GM Service Manual Online
For 1990-2009 cars only
1-2 Shift Error: This parameter is the difference between the desired 1-2 shift time and the actual 1-2 shift time. A positive number indicates a firm or fast shift, the actual shift time was shorter than the desired shift time. A negative number indicates a soft or slow shift, the actual shift time was longer than the desired shift time. This value is only accurate if the shift was adaptable.

1-2 Shift Time: 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 shift was adaptable.

1-2 Sol: Displays On or Off. This parameter is the commanded status of the 1-2 shift solenoid valve. 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/Short to GND: 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 PCM. This parameter is valid only when the 1-2 shift solenoid is commanded Off.

1-2 Sol. Short to Volts: Displays Yes or No. This parameter indicates if a short to voltage exists in the 1-2 shift solenoid valve feedback signal to the PCM. This parameter is valid only when the 1-2 shift solenoid is commanded On.

1-2 TAP Cell (4-16): Displays kPa or psi. This parameter displays the amount of pressure varied from a calibrated base line pressure for shifts. Each TAP Cell is based on a calibrated shift torque value. Each TAP Cell value is calculated from the last shift time. This cell pressure is used in addition to calibrated base line pressure to adjust the apply of a clutch or band during the next shift.

2-3 Shift Error: This parameter is the difference between the desired 2-3 shift time and the actual 2-3 shift time. A positive number indicates a firm or fast shift, the actual shift time was shorter than the desired shift time. A negative number indicates a soft or slow shift, the actual shift time was longer than the desired shift time. This value is only accurate if the shift was adaptable.

2-3 Shift Time: 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 shift was adaptable.

2-3 Sol: Displays On or Off. This parameter is the commanded status of the 2-3 shift solenoid valve. 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.

2-3 Sol. Open/Short to GND: 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 PCM. This parameter is valid only when the 2-3 shift solenoid is commanded Off.

2-3 Sol. Short to Volts: Displays Yes or No. This parameter indicates if a short to voltage exists in the 2-3 shift solenoid valve feedback signal to the PCM. This parameter is valid only when the 2-3 shift solenoid is commanded On.

2-3 TAP Cell (4-16): See 1-2 TAP Cell (4-16).

3-2 Downshift Sol.: Displays On or Off. This parameter indicates if the 3-2 shift solenoid valve assembly is currently commanded On or 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.

3-2 Sol. Open/Short to GND: Displays Yes or No. This parameter indicates when an open or a short to ground exists in the 3-2 shift solenoid valve assembly feedback signal to the PCM. This parameter is valid only when the 3-2 shift solenoid is commanded Off.

3-2 Sol. Short to Volts: Displays Yes or No. This parameter indicates whether a short to voltage exists in the 3-2 shift solenoid valve assembly feedback signal to the PCM. This parameter is valid only when the 3-2 shift solenoid is commanded On.

3-4 Shift Error: This parameter is the difference between the desired 3-4 shift time and the actual 3-4 shift time. A positive number indicates a firm or fast shift, the actual shift time was shorter than the desired shift time. A negative number indicates a soft or slow shift, the actual shift time was longer than the desired shift time. This value is only accurate if the shift was adaptable.

3-4 Shift Time: 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 shift was adaptable.

4WD: Displays Enabled or Disabled. This parameter indicates whether the vehicle is currently in a four-wheel drive mode.

4WD Low: Displays Enabled or Disabled. This parameter is the signal state of the four-wheel drive low circuit. Enabled indicates a 0 voltage signal, 4WD Low requested. Disabled indicates a B+ voltage signal, 4WD Low not requested.

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.

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

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

Current TAP (Transmission Adaptive Pressure) Cell: The scan tool displays cells 4-16. This parameter indicates the current TAP cell in use for transmission line pressure adaptation. The cells are based on engine torque. The higher the engine torque, the higher the current TAP cell. The last cell used will remain displayed until the next adaptable upshift occurs.

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

Engine Run Time: This parameter measures how long the engine has been operating. When the ignition switch is turned OFF, the value is reset to zero.

Engine Speed: This parameter indicates the rotational speed of the engine expressed as revolutions per minute.

Engine Torque: This parameter indicates the amount of torque that is delivered from the engine.

Estimated Gear Ratio: This parameter indicates the estimated turbine speed divided by the transmission output speed. Estimated turbine speed is calculated from engine speed and engine torque.

Ignition Voltage: This represents the system voltage measured by the PCM at its ignition feed.

Last Shift Time: This parameter is the actual shift time of the last shift.

P1870 Slip Counter: Displays 0, 1 or 2. This parameter is the number of times the P1870 diagnostic test has identified a slipping condition. This diagnostic test is required to identify a slipping condition three times in a row in order to set the DTC P1870 Transmission Component Slipping Diagnostic code.

PC Sol. Actual Current: 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 Solenoid Duty Cycle: This parameter is the commanded state of the pressure control solenoid expressed as a percent of energized ON time. A reading of 0% indicates zero ON time, non-energized, or no current flow. Approximately 60% at idle indicates maximum ON time, energized, or high current flow.

PC Sol. Ref. (Reference) Current: 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.

Power Take-Off: Displays Yes or No. This parameter indicates when the Power Take Off (PTO) is engaged. PTO mode disables all transmission diagnostics.

Speed Ratio: This parameter indicates engine speed divided by transmission output speed. This value is used to estimate transmission gear ratio.

TCC (Torque Converter Clutch) 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: This parameter is the commanded percentage of ON time of the TCC PWM solenoid. Approximately 90% represents an ON, energized, commanded state. A reading of 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 Duty Cycle Open/Short to GND: 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 PCM. This parameter is valid only when the TCC PWM solenoid is commanded OFF, duty cycle is 0%.

TCC Duty Cycle Short to Volts: Displays Yes or No. This parameter indicates whether a short to voltage exists in the TCC PWM solenoid valve feedback signal to the PCM. This parameter is valid only when the TCC PWM solenoid is commanded ON, duty cycle is at maximum.

TCC Enable: Displays Yes or No. This parameter is the commanded state of the TCC solenoid. Yes indicates a commanded energized state, current is flowing through the solenoid. No indicates a commanded non-energized state, current is not flowing through the solenoid. This commanded state occurs at various vehicle speeds between applications.

TCC Enable Open/Short to GND: 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 PCM. This parameter is valid only when the TCC solenoid is commanded OFF.

TCC Enable Short to Volts: Displays Yes or No. This parameter indicates whether a short to voltage exists in the TCC solenoid valve feedback signal to the PCM. This parameter is valid only when the TCC solenoid is commanded ON.

TCC Slip Speed: 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.

TFP Sw.: Displays Park/Neutral, Reverse, Drive4, Drive3, Drive2, Drive1 or Invalid. This parameter is the decoded status of the three A/B/C inputs from the automatic transmission fluid pressure manual valve position switch. Invalid is displayed when the PCM does not recognize a valid combination of inputs.

TFP Sw. A/B/C: Displays HI/LOW, HI/LOW, HI/LOW. This parameter indicates the status of the three inputs from the Automatic Transmission Fluid Pressure Manual Valve Position Switch Assembly to the PCM. LOW represents a zero voltage signal. HI represents an ignition voltage signal.

TFT (Transmission Fluid Temperature) Sensor: When the transmission fluid is cold, the sensor resistance is high and the PCM will sense high signal voltage. As the transmission fluid temperature warms to a normal operating temperature, the sensor resistance becomes less and the voltage decreases.

Torque Converter Efficiency - (Ratio): The ratio is calculated by multiplying the speed ratio by a value related to the "K factor" of the torque converter. The "K factor" is the looseness or tightness of the torque converter for a given torque. The nearer the torque converter is to full coupling, i.e. 1:1, the closer the torque converter efficiency number will be to 1.

Tow/Haul Mode: Displays Active or Inactive. This parameter indicates when the transmission is operating in a towing or hauling mode. In tow/haul mode, the PCM commands a different shift pattern that increases performance when towing or hauling. Shift quality and TCC scheduling are also affected during tow/haul mode operation.

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

TP (Throttle Position) Sensor: The TP sensor is used by the PCM 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).

TR Sw.: Displays Park/Neutral, Reverse, Drive4, Drive3, Drive2, Drive1 or Invalid. This parameter is the decoded status of the four A/B/C/P inputs from the transmission range switch. Invalid is displayed when the PCM does not recognize a valid combination of inputs.

Traction Control: Displays Active or Inactive. When the PCM receives a request for torque reduction from the electronic brake traction control module (EBTCM) Active is displayed.

Transfer Case Ratio: This parameter indicates the ratio of the transfer case calculated from engine speed divided by transmission output speed based on the commanded gear.

Trans. Fluid Temp.: This parameter is the input signal of the transmission fluid temperature sensor. Transmission fluid temperature is high (151°C/304°F) when signal voltage is low, 0 V, and transmission fluid temperature is low (-40°C/-40°F) when signal voltage is high, 5 V.

Transmission Hot Mode: Displays ON or OFF. This parameter monitors transmission temperature. ON indicates that the transmission temperature has exceeded 135°C (275°F).

Transmission OSS (Output Shaft Speed): This parameter indicates the rotational speed of the transmission output shaft expressed as revolutions per minute.

Vehicle Speed: This parameter is the input signal from the vehicle speed sensor assembly.