GM Service Manual Online
For 1990-2009 cars only
3X Crank Sensor: The scan tool range is 0-9999. Displays engine speed.

24X Crank Sensor: The scan tool range is 0 to approximately 1,600 RPM. Displays the engine speed calculated from the 24X reference signal powertrain control module (PCM) input should nearly match ENGINE SPEED up to approximately 1,600 RPM limit.

A/C High Side Pressure Sensor: The scan tool displays 0-459 kPa. Represents the A/C refrigerant pressure sensor signal. The amount of pressure indicates the amount of load that the A/C compressor is placing on the engine. The PCM uses this information to adjust idle and to control the cooling fans.

A/C OFF For WOT: The scan tool displays YES or NO. Yes displayed indicates that the PCM has commanded the A/C compressor clutch relay OFF because the throttle position (TP) is more than the threshold of 90 percent .

A/C Pressure Disable: The scan tool displays YES or NO. YES displayed indicates that the powertrain control module (PCM) is monitoring an A/C refrigerant pressure signal voltage which is too high or too low to allow the A/C compressor clutch to engage.

A/C Relay Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

A/C Relay command : The scan tool displays ON or OFF. Represents the PCM commanded state of the A/C compressor clutch relay driver circuit. The A/C compressor clutch should be engaged when commanded A/C displays ON

A/C Request Signal: The scan tool displays YES or NO. Indicates the state of the A/C request input circuit from the HVAC controls. The PCM uses the A/C request signal to determine whether A/C compressor operation is being requested.

Air Fuel Ratio: The scan tool range is 0.0-25.5. Air fuel ratio indicates the PCM commanded value. In closed loop, air fuel ratio should normally be around 14.2-14.7. A lower air fuel ratio indicates a richer commanded mixture, which may be seen during Power Enrichment or three-way catalytic converter (TWC) Protection modes. A higher air fuel ratio indicates a leaner commanded mixture. This can be seen during Decel Fuel Mode.

BARO: The scan tool range is 10-105 kPa/0.00-5.00 volts. The barometric pressure (BARO) reading is determined from the manifold absolute pressure (MAP) sensor signal monitored during key up and wide-open throttle (WOT) conditions. The barometric pressure is used to compensate for altitude differences.

CMP Sensor Signal Present: The scan tool displays YES or NO. Indicates whether or not the correct CAM signal has been received by the PCM during the last six 3X reference pulses. NO displayed indicates no CAM signal received. A toggling display indicates an intermittent CAM signal.

Crank Request Signal: The scan tool displays YES or NO. Yes is displayed when the key is in crank position.

Cruise Control Active: The scan tool displays YES or NO. Represents the state of the Cruise Status Input from the cruise control module. CRUISE ENGAGED should not display YES unless the vehicle is operating in a cruise control mode.

Cruise Inhibit Reason: The scan tool displays various terms related to cruise control operation.

Cruise Inhibit Signal Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

Cruise Inhibit Signal Command: The scan tool displays ON or OFF ON displayed indicates that the PCM is commanding the cruise control module to inhibit cruise control operation. Should display ON at idle.

Current Gear: The scan tool displays numbers 1, 2, 3, or 4. The PCM looks at trans range position and the gear commanded by the PCM. The actual forward gear that the transaxle is in will be the lower of the two because the manual valve can override the PCM commanded gear.

Cycles of Misfire Data: The scan tool range is 0-99 counts. Indicates the total number of cylinder firing events that were detected as being misfires during the last 200 crankshaft revolution sample period.

Cylinder 1 through 6 Injector Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

Cylinder 1 through 6 Injector Circuit History: The scan tool displays Fault or OK This parameter saves the state of the driver circuit for this device.

Decel Fuel Cutoff: The scan tool displays ACTIVE or INACTIVE. ACTIVE displayed indicates that the PCM has detected conditions appropriate to operate in Deceleration Fuel Mode. The PCM will command deceleration fuel mode when a sudden decrease in throttle position has been detected while the vehicle is traveling over 40.23 km/h (25 mph). While in Deceleration Fuel mode, the PCM will decrease the amount of fuel delivered by entering Open Loop and decreasing the injector pulse width.

Desired EGR Position: scan tool range is 0-100 percent. Represents the exhaust gas recirculation (EGR) pintle position that the PCM is commanding. Desired EGR position should stay close to actual EGR position.

Desired Idle Speed: The scan tool range is 0-3187 RPM. The idle speed that is commanded by the PCM. The PCM will compensate for various engine loads based on engine coolant temperature (ECT) to keep the engine at the desired speed.

Driver Module 1 Status: The scan tool displays Enabled or Disabled. This parameter indicates the state of the driver circuit for this device.

Driver Module 2 Status: The scan tool displays Enabled or Disabled. This parameter indicates the state of the driver circuit for this device.

Driver Module 3 Status: The scan tool displays Enabled or Disabled. This parameter indicates the state of the driver circuit for this device.

Driver Module 4 Status: The scan tool displays Enabled or Disabled. This parameter indicates the state of the driver circuit for this device.

ECT Sensor: The scan tool range is -40 to +151°C (-40 to +304°F). The engine coolant temperature (ECT) sensor is mounted in the coolant stream and sends engine temperature information to the PCM.

EGR Flow Test Count: The scan tool range is 0-255. Indicates the number of exhaust gas recirculation (EGR) flow test samples collected during the current ignition cycle.

EGR Learned Minimum Position: The scan tool range is 0.0-5.0 volts. Represents the learned voltage that the PCM uses to determine whether or not the EGR valve is fully closed.

EGR Position Sensor: The scan tool range is 0-100 percent or 0.00-5.00 volts. Represents the actual position of the EGR pintle in percent. 0 percent or 0 Volts displayed indicates EGR valve closed.

EGR Position Variance: The scan tool range is 0-100 percent. Indicates the difference between desired EGR position and actual EGR position currently being monitored by the PCM.

EGR Solenoid Command: The scan tool range is 0-100 percent. Displays the pulse width modulated (BWM) duty cycle that the PCM is applying to the EGR solenoid. 0 percent indicates no EGR is commanded.

Engine Load: The scan tool range is 0-100 percent. Engine load is calculated by the PCM from engine speed and mass air flow (MAF) sensor readings. Engine load should increase with an increase in RPM or air flow.

Engine Oil Level Switch: The scan tool displays OK or Not OK. Indicates the oil level as determined by the engine oil level sensor.

Engine Oil Life Remaining: The scan tool range is 0-100 percent. This display represents the engine oil life index that is calculated and maintained by the PCM.

Engine Oil Pressure Switch: The scan tool displays OK or Not OK. This parameter displays whether or not sufficient engine oil pressure is present.

Engine Run Time: The scan tool range is 00:00:00-99:99:99 Hrs:Min:Sec. Indicates the time elapsed since the engine was started. If the engine is stopped, ENGINE RUN TIME will be reset to 00:00:00.

Engine Speed: The scan tool range is 0-9999 RPM. Engine speed is computed by the PCM from the 3X reference input. The engine speed should remain close to desired idle under various engine loads with engine idling.

EVAP Fault History: The scan tool displays No Fault, Excess Vacuum, Purge Valve Leak, Small Leak or Weak Vacuum. This parameter displays the result of the evaporative emission (EVAP) system diagnostic.

EVAP Purge Solenoid Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

EVAP Purge Solenoid Command: The scan tool range is 0-100 percent. Represents the PCM commanded pulse width modulated (PWM) duty cycle of the EVAP purge solenoid valve. 0 percent displayed indicates no purge. 100 percent displayed indicates full purge.

Evap Test Abort Reason: The scan tool displays Not Aborted, Lost Enable, Small Leak, Vehicle Not at Rest. Provides additional information relative to the EVAP Test Result parameter.

EVAP Test Result: The scan tool displays No Results, Passed, Aborted, Fail DTC P0440, Fail DTC P0442, Fail DTC P0446, Fail DTC 1441. This information can be used to check system operation. Operate the vehicle within the conditions required to enable the diagnostic, refer to the EVAP DTCs supporting text. This parameter displays the results of the EVAP system diagnostic tests.

EVAP Test State: The scan tool displays Test Completed, Test Running, Wait for Purge . Indicates the current status of the EVAP diagnostic routine.

EVAP Vent Solenoid Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

EVAP Vent Solenoid Command: The scan tool displays Venting or Closed. This parameter indicates the commanded state of the driver circuit for this device.

FC Relay 1 Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

FC Relay 1 Command: If applicable, the scan tool displays ON or OFF. Represents the PCM commanded state of the low speed and high speed fan relay drivers.

FC Relay 2 and 3 Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

FC Relay 2 and 3 Command: If applicable, the scan tool displays ON or OFF. Represents the PCM commanded state of the low speed and high speed fan relay drivers.

Fuel Level Sensor: The scan tool displays 0-5.00 volts. The PCM converts the signal voltage to a fuel level value. The scan tool displays close to 0.8 volts for an empty tank, and close to 2.5 volts for a full tank.

Fuel Pump Relay Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

Fuel Pump Relay Circuit History Status: The scan tool displays Fault or OK This parameter saves the state of the driver circuit for this device.

Fuel Pump Relay Command: The scan tool displays ON or OFF. Indicates the PCM commanded state of the fuel pump relay driver circuit.

Fuel Tank Level Remaining: The scan tool displays 0-100 percent The scan tool displays in percentage the amount of fuel remaining in the fuel tank.

Fuel Tank Pressure Sensor: The scan tool displays 0-5 volts or -17.5 to +7.5 in of H2O. Fuel tank pressure is used extensively for EVAP purge control and EVAP system diagnostics.

Fuel Trim Cell: The scan tool displays cell#. Fuel trim cell is dependent upon engine speed and mass air flow (MAF) sensor readings. A plot of RPM vs. MAF is divided into 10 cells. Fuel trim cell indicates which cell is currently active.

Fuel Trim Learn: The scan tool displays ENABLED or DISABLED. When conditions are appropriate for enabling long term fuel trim corrections, FUEL TRIM LEARN will display Enabled. This indicates that the long term fuel trim is responding to short term fuel trim. If the Fuel Trim Learn displays Disabled, long term fuel trim will not respond to changes in short term fuel trim.

Generator F. Terminal Signal: The scan tool displays %. This parameter indicates the pulse width of the voltage regulator generator field control circuit, a high value indicates high electrical load.

Generator L Terminal Signal Command: The scan tool displays ON or OFF. ON displayed indicates that the PCM has commanded the generator ON.

HO2S 1: The scan tool range is 0-1132 mV. Represents the fuel control exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 10 mV, lean exhaust, and 1000 mV, rich exhaust, while operating in Closed Loop.

HO2S 2: The scan tool range is 0-1132 mV. Represents the catalyst monitor exhaust oxygen sensor output voltage. If the catalyst is operating efficiently, the heated oxygen sensor (HO2S) 1 signal will be far more active than that produced by the HO2S 2 sensor.

HO2S 1 Heater Command: The scan tool displays ON or OFF. Displays the PCM commanded state of the O2 heater.

IAC Position: The range is 0-255 counts. Displays the commanded position of the idle air control (IAC) pintle in counts. A larger number of counts means that more air is being commanded through the idle air passage. Idle air control position should respond fairly quickly to changes in engine load to maintain desired idle RPM.

IAT Sensor: The scan tool range is -40 to +151°C (-40 to +304°F). The PCM converts the resistance of the intake air temperature sensor to degrees.

Ignition 1 Signal: The scan tool displays 0-25.5 volts The Ignition 1 represents the system voltage measured by the PCM at its ignition feed.

Ignition Mode: The scan tool displays Bypass/IC. Bypass indicates the ignition control (IC) module is keeping the spark advance at a fixed 10 degrees before top dead center (BTDC). Ignition control (IC) indicates that the PCM has signaled the ignition module that the PCM is going to control the spark advance.

Injector PWM: The scan tool range is 0-1,000 ms. Indicates the amount of time the PCM is commanding each injector ON during each engine cycle. A longer injector pulse width will cause more fuel to be delivered. Injector pulse width should increase with increased engine load.

Knock Retard: The scan tool range is 0.0-25.5 degrees. Indicates the amount of timing the PCM is removing from IC spark advance in response to the signal from the knock sensors (KS).

Long Term FT: The scan tool range is -23 to +16 percent. Long term fuel trim is derived from the short term fuel trim value and represents a long term correction of fuel delivery. A value of 0 percent indicates that fuel delivery requires no compensation to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0 percent indicates that the fuel system is rich and fuel delivery is being reduced. A positive value significantly more than 0 percent indicates that a lean condition exists and the PCM is compensating by adding fuel.

Loop Status: The scan tool displays OPEN or CLOSED. Closed Loop indicates that the PCM is controlling fuel delivery according to oxygen sensor voltage. In Open Loop, the PCM ignores the oxygen sensor (O2S) voltage and bases the amount of fuel to be delivered on throttle position (TP) sensor, engine coolant temperature (ECT), and mass air flow (MAF) sensor inputs only.

MAF Sensor: The scan tool range is 0.0-512 g/s. Mass air flow (MAF) is the MAF input frequency converted to grams of air per second. This indicates the amount of air entering the engine.

MAF Sensor: The scan tool range is 0-32,000 Hz. The mass air flow sensor input signal to the PCM is a frequency which varies from around 3,000 Hz at idle to above 7,000 Hz at wide-open throttle (WOT). The PCM converts this frequency signal to grams per second to be displayed as mass air flow.

MAP Sensor: The scan tool range is 10-105 kPa (0.00- 4.97 volts). The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure. As intake manifold pressure increases, intake vacuum decreases.

MIL Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

MIL Command: The scan tool displays ON or OFF. Indicates the PCM commanded state of the malfunction indicator lamp (MIL).

Misfire Current Cyl #1 / Misfire Current Cyl #2 / Misfire Current Cyl #3 / Misfire Current Cyl #4 / Misfire Current Cyl #5 / Misfire Current Cyl #6: The scan tool range is 0-198 counts. The misfire current counters indicate the number of cylinder firing events detected as possible misfires on each cylinder during the last 200 crankshaft revolutions. The number that the counters display are twice the actual number of misfire events detected. The counters may normally display some activity, but the activity should be very low and nearly equal for all the cylinders.

Misfire History Cyl #1 / Misfire History Cyl #2 / Misfire History Cyl #3 / Misfire History Cyl #4 / Misfire History Cyl #5 / Misfire History Cyl #6: The scan tool range is 0-65535 counts. The misfire history counters indicate the total level of misfire that has been detected on each cylinder. The number that the counters display are twice the actual number of misfire events detected. The misfire history counters will not update or show any activity until a misfire DTC P0300 has become active. The misfire history counters will be updated every time a 200 crankshaft revolution misfire test failure is detected.

Number of DTCs: The scan tool displays number This parameter displays the quantity of active DTCs.

O2 Heater Current: The scan tool displays Amps The scan tool displays HO2S Heater Current in amps. This parameter displays the current draw of the HO2S 1 heater only. Typically, the HO2S heater current stabilizes at about 0.50-0.60 amps after operating temperature is reached. Initial current draw is slightly higher.

PCM/VCM in VTD Fail Enable: The scan tool displays ACTIVE or INACTIVE. If applicable. The theft deterrent fuel enable is an input from the vehicle theft deterrent system that signals the PCM to enable the injectors and the crank relay if the proper signal is received. The scan tool will normally display INACTIVE. If the vehicle theft deterrent (VTD) system does not send the correct theft deterrent fuel enable signal to the PCM, the display will switch to ACTIVE and the fuel system and starter control may be disabled. Refer to vehicle theft deterrent diagnosis for further information.

PCM Reset: The scan tool displays Yes or No This parameter indicates when the internal PCM resets. The scan tool displays YES when an internal PCM reset occurred. The scan tool displays NO under the normal operating conditions.

Power Enrichment: The scan tool displays ACTIVE or INACTIVE. ACTIVE displayed indicates that the PCM has detected conditions appropriate to operate in Power Enrichment mode.

Short Term FT: The scan tool range is - -10 to +10 percent. Short term fuel trim represents a short term correction to fuel delivery by the PCM.

Spark: The scan tool range is -64 to 64 degrees. Displays the spark timing being commanded by the PCM on the IC circuit. A negative (-) value indicates degrees before top dead center (BTDC) or spark advance. A positive value indicates degrees after top dead center (ATDC) or spark retard.

Start-Up ECT: The scan tool range is -40 to +151°C (-40 to +304°F). Indicates the engine coolant temperature at the time that the vehicle was started.

Start-Up IAT: The scan tool range is -40 to +151°C (-40 to +304°F). Indicates the intake air temperature (IAT) at the time that the vehicle was started.

Starter Enable Relay Circuit Status: The scan tool displays Fault/OK This parameter indicates the state of the driver circuit for this device.

Starter Relay Command: The scan tool displays ON or OFF OFF indicates that the PCM is not allowing starter operation due to the engine running, excessive cranking time, trans not in P/N or other factors.

TCC Brake Pedal Switch: The scan tool displays RELEASED or APPLIED. This input to the PCM represents the state of the vehicle brake pedal. When the brake switch indicates that the brake pedal is APPLIED, the PCM will command the transaxle torque converter clutch (TCC) to disengage.

TCC PWM solenoid Command: The scan tool displays ON or OFF. Indicates the commanded state of the transaxle torque converter clutch (TCC).

TFP Sw.: The scan tool displays PARK/NEUTRAL, REVERSE, DRIVE 4, DRIVE 3, DRIVE 2, or LOW. This represents the decoded status of the four inputs from the transaxle range switch. The combination of transaxle inputs indicates the position of the transaxle manual valve.

Torque Delivered Signal: The scan tool range is 0-100 percent This parameter indicates the amount of available engine torque.

Torque Request Signal: The scan tool range is 0-100 percent This parameter indicates the desired amount of torque requested by the EBTCM.

TP Sensor: The scan tool range is 0-100 percent or 0.00-5.00 volts. The voltage being monitored by the PCM on the TP sensor signal circuit.

Traction Control Status: The scan tool displays Active or Inactive The scan tool displays active if the PCM receives a signal from the electronic brake and traction control module (EBTCM ) requesting torque reduction during a traction control event.

Vehicle Speed Sensor: The scan tool range is 0-255 km/h (0-155 mph). The vehicle speed sensor (VSS) signal is converted into km/h and mph for display.

VTD Auto Learn Timer: The scan tool displays ACTIVE or INACTIVE. The auto learn timer is the indication if the vehicle theft deterrent (VTD) system is in the learn mode and has not timed out.

VTD Fuel Disable : The scan tool displays ACTIVE or INACTIVE. If applicable. The theft deterrent fuel enable is an input from the vehicle theft deterrent system that signals the PCM to enable the injectors and the crank relay if the proper signal is received. The scan tool will normally display INACTIVE. If the vehicle theft deterrent system does not send the correct theft deterrent fuel enable signal to the PCM, the display will switch to ACTIVE and the fuel system and starter control may be disabled. Refer to vehicle theft deterrent diagnosis for further information.

VTD Fuel Disable Until Ign. OFF: The scan tool displays Yes or NO With the ignition ON and a VTD code present, the scan tool displays Yes.