For 1990-2009 cars

Table 1: | Scan Tool Data Parameters
Table 2: | Scan Tool Output Controls

The Transmission Control Module Scan Tool Data List contains all transmission related parameters that are available on the scan tool. The list is arranged in alphabetical order. A given parameter may appear in any one of the data lists, and in some cases may appear more than once, or in more than one data list in order to group certain related parameters together.

The values below represent a typical display recorded from a properly functioning system.

Important: Do not use a scan tool that displays faulty data. Report the condition to the scan tool manufacturer. The use of a faulty scan tool can result in misdiagnosis and the unnecessary replacement of parts.

Only the parameters listed below are used/referenced in this manual for diagnosis. If a scan tool displays other parameters, those values are not recommended by General Motors for use in diagnosis.

If all values are within the expected range described below, refer to Symptoms - Automatic Transmission for diagnosis.

The scan tool values from a properly functioning transmission may be used for comparison with the transmission you are diagnosing. The values below represent a typical display recorded from a properly functioning system.

#### Scan Tool Data Parameters

Parameter | System State | Expected Value | Description
--- | --- | --- | ---
Operating Conditions: Engine at idle, upper radiator hose hot, closed throttle, transmission in Park, closed loop operation, accessories OFF, brake pedal not applied.
1-2 Shift Error | -- | Seconds, Varies | This parameter displays 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 | -- | Seconds, Varies | This parameter displays 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. | -- | On | This parameter displays the commanded state of the 1-2 shift solenoid valve. When the transmission is in FIRST and FOURTH gear, the display should indicate ON, current is flowing through the solenoid. When the transmission is in SECOND and THIRD gear, the display should indicate OFF, current is not flowing through the solenoid.
1-2 Sol. CKT Status | -- | OK | This parameter displays the solenoid valve feedback voltage signal circuit status on the scan tool. If the voltage is low when the solenoid is commanded OFF, the scan tool will display Open/Short to GND. If the voltage is high when the solenoid is commanded ON, the scan tool will display Short to Volts. If no circuit fault is present the scan tool will display OK.
1-2 TAP Cell (4-14) | -- | kPa (psi), Varies | This parameter displays the amount of transmission adaptive pressure (TAP), 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 positive number indicates that long shifts have been detected and PC solenoid pressure has been added in order to decrease shift time. A negative number indicates that short shifts have been detected and PC solenoid pressure has been subtracted in order to increase shift time.
2-3 Shift Error | -- | Seconds, Varies | This parameter displays 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 | -- | Seconds, Varies | This parameter displays 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 Sol. | -- | On | This parameter displays the commanded state of the 2-3 shift solenoid valve. When the transmission is in FIRST and SECOND gear the display should indicate ON, current is not flowing through the solenoid. When the transmission is in THIRD and FOURTH gear, the display should indicate OFF, current is flowing through the solenoid.
2-3 Sol. CKT Status | -- | OK | This parameter displays the solenoid valve feedback voltage signal circuit status on the scan tool. If the voltage is low when the solenoid is commanded OFF, the scan tool will display Open/Short to GND. If the voltage is high when the solenoid is commanded ON, the scan tool will display Short to Volts. If no circuit fault is present the scan tool will display OK.
2-3 TAP Cell (4-14) | -- | kPa (psi), Varies | This parameter displays the amount of transmission adaptive pressure (TAP), 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 positive number indicates that long shifts have been detected and PC solenoid pressure has been added in order to decrease shift time. A negative number indicates that short shifts have been detected and PC solenoid pressure has been subtracted in order to increase shift time.
3-2 Downshift Sol. | -- | On | This parameter displays 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 48 km/h (30 mph) with a throttle increase. The scan tool displays On or Off.
3-2 Sol. CKT Status | -- | OK | This parameter displays the solenoid valve feedback voltage signal circuit status on the scan tool. If the voltage is low when the solenoid is commanded OFF, the scan tool will display Open/Short to GND. If the voltage is high when the solenoid is commanded ON, the scan tool will display Short to Volts. If no circuit fault is present the scan tool will display OK.
3-4 Shift Error | -- | Seconds, Varies | This parameter displays 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 | -- | Seconds, Varies | This parameter displays 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 | -- | Disabled | This parameter displays whether the vehicle is currently in a four-wheel drive mode. Displays Enabled or Disabled
4WD Low | -- | Disabled | This parameter displays the signal state of the four-wheel drive low circuit. Enabled indicates a 0 voltage signal requesting 4WD low. Disabled indicates a B+ voltage signal which does not request 4WD low. The scan tool displays Enabled or Disabled.
A/C Clutch | -- | Off | This parameter displays the commanded state of the air conditioning (A/C) compressor clutch relay driver circuit and displays On or Off. 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 | -- | 1 | This parameter displays the current commanded state of the shift solenoid valves. The scan tool displays 1,2,3,4 or 5.
Cruise | -- | Disabled | This parameter displays the commanded state of the cruise control system. The scan tool 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. When the cruise control display is ENABLED, shift patterns will be altered for 2-3 and 3-4 upshifts or 4-3 and 3-2 downshifts.
Current TAP Cell | -- | kPa, (psi), Varies | This parameter displays the current transmission adaptive pressure (TAP) cell in use for transmission line pressure adaptation. The cells are based on 17 N·m (12.5 lb ft) of 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 | -- | °C (°F), Varies | This parameter displays the input signal from the engine coolant temperature (ECT) sensor. ECT is high at 151°C (304°F) when the signal voltage is low 0 volt. ECT is low at -40°C (-40°F) when the signal voltage is high 5 volt.
Engine Run Time | -- | Hr/Min/Sec, Varies | This parameter displays a measure in Hr:Min:Sec of the length of time the engine has been operating. When the ignition is cycled to OFF, the value is reset to zero.
Engine Speed | -- | RPM, Varies | This parameter displays the rotational speed of the engine expressed as revolutions per minute.
Engine Torque | -- | N·m, Varies | This parameter displays a calculated value based on engine load, throttle position, mass air flow, and other engine inputs. This parameter is accurate to within 20 N·m (15 lb ft) of actual measured engine torque.
Gear Ratio | -- | Ratio, Varies | This parameter displays the actual transmission gear ratio. The scan tool displays the gear ratio calculated from the automatic transmission input shaft speed sensor (AT ISS) and the automatic transmission output shaft speed sensor (AT OSS) inputs.
Ignition Voltage | -- | Volts, 12-14 | This parameter displays the system voltage measured at the ignition feed.
Last Shift Time | -- | Seconds, Varies | This parameter displays the actual time of the last upshift. This value is only accurate if the shift was adaptable.
PC Sol. Actual Current | -- | Amps, Varies | This parameter displays the actual current flow through the pressure control solenoid circuit which is measured by the control module. High current flow results in low line pressure. Low current flow results in high line pressure.
PC Sol. Duty Cycle | -- | %, Varies | This parameter displays the commanded state of the pressure control solenoid expressed as a percentage of energized ON time. A reading of low percent indicates zero ON time, non energized, or no current flow. A high percent at idle indicates maximum ON time, energized, or high current flow.
PC Sol. Ref. Current | -- | Amps, Varies | This parameter displays the commanded current of the pressure control solenoid circuit. High current results in low line pressure. Low current results in high line pressure.
TCC Brake Switch | -- | Closed | This parameter displays the status of the TCC brake switch circuit input. OPEN indicates a zero voltage input, brake pedal applied. CLOSED indicates a voltage input, brake pedal released. The scan tool displays OPEN or CLOSED.
TCC Duty Cycle | -- | %, Varies | This parameter displays the commanded percentage of ON time for the TCC PWM solenoid. A high percentage represents an ON, energized, commanded state. 0 percent represents an OFF, non-energized, commanded state.
TCC Duty Cycle CKT Status | -- | OK | This parameter displays the solenoid driver feedback voltage signal and displays the circuit status on the scan tool. If the voltage is low when the solenoid is commanded OFF, the scan tool will display Open/Short to GND. If the voltage is high when the solenoid is commanded ON, the scan tool will display Short to Volts. If no circuit fault is present the scan tool will display OK.
TCC Enable Sol. | -- | Off | This parameter displays 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. The scan tool displays Yes or No.
TCC Enable Sol. CKT Status | -- | OK | This parameter displays whether an open or short to ground or voltage exist in TCC solenoid valve feedback signal. If the TCC solenoid is commanded OFF the scan tool will display open or short to ground. If the TCC solenoid is commanded ON the scan tool will display short to voltage. If no circuit fault is present the scan tool will display OK.
TCC Slip Speed | -- | RPM, Varies | This parameter displays 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. | -- | Park/Neutral | This parameter 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. If a valid combination of inputs is not detected, invalid will be displayed.
TFP Sw. A/B/C | -- | HI/LOW/HI | This parameter 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. LOW represents a zero voltage signal. HI represents an ignition voltage signal.
TP Indicated Angle | -- | %, Varies | This parameter displays the desired throttle angle for operating conditions present at the time.
TR Sw. | -- | Park/Neutral | This parameter displays the decoded status of the four A/B/C/P inputs from the transmission range switch. The scan tool displays Park, Reverse, Neutral Drive, Intermediate, Low, and Invalid. If a valid combination of inputs is not detected, invalid will be displayed.
TR Sw. A/B/C/P | -- | LOW/HI/HI/LOW | This parameter displays the status of the four inputs from the transmission range switch. The scan tool displays HI/LOW. HI indicates an ignition voltage input to the control module. LOW indicates a zero voltage input to the control module.
Trans. Fluid Temp. | -- | °C (°F), Varies | This parameter displays the input signal of the transmission fluid temperature sensor. Transmission fluid temperature is high 151°C (304°F) when signal voltage is low, 0 volt, and transmission fluid temperature is low -40°C (-40°F ) when signal voltage is high, 5 volt.
Transfer Case Ratio | -- | Ratio, Varies | This parameter displays the ratio of the transfer case calculated by engine speed divided by transmission output speed based on transmission commanded gear.
Transmission Hot Mode | -- | Off | This parameter displays the automatic transmission fluid temperature (TFT) and displays On or Off. 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 than 5 seconds. These numbers are approximate. They differ with transmissions.
Transmission ISS | -- | RPM, Varies | This parameter displays the rotational speed of the transmission input shaft. The scan tool displays input shaft speed is revolutions per minute (RPM).
Transmission OSS | -- | RPM, Varies | This parameter displays the rotational speed of the transmission output shaft. The scan tool displays output shaft speed as revolutions per minute (RPM). On four-wheel drive applications, the transfer case output shaft speed is measured.
Vehicle Speed | -- | km/h (mph), Varies | This parameter displays the speed at which the vehicle is traveling. The scan tool displays vehicle speed as kilometers per hour (km/h), miles per hour (MPH). The vehicle speed is calculated based on the input signal from the automatic transmission output shaft speed sensor.

#### Scan Tool Output Controls

Output Control | Description
--- | ---
1-2 Solenoid |

• | The powertrain control module (PCM) commands the 1-2 shift solenoid valve ON and OFF. The scan tool 1-2 Sol. parameter should match the commanded state. The scan tool Commanded Gear parameter should correspond with the shift solenoid combination. Refer to Shift Solenoid Valve State and Gear Ratio table.

• | When the ignition is ON, and the engine is OFF, there are no limits to this control. The solenoid remains ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

• | When the engine is running, the following control limits apply:

- | Only sequential gear changes are allowed. For example, 1st to 3rd is not allowed. If a non-sequential gear change is attempted, the message "Non-sequential gear changes not allowed. Gear changes must be in order" appears on the scan tool display.

- | The vehicle speed must be below a calibrated value. If the vehicle speed is too high, the message "Vehicle speed too high" appears on the scan tool display.

- | The engine speed must be below a calibrated value. If the engine speed is too high, the message "Engine speed too high" appears on the scan tool display.

- | Downshifts are allowed only when the vehicle speed is below a calibrated value. If the vehicle speed is too high, the message "Eng. is on and veh. speed too hi for 3-2 or 2-1 downshift" appears on the scan tool display.

- | The gear requested may not be greater than the current selected transmission range (PRNDL). For example, 3rd gear is not allowed if the transmission range is D2. If the gear requested is greater than the current selected transmission range, the message "Eng. running and gear request is greater than the current TR" appears on the scan tool display.

- | The solenoid remains ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

2-3 Solenoid |

• | The PCM commands the 2-3 shift solenoid valve ON and OFF. The scan tool 2-3 Sol. parameter should match the commanded state. The scan tool Commanded Gear parameter should correspond with the shift solenoid combination. Refer to Shift Solenoid Valve State and Gear Ratio table.

• | When the ignition is ON, and the engine is OFF, there are no limits to this control. The solenoid will remain ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

• | When the engine is running, the following control limits apply:

- | Only sequential gear changes are allowed. For example, 1st to 3rd is not allowed. If a non-sequential gear change is attempted, the message "Non-sequential gear changes not allowed. Gear changes must be in order" appears on the scan tool display.

- | The vehicle speed must be below a calibrated value. If the vehicle speed is too high, the message "Vehicle speed too high" appears on the scan tool display.

- | The engine speed must be below a calibrated value. If the engine speed is too high, the message "Engine speed too high" appears on the scan tool display.

- | Downshifts are allowed only when the vehicle speed is below a calibrated value. If the vehicle speed is too high, the message "Eng. is on and veh. speed too hi for 3-2 or 2-1 downshift" appears on the scan tool display.

- | The gear requested may not be greater than the current selected transmission range (PRNDL). For example, 3rd gear is not allowed if the transmission range is D2. If the gear requested is greater than the current selected transmission range, the message "Eng. running and gear request is greater than the current TR" appears on the scan tool display.

- | The solenoid remains ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

3-2 Downshift Solenoid |

• | The PCM commands the 3-2 shift solenoid valve ON and OFF. The scan tool 3-2 Downshift Sol. parameter should match the commanded state.

• | When the ignition is ON, and the engine is OFF, there are no limits to this control. The solenoid remains ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

• | When the engine is running, the following control limits apply:

- | The transmission range (PRNDL) must be in Park or Neutral. If the transmission range is not in Park or Neutral, the message "Engine running and transmission range is not Park/Neutral" appears on the scan tool display.

- | The solenoid remains ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

Clear TAP (Transmission Adaptive Pressures) |

• | The PCM clears, or resets, the TAP cells to the original base value.

• | There are no limits to using this output control. It may be performed with the engine running or when the ignition is ON, and the engine is OFF.

PC Solenoid |

• | The PCM commands the amperage, current, to the pressure control solenoid in order to control transmission line pressure. As the amperage increases, the line pressure decreases. As the amperage decreases, the line pressure increases. The amperage range is 0.00-1.10 and may be commanded in one-tenth amp increments.

• | When the ignition is ON, and the engine is OFF, the reference, commanded, amperage may be controlled within calibrated limits. The scan tool parameter "PC Sol. Ref. Current" changes but the parameter "PC Sol. Actual Current" does not change. The reference current remains until commanded otherwise.

• | When the engine is running, the following control limits apply:

- | When the transmission range is Park or Neutral, the reference, commanded, amperage may be controlled within calibrated limits. The engine speed must be less than 2,500 RPM. If the engine speed is greater than 2,500 RPM, the message "TR in park/neutral and engine speed over 2,500 RPM" appears on the scan tool display. Both the scan tool parameters "PC Sol. Ref. Current" and "PC Sol. Actual Current" change. Both current readings remain until commanded otherwise.

- | When the transmission range is not in Park or Neutral, the reference amperage can only be controlled less than the current determined by the PCM. The PCM does not allow a value to be selected that may cause damage to the transmission. If the requested amperage is more than allowed by the PCM, the message "Requested current for the PC Solenoid is too high" appears on the scan tool display.

- | Transmission range DTCs must not be active. If a transmission range DTC is active, the message "Engine running with transmission DTC present" appears on the scan tool display.

Preset Transmission Adapts | Important: Depending on the application, this procedure may set some or all Transmission Adaptive values to zero. This procedure will clear the current Transmission Shift Adaptives to preset engineered values.
Shift Transmission |

• | The PCM commands upshifts and downshifts. The scan tool Commanded Gear parameter should correspond with the shift solenoid combination. Refer to Shift Solenoid Valve State and Gear Ratio table.

• | When the ignition is ON, and the engine is OFF, there are no limits to this control. The scan tool shift solenoid states change to match the Commanded Gear selected.

• | When the engine is running, the following control limits apply:

- | The PCM does not allow a shift if it causes the engine RPM to exceed a calibrated limit. If a gear is requested and the engine speed is too high, the message "Engine speed too high" appears on the scan tool display.

- | The PCM does not allow a 3-2 or 2-1 downshift if the vehicle speed exceeds a calibrated limit. If either downshift is requested and the vehicle speed is too high, the message "Eng. is on and veh. speed too hi for 3-2 or 2-1 downshift" appears on the scan tool display.

- | The PCM does not allow a 4-3 downshift if the vehicle speed exceeds a calibrated limit. If a 4-3 downshift is requested and the vehicle speed is too high, the message "Vehicle speed too high" appears on the scan tool display.

- | The PCM does not allow an upshift if the vehicle speed exceeds a calibrated limit. If an upshift is requested and the vehicle speed is too high, the message "Vehicle speed too high" appears on the scan tool display.

- | The PCM does not allow an upshift that is greater than the current selected transmission range (PRNDL). For example 3rd gear is not allowed if the transmission range is D2. If an upshift is requested that is greater than the current selected transmission range, the message "Eng. running and gear request is greater than the current TR" appears on the scan tool display.

Torque Converter Clutch (TCC) Control Solenoid |

• | The PCM commands the duty cycle of the TCC pulse width modulation (PWM) solenoid. The duty cycle is represented by a percentage of ON, energized, time. Approximately 90-100 percent duty cycle represents an ON, energized, commanded state. Zero percent represents an OFF, non-energized, commanded state. The scan tool TCC Duty Cycle parameter should match the commanded state.

• | When the ignition is ON, and the engine is OFF, there are no limits to this control. The solenoid remains ON, 90-100 percent duty cycle, until commanded OFF, zero percent duty cycle, and vice versa. When the output control is exited, the solenoid duty cycle is determined by the PCM.

• | When the engine is running, the following control limits apply:

- | If the transmission range is Park, and the transmission is in hot mode, the TCC control solenoid may not be commanded OFF. If the solenoid is requested OFF, the message "TCC OFF command disabled in Hot Mode" appears on the scan tool display.

- | The TCC control solenoid may not be commanded OFF for more than a calibrated amount of time. If the solenoid is commanded OFF for a certain amount of time, the message "TCC OFF time has been exceeded" appears on the scan tool display.

TCC Enable |

• | The PCM commands the TCC enable solenoid valve ON and OFF. The scan tool TCC Enable parameter should match the commanded state.

• | When the ignition is ON, and the engine is OFF, there are no limits to this control. The solenoid remains ON until commanded OFF, and vice versa. When the output control is exited, the solenoid state is determined by the PCM.

• | When the engine is running, the following control limits apply:

- | If the transmission range is Park or Neutral, the TCC enable solenoid may not be commanded OFF for more than a calibrated amount of time. If the solenoid is commanded OFF for a certain amount of time, the message "TCC OFF time has been exceeded" appears on the scan tool display.

- | If the transmission range is Park or Neutral and the TCC control solenoid duty cycle is less than maximum capacity, the TCC enable solenoid may not be commanded ON. If the solenoid is requested ON during these conditions, the message "TCC Control Solenoid is not set to maximum Pressure" appears on the scan tool display.

- | If the TCC control solenoid duty cycle is less than maximum capacity, the TCC enable solenoid may not be commanded ON. If the solenoid is commanded ON during these conditions the message "TCC Control Solenoid is not set to maximum Pressure" appears on the scan tool display.

- | If the transmission is in hot mode, the TCC enable solenoid may not be commanded OFF. If the solenoid is requested OFF the message "TCC OFF command disabled in Hot Mode" appears on the scan tool display.