GM Service Manual Online
For 1990-2009 cars only
BARO: Displays a range of 10-104 kPa, 0.00-5.00V. The BARO Sensor measures barometric pressure during the ignition ON cycle and during Wide Open Throttle (WOT). This allows the PCM/VCM to make fuel delivery, spark timing, and transmission line pressure adjustments for changing altitudes.

MAP (Manifold Absolute Pressure): Displays a range of 10-104 kPa, 0.00-5.00V. The MAP sensor, which is attached to the intake manifold, measures changes in intake manifold pressure. These changes result from engine speed and load changes. The PCM/VCM uses this information to adjust fuel delivery and spark plug timing according to incoming air density.

TP (Throttle Position) Sensor: Displays a range of 0.00-5.00V. The TP sensor is used by the PCM/VCM to determine the amount of throttle demanded by the driver. Voltage is below 1 volt at idle and above 4 volts at Wide Open Throttle (WOT).

TP (Throttle Position) Angle: Displays a range of 0-100%. The TP angle is computed by the PCM/VCM from the TP sensor voltage. The TP angle should read 0% at idle and 100% at Wide Open Throttle (WOT).

A/C Clutch: Displays ON or OFF. This parameter indicates the commanded state of the A/C control relay. The clutch should be engaged when ON displays.

Cruise Enabled: Displays ON or OFF. This parameter indicates whether the PCM/VCM is allowing cruise operation. The PCM/VCM has the ability to disable cruise control under certain conditions.

Hot Mode: Displays Yes or No. This parameter monitors transmission temperature. No indicates that the transmission temperature has not exceeded 127°C (261°F). Yes indicates that the transmission temperature has exceeded 135°C (275°F).

Adaptable Shift: Displays Yes or No. Yes indicates that the proper operating conditions were all within the proper operating range during the last shift, and that the Shift Time was accurate. This shift information is then used through the adaptive function in order to update the adapt cells. No indicates that not all of the operating conditions were met in order to enable this function, and that the adapt cells were not updated. Proper operating conditions include TP Sensor Delta, Engine Torque, Vehicle Speed Delta, Engine Vacuum, and Shift Delay.

Current TAP (Transmission Adaptive Pressure) Memory: Displays a range of -16 to +16 psi. This parameter is the amount of pressure that is added to base line pressure to adjust the holding effort of a clutch or a band, while shifting.

Current TAP (Transmission Adaptive Pressure): Displays a TP cell range of 0-16. This parameter indicates the current throttle position cell used for line pressure modification (adaptation).

Long Shift Delay: Displays Yes or No. This parameter indicates whether a long shift delay occurred during the last shift. YES indicates that a long shift delay occurred. NO indicates that a long shift delay did not occur. A shift delay is determined from the time that the PCM/VCM commands the shift until the start of the engine RPM drop. When a shift delay is within a range that enables shift adapts, NO is indicated.

Long Shift Time: Displays Yes or No. This parameter indicates whether a long shift time occurred during the last shift. YES indicates that a long shift time occurred. NO indicates that a long shift time did not occur. Shift time is calculated from the beginning of the engine RPM drop to the beginning of the engine RPM increase. When shift time is within a range that enables shift adapts, NO is indicated.

TP Range: Displays Normal (Yes) or Exceeded (No). This parameter indicates when the throttle position is within a range that enables shift adapts. Normal (Yes) indicates that the TP is within the range. Exceeded (No) indicates that the TP is not within the range.

Standard TAP (Transmission Adaptive Pressure): Displays Yes or No. The standard TAP is an amount of pressure that is added to the base line pressure. If the shift requires standard TAP to achieve the shift, then the scan tool displays Yes. If the shift requires more or less than the standard TAP to achieve the shift, then the scan tool displays No, indicating that the TAP is out of the standard range.

VSS Delta: Displays Normal (Yes) or Exceeded (No). This parameter indicates when the VSS is within a range that enables shift adapts. Normal (Yes) indicates that the VSS is within the range. Exceeded (No) indicates that the VSS is not within the range.

TP Delta: Displays Normal or Exceeded. This parameter indicates when the TP is within a TP delta range that enables shift adapts. A TP delta range is how much the TP is moved during the shift calculation. Normal indicates that the TP is within the range. Exceeded indicates that the TP is not within the range.

Engine Run Time: Displays a range of 0:00:00-18:12:15 hr/min/sec. This parameter measures how long the engine has been operating. When the ignition switch is turned OFF, the value is reset to zero.

History Malfunctions: Displays a number. This parameter displays the number of DTCs stored in memory.

Active Malfunctions: Displays a number. This parameter displays the number of active DTCs.

Ignition Volts: Displays a range of 0.0-25.5V. This represents the system voltage measured by the PCM/VCM at its ignition feed.

Gear Ratio: Displays a range of 0.00-3.98-1. This parameter is the actual gear ratio of the current commanded gear. The parameter is not a calculated gear ratio.

Current Gear: Displays 1, 2, 3, or 4. This parameter indicates the current commanded state of the shift solenoids.

TFT (Automatic Transmission Fluid Temperature): Displays a range of -40°C to 151°C (-40°F to 304°F). This parameter is the input signal of the transmission fluid temperature sensor. Transmission fluid temperature is high (151°C) when signal voltage is low (0V), and transmission fluid temperature is low (-40°) when signal voltage is high (5V).

ECT (Engine Coolant Temperature): Displays a range of -40°C to 151°C (-40°F to 304°F). This parameter is the input signal of the engine coolant temperature sensor. The engine coolant temperature is high (151°C) when the signal voltage is low (0V), and the engine coolant temperature is low (-40°) when the signal voltage is high (5V).

TFT (Transmission Fluid Temperature) Sensor: Displays a range of 0.00-5.00V. When the transmission fluid is cold, the sensor resistance is high and the VCM will sense high signal voltage. As the transmission fluid temperature warms to normal operating temperature, the sensor resistance becomes less and the voltage decreases to about 1.5-2.0V.

TCC (Torque Converter Clutch) Slip Speed: Displays a range of -4080 to 4079 RPM. This parameter is the difference between transmission output speed and engine speed. A negative value indicates that the engine speed is less than the output speed (deceleration). A positive value indicates that the engine speed is greater than the output speed (acceleration). A value of zero indicates that the engine speed is equal to the output speed (TCC applied).

Brake Switch: Displays Open or Closed. This parameter indicates the state of the brake switch circuit input. Open indicates a zero voltage input (brake switch open, brake pedal applied). Closed indicates a B+ voltage input (brake switch closed, brake pedal released).

TCC Duty Cycle: Displays a range of 0-100%. This parameter is the commanded percentage of ON time of the TCC PWM solenoid. 90% represents an ON (energized) commanded state. 0% represents an OFF (non-energized) commanded state. This commanded state is applied at a vehicle speed between approximately 0-16 km/h (0-10 mph).

TCC Enable: Displays ON or OFF. This parameter is the commanded state of the TCC solenoid. ON indicates a commanded energized state (current is flowing through the solenoid). OFF indicates a commanded non-energized state (current is not flowing through the solenoid). This commanded state occurs at various vehicle speeds between applications.

TCC Duty Open: Displays Yes or No. This parameter indicates whether an open or a short to ground exists in the TCC PWM solenoid valve feedback signal to the VCM.

TCC Duty Shorted: Displays Yes or No. This parameter indicates whether a short to B+ exists in the TCC PWM solenoid valve feedback signal to the VCM.

TCC Enable Open: Displays Yes or No. This parameter indicates whether an open or a short to ground exists in the TCC solenoid valve feedback signal to the VCM.

TCC Enable Short: Displays Yes or No. This parameter indicates whether a short to B+ exists in the TCC solenoid valve feedback signal to the VCM.

1-2 Sol / 2-3 Sol: Displays ON or OFF. These parameters are the commanded status of the 1-2 and the 2-3 shift solenoid valves. ON represents a commanded energized state (current is flowing through the solenoid). OFF represents a non-commanded state (current is not flowing through the solenoid).

1-2 Sol. Open: Displays Yes or No. This parameter indicates if an open or short to ground exists in the 1-2 shift solenoid valve feedback signal to the VCM.

1-2 Sol. Short: Displays Yes or No. This parameter indicates if a short to B+ exists in the 1-2 shift solenoid valve feedback signal to the VCM.

2-3 Sol. Open: Displays Yes or No. This parameter indicates if an open or short to ground exists in the 2-3 shift solenoid valve feedback signal to the VCM.

2-3 Sol. Short: Displays Yes or No. This parameter indicates if a short to B+ exists in the 2-3 shift solenoid valve feedback signal to the VCM.

3-2 Downshift: Displays Yes or No. This parameter indicates if the 3-2 shift solenoid valve assembly is currently commanded On or Off. Yes indicates that the 3-2 shift solenoid valve assembly is ON. No indicates that the 3-2 shift solenoid valve assembly is OFF. The solenoid commanded state is based on the transmission temperature. The solenoid will change states during a 3-2 downshift to regulate the appropriate pressure. The commanded state of the solenoid occurs at approximately 30 mph with a throttle increase.

1-2 Shift Time: Displays a range of 0.00-6.38 seconds. This parameter is the actual time of the last 1-2 shift. The shift time is based on the engine RPM drop after the commanded 1-2 shift. This value is only accurate if the Adaptable Shift parameter indicates Yes.

2-3 Shift Time: Displays a range of 0.00-6.38 seconds. This parameter is the actual time of the last 2-3 shift. The shift time is based on the engine RPM drop after the commanded 2-3 shift. This value is only accurate if the Adaptable Shift parameter indicates Yes.

1-2 Shift Error: Displays a range of -6.38 to +6.38 seconds. This parameter is the difference between the desired 1-2 shift time and the actual 1-2 shift time. This value is only accurate if the Adaptable Shift parameter indicates Yes.

2-3 Shift Error: Displays a range of -6.38 to +6.38 seconds. This parameter is the difference between the desired 2-3 shift time and the actual 1-2 shift time. This value is only accurate if the Adaptable Shift parameter indicates Yes.

3-4 Shift Time: Displays a range of 0.00-6.38 seconds. This parameter is the actual time of the last 3-4 shift. The shift time is based on the engine RPM drop after the commanded 3-4 shift. This value is only accurate if the Adaptable Shift parameter indicates Yes.

3-4 Shift Error:  Displays a range of -6.38 to +6.38 seconds. This parameter is the difference between the desired 3-4 shift time and the actual 3-4 shift time. This value is only accurate if the adaptable shift parameter indicates Yes.

Latest Shift: Displays a range of 0.00-6.38 seconds. This parameter is the actual shift time of the last upshift. This value is only accurate if the Adaptable Shift parameter indicates Yes.

Latest Shift Error: Displays a range of -6.38 to +6.38 seconds. This parameter is the difference between the latest desired shift time and the latest actual shift time. This value is only accurate if the Adaptable Shift parameter indicates Yes.

Shift Delay: Displays a range of 0.00-6.38. seconds. This parameter indicates the time between the PCM/VCM command to the shift, and the start of the drop in engine RPM.

Speed Ratio: Displays a range of 0.00:1-8.00:1. This parameter indicates engine speed divided by transmission output speed. This value is used to estimate transmission gear ratio.

Upshift Request: Displays Yes or No. This parameter indicates when the PCM is requesting an upshift. Yes indicates an upshift is requested. No indicates an upshift is not requested.

Upshift In Progress: Displays Yes or No. This parameter indicates if the transmission is currently in an upshift. Yes indicates an upshift is in progress. No indicates an upshift is not in progress.

Upshift Desired: Displays Yes or No. This parameter indicates when the PCM desires an upshift. Yes indicates an upshift is desired. No indicates an upshift is not desired.

DS Requested: Displays Yes or No. This parameter indicates when the PCM is requesting a downshift. Yes indicates a downshift is requested. No indicates a downshift is not requested.

DS In Progress: Displays Yes or No. This parameter indicates if the transmission is currently in a downshift. Yes indicates a downshift is in progress. No indicates a downshift is not in progress.

DS Desired: Displays Yes or No. This parameter indicates when the PCM desires a downshift. Yes indicates a downshift is desired. No indicates a downshift is not desired.

Vehicle Speed: Displays a range of 0-255 km/h (0-158 mph). This parameter is the input signal from the vehicle speed sensor assembly.

Engine Speed: Displays a range of 0-8192 RPM. This parameter indicates the rotational speed of the engine expressed as revolutions per minute.

PC Act. (Actual) Current: Displays a range of 0.00-1.10 amps. This parameter is the actual current of the pressure control solenoid circuit at the control module. Zero amp (no current flow) indicates actual higher line pressure. Actual lower line pressure is indicated by 1.1 amps (high current flow).

PC Ref. (Reference) Current: Displays a range of 0.00-1.10 amps. This parameter is the commanded current of the pressure control solenoid circuit. Zero amp (no current flow) indicates commanded higher line pressure. Commanded lower line pressure is indicated by 1.1 amps (high current flow).

PC Duty Cycle: Displays a range of 0-100%. This parameter is the commanded state of the pressure control solenoid expressed as a percent of energized ON time. 0% indicates zero ON time (non-energized) or no current flow. Approximately 60% at idle indicates maximum ON time (energized) or high current flow.

Power Enrichment: Displays Active (Yes) or Inactive (No). This parameter indicates when the power enrichment mode is active (moderate to heavy acceleration). Active (Yes) indicates that the power enrichment mode is active. Inactive (No) indicates that the power enrichment mode is not active.

Kickdown Enabled: Displays Yes or No. This parameter indicates whether enabling conditions exist for an acceleration mode downshift. No indicates that enabling conditions such as throttle position, vehicle speed, or input speed do not exist for an acceleration mode downshift. Yes indicates that enabling conditions exist for an acceleration mode downshift.

DTC Set This Ign: Displays Yes or No. This parameter displays Yes if a DTC is active during the current ignition cycle.

TR Switch: Displays a range of Error, Reverse, Overdrive, Drive3, Drive2, Low, or Park/Neutral. These parameters are the decoded status of the three A/B/C range inputs from the Automatic Transmission Fluid Pressure Manual Valve Position Switch Assembly. These parameters represent the position of the transmission manual valve.

Trans OSS (Output Speed Sensor): Displays a range of 0-8192 RPM. This parameter indicates the rotational speed of the transmission output shaft expressed as revolutions per minute.

TFP Switch A/B/C: Displays On/Off, On/Off, On/Off. These parameters are the three inputs from the Automatic Transmission Fluid Pressure Manual Valve Position Switch Assembly. On represents a 0 voltage signal. Off represents a B+ voltage signal.

Loop Status: Displays Open or Closed. Closed indicates that the PCM is controlling fuel delivery according to the oxygen sensor voltage. Open indicates that the PCM ignores the oxygen sensor voltage and bases fuel delivery on inputs from the TP sensor, the ECT sensor, and the MAP sensor.

Desired Idle: Displays 0-3187 RPM. This parameter indicates the idle speed that is commanded by the VCM. The VCM will compensate for various engine loads based on the engine coolant temperature in order to keep the engine at the desired speed.

ECT Sensor: Displays 0.00-4.98V. When the sensor is cold (internal resistance is high), the VCM monitors a high signal voltage which the VCM interprets as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal decreases and the VCM interprets the lower voltage as a warm engine.

TCC Out of Range: Displays Yes or No. This parameter indicates whether or not the transmission is in a range which allows the TCC to apply. Yes indicates that the transmission is not in a range which allow the TCC to apply. No indicates that the transmission is in a valid range.

TCC Min. TP: Displays Yes or No. This parameter indicates whether or not the TP has achieved the minimum value needed in order to allow the TCC to apply. Yes indicates that the minimum TP value has not been achieved. No indicates that the minimum TP value has been achieved.

TCC Delta TP: Displays Yes or No. This parameter indicates when the TP value is within a TP Delta range that allows the TCC to apply. A TP Delta range is the amount that the TP moves during the shift calculation. A parameter of Yes indicates that the TP value changed too quickly. This will prevent the TCC from applying. No indicates that the TP value is within the range needed for the TCC to apply.

PC Sol Low: Displays Normal or Low Volts. This parameter indicates system voltage conditions to the VCM. This parameter is based on transmission temperature. A parameter of Normal indicates that the voltage to the VCM is within a range that allows the PC Sol Valve to function properly. Low Volts indicates that the voltage to the VCM is low, and the PC Sol Valve has turned off.

4WD Low: Displays Yes or No. This parameter is the signal state of the four-wheel drive low circuit. Yes indicates a 0 voltage signal (4WD Low requested). No indicates a B+ voltage signal (4WD Low not requested). If 4WD low is requested, the transmission output speed increases by a factor of the transfer case ratio.

Max TAP (Transmission Adaptive Pressure): Displays Yes or No. This parameter indicates when line pressure modification (adaptation) has reached its limit. Yes indicates that the limit has been reached. No indicates that the limit has not been reached.

Start of Shift: Displays Yes or No. This parameter indicates when an upshift has been detected. Yes is displayed briefly when an upshift has been detected. No indicates that an upshift has not been detected.

End of Shift: Displays Yes or No. This parameter indicates when an upshift has been completed. Yes is displayed briefly when an upshift has been completed. No indicates that an upshift has not just been completed.

Shift Completed: Displays Yes or No. This parameter indicates when a shift has been completed. Yes indicates that a shift has been completed, and this parameter will be displayed until the next shift occurs. No indicates that a shift has not been completed, and this parameter will be displayed during a shift.