GM Service Manual Online
For 1990-2009 cars only
A/C Clutch - Actual: The scan tool displays On/Off. The HVAC control module displays On when the engine control module (ECM) transmits a class 2 message that the A/C compressor clutch relay is energized.

A/C Clutch - Desired: The scan tool displays Yes/No. The scan tool displays Yes when the HVAC control module determines that conditions for compressor clutch engagement are present.

A/C High Side Pressure Sensor: The scan tool displays 0-3450 kPa (0-500 psi). The voltage applied to the ECM input from the A/C refrigerant pressure sensor is converted to a pressure value.

A/C High Side Pressure Sensor: Scan tool displays 0-5 V. The voltage applied to the ECM input for the A/C refrigerant pressure sensor.

A/C Pressure: The scan tool displays 0-3450 kPa (0-500 psi). The voltage applied to the ECM input from the A/C refrigerant pressure sensor is converted to a pressure value and transmitted in a class 2 message to the HVAC control module.

A/C Relay Command: The scan tool displays On/Off. The scan tool displays the control decision for the compressor clutch relay output as determined by the ECM.

A/C Request Signal: The scan tool displays Yes/No. The scan tool displays Yes when the ECM receives a class 2 message from the HVAC control module to engage the A/C compressor clutch. The scan tool displays No when the ECM receives a class 2 message from the HVAC control module to disengage the A/C compressor clutch.

Commanded Blower: The scan tool displays 0-100%. The scan tool displays the control decision for the blower motor speed as determined by the HVAC control module. The scan tool displays 100% when the blower motor is commanded to maximum speed. The scan tool displays 0% when the blower motor is commanded OFF.

Coolant Temperature: The scan tool displays -39 to +140°C (-38 to +284°F). The voltage applied to the ECM input from the engine coolant temperature sensor is converted to a temperature value and transmitted in a class 2 message to the HVAC control module.

Driver Temp Dr. Actual: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the driver air temperature door position input of the HVAC control module.

Driver Temp Dr. Commanded: The scan tool displays 0-255 counts (0-5.00V). The desired position of the driver air temperature actuator as determined by the HVAC control module.

Driver Solar Sensor: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the driver sunload input of the HVAC control module.

Driver Sunload: The scan tool displays 0-2000 wm/m2. The voltage applied to the driver sunload input of the HVAC control module converted to light intensity units.

ECT Sensor: The scan tool displays -39 to +140°C (-38 to +284°F). The voltage applied to the ECM input from the engine coolant temperature sensor is converted to a temperature value.

ECT Sensor: The scan tool displays -39 to +140°C (-38 to +284°F). The voltage applied to the ECM input from the engine coolant temperature sensor is converted to a temperature value.

Evaporator Temp: The scan tool displays -39 to +140°C (-38 to +284°F). The voltage applied to the HVAC control module input from the evaporator temperature sensor is converted to a temperature value.

Evaporator Temp: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the HVAC control module input for the evaporator temperature sensor.

Htr./Def./A/C Dr. Actual: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the mode door position input of the HVAC control module.

Htr./Def./A/C Dr. Commanded: The scan tool displays 0-255 counts (0-5.00V). The desired position of the mode actuator as determined by the HVAC control module.

Inside Air Temp.: The scan tool displays -40 to +215°C (-40 to +419°F). The voltage applied to the HVAC control module input for the inside air temperature sensor is converted to a temperature value.

Inside Air Temp.: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the HVAC control module input for the inside air temperature sensor.

Low Coolant Status: The scan tool displays OK/Low. The filtered state of the low coolant switch.

Low Coolant Switch: The scan tool displays Open/Closed. The actual state of the low coolant switch.

Outside Air Temp: The scan tool displays -40 to +215°C (-40 to +419°F). The current value of the ambient air temperature display on the HVAC control module.

Outside Air Temp: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the HVAC control module input for the outside air temperature sensor.

Passenger Solar Sensor: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the passenger sunload input of the HVAC control module.

Passenger Sunload: The scan tool displays 0-2000 w/m2. The voltage applied to the driver sunload input of the HVAC control module converted to light intensity units.

Passenger Temp Dr. Actual: The scan tool displays 0-255 counts (0-5.00V). The voltage applied to the passenger air temperature door position input of the HVAC control module.

Passenger Temp Dr. Commanded: The scan tool displays 0-255 counts (0-5.00V). The desired position of the passenger air temperature actuator as determined by the HVAC control module.

Pressure Sensor: The scan tool displays OK/Failed. The state of the A/C refrigerant pressure sensor and circuitry.

A/C Off (1-8) History Records: The scan tool displays the reason for A/C Off.

Turning off the A/C makes the throttle fully open: This parameter displays whether the A/C is off in order to fully open the throttle. The scan tool displays Yes if the A/C is detected off. The scan tool displays No if the A/C is not detected off.

A/C Pressure Disabled: This parameter displays the state of the A/C pressure driver. The scan tool displays Yes if the A/C pressure is detected disabled. The scan tool displays No if the A/C pressure is not detected disabled.

A/C Relay Circuit Status: This parameter displays the state of A/C relay control circuit under the control module command.

5V Reference Voltage 1: This parameter displays the perceived voltage of the 5V reference voltage circuit 1 of the control module. The scan tool displays the high value under the higher voltage. The scan tool displays the low value under the lower voltage.

5V Reference Voltage 2: This parameter displays the perceived voltage of the 5V reference voltage circuit 2 of the control module. The scan tool displays the high value under the higher voltage. The scan tool displays the low value under the lower voltage.

5V Reference Voltage 1 or 2 Circuit Status: This parameter displays the diagnostic state of the 5V reference voltage circuit output driver. The scan tool displays OK/Failed. OK No circuit failure has been detected in the current test. Fault: Short or open circuit/component, at this time there is no electrical connection between this circuit/component and the control module. Engine Load: This parameter displays the percentage of the engine load calculated according to engine sensors input of the control module. The scan tool displays low percentage if the engine load is too low or there is no load when idling. The scan tool displays high percentage when the engine is at a high speed and carrying a heavy load.

The Calculated Engine Oil Temperature: This parameter displays the engine oil temperature calculated by the control module according to the engine oil temperature sensor signal. The engine oil temperature sensor has a certain range; it displays the low value when the engine oil temperature is low; it displays the high value when the oil temperature is high.

Engine Oil Temperature Sensor: This parameter displays the engine oil temperature calculated by the control module according to the engine oil temperature sensor signal. The engine oil temperature sensor has a certain range; it displays the low value when the engine oil temperature is low; it displays the high value when the oil temperature is high.

Engine Run Time: This parameter displays the run time after the engine starts. The scan tool displays the time in hour, minute and second. The engine run time will return to zero when the engine stops.

Engine Speed: This parameter displays the crankshaft speed calculated by the control module according to the crankshaft position (CKP). The scan tool displays the high value when the engine speed is high; the scan tool displays the low value when the engine speed is low.

Hot Open Loop: This parameter indicates the fuel transmission system status. The scan tool displays Active if the fuel system operates under an open loop due to the temperature. The scan tool displays Inactive if the fuel system operates normally.

Intake Air Temperature (IAT) Sensor: This parameter is the intake air temperature of the engine calculated by the control module according to intake air temperature sensor input. The scan tool displays the low value when the air temperature is low; the scan tool displays the high value when the air temperature is high.

Ignition 1 Signal: This parameter displays the voltage measured in the ignition 1 circuit of the control module. The voltage is applied to the control module when the ignition switch is on the ignition 1 position. The scan tool displays the low value under the low voltage. The scan tool displays the high value under the high voltage.

Knock Retard: This parameter indicates the ignition advance subtracted from the ignition control (IC) ignition advance by the control module in response to the signal from the knock sensor.

Spark: This parameter displays the spark timing of the control module command on the ignition control circuit. The scan tool displays a negative value if the spark timing is Before Top Dead Center (BTDC) or spark advance; the scan tool displays a positive value if the spark timing is After Top Dead Center (ATDC) or spark retard. Because ignition control module sets the ignition advance to the BTDC fixed value under the bypass mode operations, when the power system control module commands ignition control mode, the displayed ignition advance indicates the actual ignition timing.

Engine Coolant Temperature at Start: This parameter indicates the engine coolant temperature at start calculated by the control module according to the signal from engine coolant temperature sensor. The scan tool displays the high value when the engine warms up; the scan tool displays the low value when the engine is cold.

Calculated Engine Coolant Temperature - Closed Loop Fuel Control: The scan tool displays -39 to +140°C (-38 to +284°F) under the closed loop fuel control. The voltage applied by the sensor to engine control module input is converted to the temperature value.

Calculated Engine Coolant Temperature - Thermostat Diagnosis: The scan tool displays -39 to +140°C (-38 to +284°F) under the thermostat diagnosis. The voltage applied by the sensor to engine control module input is converted to the temperature value.

Intake Air Temperature: This parameter indicates the intake air temperature calculated by the control module according to the signal from the intake air temperature sensor. The scan tool displays the high value when the engine hood temperature is high; the scan tool displays the low value when the engine hood temperature is low.

Transmission Oil Temperature Sensor: This parameter displays the transmission oil temperature calculated by the control module according to the transmission oil temperature sensor signal. The engine oil temperature sensor has a certain range; it displays the low value when the engine oil temperature is low; it displays the high value when the oil temperature is high.

Total Knock Retard: This parameter indicates the ignition spark timing retard which is caused by all the control systems and monitored by the module. The scan tool displays the high value under the extreme conditions (such as high temperature and anti-lock braking). The scan tool displays the low value under a light load driving.

Vehicle Speed Sensor: This parameter indicates the vehicle speed calculated by the control module according to the signal from vehicle speed sensor (VSS). The scan tool displays the high value at a high speed; the scan tool displays the low value at a low speed.

Capacity Efficiency: This parameter indicates the engine capacity efficiency calculated by the control module.