For 1990-2009 cars

The Transmission and the Engine Scan Tool Data Definitions contains a brief description of all transmission and engine related parameters available on the scan tool. The list is arranged in the alphabetical order.

A/C Switch: This parameter indicates whether the A/C switch is on the I/P has been selected.
Command A/C: This parameter indicates On whenever the PCM allows the A/C compressor clutch to engage.
Diagnostic Mode: Indicates whether the vehicle's diagnostics are operating in Normal Mode, or in Check Mode.
ECT: The Scan tool range is 80-90°C (176-194°F). The ECT sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold/internal resistance high, the PCM monitors a high signal voltage and interprets the voltage as a cold engine. As the sensor warms/internal resistance decreases, the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.
Engine Load: The scan tool range is 19.7 percent to 43.9 percent. This parameter indicates engine load based on manifold absolute pressure. The higher the percentage, the more load the engine is under.
Engine Speed: The scan tool range is 0-10,000 RPM. The PCM computes Engine speed from the ignition reference pulses. The Engine speed should remain close to desired idle under various engine loads with the engine idling.
Engine Speed at Misfire: This parameter represents the engine RPM at the moment that the misfire DTC was set.
Fuel Pump: This parameter indicates that the PCM is turning on the fuel pump by turning on the fuel pump relay. The PCM will turn the fuel pump relay ON for three seconds when the ignition is turned on and turn the fuel pump relay on continuously when receiving reference pulses from the ignition module.
IAT: The scan tool range is -40 to +120°C (-40 to +250°F). The PCM converts the resistance of the intake air temperature sensor to degrees. The PCM uses the intake air temperature (IAT) in order to adjust fuel delivery and spark timing according to incoming air density.
Load at Misfire: Freeze Frame Data stored when a misfire is detected by the PCM. Engine load at which the misfire was set, measured in grams per revolutions.
Loop Status: The scan tool displays Open Loop or Closed Loop. Closed Loop indicates that the PCM is controlling fuel delivery according to oxygen sensor voltage. Open Loop indicates that the PCM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered ON the TP sensor, the ECT sensor, and MAP sensor inputs.
MAP: The scan tool range is 0-145 kPa/0.0-6.99 volts. The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure from engine load, and speed changes. As intake manifold pressure increases, the intake vacuum decreases resulting in a higher kPa reading.
MIL Request By DTC: This parameter will indicate whether the MIL is illuminated due to a DTC being set.
Overdrive: The scan tool displays ON/OFF, when the overdrive switch is applied.
PNP: The scan tool displays P-N when the transmission is in Park or Neutral, and R-D-L when the transmission is operating in forward or reverse gears.
Powertrain DTC: Indicates the number of diagnostic trouble codes (DTCs) that are set.
Shift Request: This parameter is the actual shift time of the last upshift.
Starter Switch: This parameter displays On when the PCM is receiving a signal indicating that the engine starter motor is cranking.
TCC Brake Solenoid: When the brake pedal is applied, the torque converter clutch (TCC) brake switch sends a signal to the PCM in order to disengage the TCC.
TCC Solenoid: This parameter indicates when the PCM is requesting the TCC On for the 4-speed automatic transmission.
TP Angle: The scan tool Range 0-10,000 RPM. The PCM computes Engine speed from the ignition reference pulses. The engine speed should remain close to desired idle under various engine loads with the engine idling.
Vehicle Speed: The scan tool range is 0-200 km/h/0-125 MPH. This parameter displays the vehicle speed. The Powertrain Control Module (PCM) receives reference pulses from the Vehicle Speed Sensor (VSS) and converts them into km/h and MPH for display.