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 negative number equals a longer shift time.

1-2 Shift Time: This parameter is the actual shift time of the last 1-2 shift. The shift time is based on a gear box ratio change after the commanded 1-2 shift.

1-2 Sol. (Solenoid): Displays On or Off. This parameter is the commanded state of the 1-2 shift solenoid valve. On indicates a commanded energized solenoid state, and Off indicates a commanded non-energized solenoid state.

1-2 Sol. (Solenoid) Open/Short to GND: Displays Yes or No. This parameter indicates whether an open or a short to ground exists in the 1-2 shift solenoid valve feedback signal to the PCM. The 1-2 shift solenoid valve must be commanded Off for this parameter to be valid.

1-2 Sol. (Solenoid) Short to Volts: Displays Yes or No. This parameter indicates whether a short to battery, B+, exists in the 1-2 shift solenoid valve feedback signal to the PCM. The 1-2 shift solenoid valve must be commanded On for this parameter to be valid.

1-2 TAP Cell (4-16): The amount of adapt pressure, based on 17 N·m (12.5 lb ft) of engine torque increment per cell, added to or subtracted from shift pressure during a 1-2 upshift. A large positive number means the PCM has seen several long shifts and has added PC solenoid pressure in order to decrease the shift time. A large negative number means the PCM has seen several short shifts and has removed PC solenoid pressure in order to increase the shift time.

2-3 Shift Error: This parameter is the difference between the desired 2-3 shift time and the actual 2-3 shift time. A negative number equals a longer shift time.

2-3 Shift Time: This parameter is the actual shift time of the last 2-3 shift. The shift time is based on a gear box ratio change after the commanded 2-3 shift.

2-3 Sol. (Solenoid): Displays On or Off. This parameter is the commanded state of the 2-3 shift solenoid valve. On indicates a commanded energized state, and Off indicates a commanded non-energized state.

2-3 Sol. (Solenoid) Open/Short to GND: Displays Yes or No. This parameter indicates whether an open or a short to ground exists in the 2-3 shift solenoid valve feedback signal to the PCM. The 2-3 shift solenoid valve must be commanded Off for this parameter to be valid.

2-3 Sol. (Solenoid) Short to Volts: Displays Yes or No. This parameter indicates whether a short to battery, B+, exists in the 2-3 shift solenoid valve feedback signal to the PCM. The 2-3 shift solenoid valve must be commanded On for this parameter to be valid.

2-3 TAP Cell (4-16): The amount of adapt pressure, based on 17 N·m (12.5 lb ft) of engine torque increment per cell, added to or subtracted from shift pressure during a 2-3 upshift. A large positive number means the PCM has seen several long shifts and has added PC solenoid pressure in order to decrease the shift time. A large negative number means the PCM has seen several short shifts and has removed PC solenoid pressure in order to increase the shift time.

3-4 Shift Error: This parameter is the difference between the desired 3-4 shift time and the actual 3-4 shift time. A negative number equals a longer shift time.

3-4 Shift Time: This parameter is the actual shift time of the last 3-4 shift. The shift time is based on a gear box ratio change after the commanded 3-4 shift.

3-4 TAP Cell (4-16): The amount of adapt pressure, based on 17 N·m (12.5 lb ft) of engine torque increment per cell, added to or subtracted from shift pressure during a 3-4 upshift. A large positive number means the PCM has seen several long shifts and has added PC solenoid pressure in order to decrease the shift time. A large negative number means the PCM has seen several short shifts and has removed PC solenoid pressure in order to increase the shift time.

A/C Clutch: Displays On or Off. This represents the PCM commanded state of the A/C compressor clutch relay driver circuit. The A/C compressor clutch should be engaged when On displays. When the display indicates On, the line pressure and the shift times will be adjusted for the additional engine load.

Commanded Gear: This parameter indicates the current commanded gear.

Cruise: Displays Enabled or Disabled. When the display indicates Enabled, the PCM is allowing cruise control operation. When the display indicates Disabled, the PCM has disabled cruise control operation. The PCM has the ability to disable cruise control under certain conditions. When the cruise control is On, shift patterns will be altered for 2-3 and 3-4 upshifts for 4-3 and 3-2 downshifts.

Current TAP (Transmission Adaptive Pressure) Cell: 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): The ECT sensor is mounted in the coolant stream and sends engine temperature information to the PCM. The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold, the internal resistance is high, the PCM monitors a high signal voltage. The PCM interprets this voltage as a cold engine. As the sensor warms, the internal resistance decreases, the voltage signal will decrease. The PCM interprets the lower voltage as a warm engine.

Engine Run Time: Displays hours/minutes/seconds. This parameter indicates the time elapsed since the engine was started. If the engine is stopped, this parameter is reset to 00:00:00.

Engine Speed: The engine speed is computed by the PCM from the fuel control reference input, the crankshaft position sensor. This parameter indicates the rotational speed of the engine expressed as revolutions per minute.

Engine Torque: This parameter is the torque delivered by the engine.

Gear Ratio: This parameter is the calculated gear ratio for all forward and reverse gears. The display reads 3.98 in all range selector positions when there is no vehicle speed.

Ignition Voltage: This parameter is the system voltage measured by the PCM at the PCM ignition input when the ignition switch is in the RUN position.

IMS (Internal Mode Switch): Displays Park, Park/Reverse, Reverse, Reverse/Neutral, Neutral, Neutral/Drive 4, Drive 4, Drive 4/Drive 3, Drive 3, Drive 3/Drive 2, Drive 2, Drive 2/Drive 1, Drive 1, Invalid or Open. The IMS Range display represents a decoded status of the four inputs from the IMS. This range includes all possible in-between gear states as well as the detent gear states. The combination of IMS inputs to the PCM are used by the PCM in order to determine what position the manual valve is in at any time.

IMS (Internal Mode Switch) A/B/C/P: Displays LOW or HI for the state of each of the four inputs from the IMS. LOW displayed indicates a low voltage signal, 0 volts, being monitored at the PCM. HI displayed indicates a high voltage signal, B+, being monitored at the PCM.

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

PC Sol. (Pressure Control Solenoid) Actual Current: This parameter is the actual current flow through the PC solenoid valve circuit, as measured by the PCM. Low current flow indicates high line pressure. High current flow indicates low line pressure.

PC Sol. (Pressure Control Solenoid) Duty Cycle: This parameter indicates the commanded state of the PC solenoid valve circuit, expressed as a percentage of ON time energized. A 0 percent duty cycle indicates no current flow zero ON time. High current flow is approximately 60 percent duty cycle at idle.

PC Sol. Ref. (Pressure Control Solenoid Reference) Current: This parameter is the current flow commanded by the PCM through the PC solenoid valve circuit. Low current flow indicates high line pressure. High current flow indicates low line pressure.

Steady State TAP 1GR: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the first gear ratio, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP 2GR: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the second gear ratio, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP 2GR/TCC: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the second gear ratio with TCC applied, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP 3GR: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the third gear ratio, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP 3GR/TCC: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the third gear ratio with TCC applied, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP 4GR: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the fourth gear ratio, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP 4GR/TCC: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the fourth gear ratio with TCC applied, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

Steady State TAP Reverse: The amount of adapt pressure that is applied to PC solenoid pressure to maintain the reverse gear ratio, eliminate clutch or band slip. A large number means the PCM has seen an element slipping and is compensating with adapt pressure.

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 (Torque Converter Clutch) Duty Cycle: This display indicates the commanded percent of the TCC PWM solenoid valve On time. A value of 20 percent represents an energized commanded state and a value of 0 percent represents a de-energized commanded state. The commanded state is applied at vehicle speeds that are above approximately 16 km/h (10 mph).

TCC (Torque Converter Clutch) 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. The TCC PWM solenoid valve must be commanded Off for this parameter to be valid. The Scan tool will display Yes only while the TCC PWM solenoid valve is Off. The display will pulsate.

TCC (Torque Converter Clutch) Duty Cycle Short to Volts: Displays Yes or No. This parameter indicates whether a short to battery, B+, exists in the TCC PWM solenoid valve feedback signal to the PCM. The TCC PWM solenoid valve must be commanded On for this parameter to be valid. The scan tool will display Yes only while the TCC PWM solenoid valve is On. The display will pulsate.

TCC (Torque Converter Clutch) Release Pressure: Displays Yes or No. This parameter is the status of the normally-closed TCC release switch. A scan tool displaying Yes indicates the switch is open, TCC release fluid pressure is present and the TCC is released. A scan tool displaying No indicates the switch is closed, TCC release fluid pressure is not present and the TCC is applied.

TCC (Torque Converter Clutch) Slip Speed: This display is the difference between the transmission input shaft RPM and the engine RPM. A negative value indicates deceleration. A value of near zero indicates that the TCC is applied.

TFP Sw (Transmission Fluid Pressure Switch): Displays Park, Reverse, Neutral, Drive 4, Drive 3, Drive 2, Drive 1 or Invalid. TFP Sw display represents a decoded status of the three inputs A/B/C to the PCM from the TFP manual valve position switch.

TFP Sw (Transmission Fluid Pressure Switch) A/B/C: Displays HI/LOW, HI/LOW, HI/LOW. This parameter indicates the status of each of the three inputs from the transmission fluid pressure switch to the PCM. HI indicates an ignition voltage input to the PCM. LOW indicates a zero voltage input to the PCM.

TFT (Transmission Fluid Temperature) Sensor: This display shows the voltage drop across the TFT sensor. The PCM applies 5 volts to the TFT sensor circuit. The sensor is a thermistor which changes internal resistance as the temperature changes. When the sensor is cold, the internal resistance is high, the PCM monitors a high signal voltage. The PCM interprets this voltage as a cold transmission. As the sensor warms, the internal resistance decreases, the voltage signal will decrease. The PCM interprets the lower voltage as a warm transmission.

TP (Throttle Position) Angle: The TP angle is computed by the PCM from the TP sensor voltage. The TP angle should display 0 percent at idle and 100 percent at wide open throttle (WOT).

TP (Throttle Position) Sensor: This parameter indicates the voltage being monitored by the PCM on the TP sensor signal circuit.

TR Sw. (Transmission Range Switch): Displays Park/Neutral, Reverse, Drive 4, Drive 3, Drive 2, Drive 1 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.

TR Sw. (Transmission Range Switch) A/B/C/P: Displays HI or LOW for the status of the four inputs from the transmission range switch to the PCM. HI indicates an ignition voltage input to the PCM. LOW indicates a zero voltage input to the PCM.

Traction Control: Displays Active or Inactive. The scan tool displays Active when the PCM receives a request for torque reduction from the electronic brake traction control module (EBTCM).

Trans. Fluid Temp. (Transmission Fluid Temperature): This display is the temperature conversion of the voltage input signal to the PCM of the TFT. When the TFT is high, 151°C (304°F), the signal voltage is low, 0 volts. When the TFT is low, -40°C (-40°F), the signal voltage is high, 5 volts.

Transmission Hot Mode: Displays On or Off. This display indicates the automatic transmission fluid temperature (TFT). Off indicates that the TFT has not exceeded 130°C (266°F). On indicates that the TFT has exceeded 130°C (266°F) and has not cooled to 120°C (248°F) for more that 5 seconds. Note: these numbers are approximate. They differ with transmissions.

Transmission ISS (Input Shaft Speed): This parameter is the rotational speed of the transmission input shaft.

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

Vehicle Speed: This parameter is the vehicle speed sensor (VSS) input signal converted by the PCM to be displayed as vehicle speed in both metric and English units.