT»(ref-186684-S00324070002005083100000) .
2. Fill a pan with a 50/50 mixture of ethylene glycol and water. Suspend the thermostat (1) and a thermometer (3) in the pan. Do not place the thermostat (or thermometer) on the bottom of the pan. The concentration of heat is uneven at the bottom of the pan. This condition may cause inaccurate temperature measurements.
3. Place the pan on a burner (2).
4. Heat the solution.
5. Use a thermometer (3) in order to measure the temperature of the solution.
6. Ensure that the following specifications exist: The thermostat valve opening temperature is within 80°C to 84°C (176°F to 183°F). The valve lift is 8 mm (0.31 in) or more at 95°C (203°F). If the above specifications are not met, replace the thermostat (1).
7. Verify that the valve spring is tight when the thermostat is fully closed. Replace the thermostat if the spring is not tight.

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