For 1990-2009 cars

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

Engine Speed: The scan tool range is 0-10,000 RPM. The PCM computes engine speed from ignition reference pulses. The Engine Speed parameter should remain close to the Desired Idle Speed parameter when the engine is warm and idling.
Desired Idle Speed: The Desired Idle Speed is a programmed value thadetermines PCM requested idle speed. The Desired Idle Speed parameter is not valid while cranking the engine
ECT: The scan tool range is -40°C to 120°C (-40°F to 250°F). The ECT sensor is a thermistor. The PCM monitors the voltage on the ECT sensor signal circuit. When the ECT sensor is cold (internal resistance high), the PCM sees a high signal voltage. The signal voltage and the internal resistance of the sensor decrease as the engine becomes warm. The scan tool displays default values of -40°C or -40°F when there is an open in the ECT sensor signal circuit.
IAT: The scan tool range is -40°C to 120°C (-40°F to 250°F). The IAT sensor is a thermistor. The PCM monitors the voltage on the IAT sensor signal circuit. When the IAT sensor is cold (internal resistance high), the PCM sees a high signal voltage. The signal voltage and the internal resistance of the sensor decrease as the engine becomes warm. The scan tool displays default values of -40°C or -40°F when there is an open in the IAT sensor signal circuit.
Engine Load: The scan tool range is 0% to 100%. The Engine Load parameter is calculated form manifold vacuum readings. The higher the Engine Load percentage, the greater the load on the engine.
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. The scan tool displays MAP sensor input as pressure (kPa) or voltage. When the MAP sensor signal circuit is open, the scan tool MAP sensor voltage display can read as high as 6.99 volts. This is caused by the scan tool software and should be considered normal. The actual signal circuit voltage is 4.9-5.0 volts.
BARO: The scan tool range is 0-125 kPa. The barometric pressure (BARO) sensor measures the changes in atmospheric pressure. The BARO parameter is approximately 95 to 105 kPa at sea level.
TP Sensor: The scan tool range is 0.0 -5.0 volts. The TP sensor parameter indicates the amount of throttle opening in volts. The TP Sensor display is near 1 volt when the throttle is closed (normal idle). The TP sensor display is near 3.5 volts when the throttle is wide open.
TP Angle: The scan tool range is 0-100%. The TP Angle parameter displays the amount of throttle opening as a percentage. The TP Angle display is near 13% when the throttle is closed (normal idle). The TP Angle display is near 100% when the throttle is wide open.
IAC Duty Cycle: The scan tool range is 20% to 40%. The IAC Duty Cycle parameter indicates the opening of the idle air (bypass) passage as a percentage. The IAC Duty Cycle percentage will increase when the PCM commands a larger idle air passage opening. The IAC Duty Cycle percentage will decrease when the PCM commands a smaller idle air passage opening.
Closed Throttle Switch: The Closed Throttle Switch parameter displays Idle when the throttle valve is closed, and Not Idle when the throttle valve is open. The Closed Throttle Switch parameter is an output of the PCM that is calculated from TP sensor input.
HO2S 1: The scan tool range is 0-1275 mV. The HO2S 1 parameter represents the fuel control HO2S output voltage. When operating in Closed Loop, the HO2S 1 voltage should fluctuate between 10 mV (lean exhaust) and 1000 mV (rich exhaust).
HO2S 2: The scan tool range is 0-1275 mV. The rear HO2S 2 indicates the oxygen content of the exhaust exiting the catalytic converter. A normal warm HO2S 2 output voltage will be inactive or appear to be lazy. When the engine is operating in Closed Loop, the HO2S 2 voltage will be stable between 100 mV and 900 mV.
Loop Status: The scan tool displays Open Loop or Closed Loop. Closed Loop indicates that the PCM is controlling fuel delivery according to feedback (input) from the oxygen sensor. Open Loop indicates that the PCM is ignoring the oxygen sensor input. In Open Loop the PCM bases fuel delivery on input from the TP sensor, the ECT sensor, and the MAP sensor.
HO2S 1 Ready: A Yes display indicates that the PCM has recieved oxygen sensor voltage readings significantly above and below the threshold value. A No display indicates an inactive oxygen sensor.
HO2S 2 Ready: A Yes display indicates that the PCM has recieved oxygen sensor voltage readings significantly above and below the threshold value. A No display indicates an inactive oxygen sensor.
Short Term FT: The scan tool display is a positive or negative percentage. The Short Term Fuel Trim (FT) represents a short term correction to fuel delivery by the PCM. The Short Term FT correction is driven by the fuel control oxygen sensor. When the oxygen sensor voltage remains below 450 mV the PCM adds fuel and the Short Term FT parameter displays a positive percentage. When the oxygen sensor voltage stays above 450 mV the PCM subtracts fuel and the Short Term FT parameter displays a negative percentage. During an extended idle with high ambient temperatures, the EVAP canister may purge, causing the Short Term FT to read in the negative range. This is a normal condition. The fuel trim values at maximum authority may indicate an excessively rich or lean condition.
Short Term FT: The scan tool display is counts. The Short Term Fuel Trim (FT) represents a short term correction to the PCM controlled fuel delivery. The Short Term FT correction is driven by the fuel control oxygen sensor. When the oxygen sensor voltage remains below 450 mV the PCM adds fuel and the Short Term FT parameter is greater than 128. When the oxygen sensor voltage stays above 450 mV the PCM subtracts fuel and the Short Term FT parameter is less than 128. During an extended idle with high ambient temperatures, the EVAP canister may purge, causing the Short Term FT to read less than 128. This is a normal condition. The fuel trim values at maximum authority may indicate an excessively rich or lean condition.
Long Term FT: The scan tool display is a positive or negative percentage. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long term correction in the fuel delivery. A value of 0% indicates that fuel delivery requires no compensation in order to maintain the desired air/fuel ratio. A negative value, significantly below 0%, indicates that the fuel system is rich. When the fuel system is rich, the PCM reduces fuel delivery by decreasing injector pulse width. A positive value, significantly greater than 0%, indicates that a lean condition exists. During a lean condition the PCM increases fuel delivery by increasing injector pulse width. Fuel trim values at maximum authority may indicate an excessively rich or lean condition.
Long Term FT: The scan tool display is counts. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long-term correction in the fuel delivery. A value of 128 counts indicates that fuel delivery requires no compensation in order to maintain the desired air/fuel ratio. A value significantly less than 128 indicates that the fuel system is rich. When the fuel system is rich, the PCM reduces fuel delivery by decreasing injector pulse width. A value significantly greater than 128 indicates that a lean condition exists. During a lean condition the PCM increases fuel delivery by increasing injector pulse width. Fuel trim values at maximum authority may indicate an excessively rich or lean condition.
Total Fuel Trim: The scan tool range is a positive or negative percentage. The value Total Fuel Trim is obtained by putting values of Short Term FT and Long Term FT together. The Total Fuel Trim value indicates how much correction is necessary to keep the air/fuel mixture at the stoichiometrical 14.7:1 ratio.
Injector PWM: The Injector PWM parameter indicates the amount of time the fuel injector solenoid valve is open. The longer the Injector PWM time, the more fuel is delivered.
Fuel Cutoff Signal: The Fuel Cutoff Signal parameter indicates when the PCM is operating the fuel injector in the fuel cutoff mode. When the engine is operating in the fuel cutoff mode, fuel injector output is stopped. When the fuel cutoff mode is active the Fuel Cutoff Signal parameter will indicate ON. The Fuel Cutoff Signal parameter should indicate OFF during all other fuel modes.
Spark: The scan tool range is -1 degree to 60 degrees. The Spark parameter indicates the amount of ignition system spark advance.
Spark Advance Adjust Test Switch: When the duty check data link connector Test Switch Terminal (terminal 5) is grounded, the Spark Advance Adjust Test Switch parameter will display On. Grounding the duty check data link connector Test Switch Terminal causes the ignition timing to be fixed at the base setting.
EVAP Duty Cycle: The scan tool range is 0- 100%. The EVAP Duty Cycle parameter specifies the amount of time the EVAP canister purge valve ON (open). 0% indicates that the EVAP canister purge valve is fully closed. 100% indicates that the EVAP canister purge valve is fully open.
EVAP Vent Solenoid: The EVAP Vent Solenoid parameter indicates when the PCM is turning ON the EVAP canister vent solenoid.
EVAP Density Trim: The scan tool range is 0 to 128 counts. The EVAP Density Trim parameter indicates EVAP system purge concentration and is indicated in counts.
Fuel Level: The scan tool range is 0 to 100%. The Fuel Level parameter indicates the approximate fuel level in the fuel tank. The indicated fuel level may be only 90% even when the fuel tank is FULL.
Fuel Tank Pressure: The scan tool range is -60.0 to 61.5 mm Hg. The Fuel Tank Pressure parameter indicates the pressure in the fuel tank and is expressed with respect to the barometric pressure. When the fuel tank pressure is equal to the barometric pressure, the scan tool indicates 0.0 mm Hg.
EVAP Tank Pressure Control Solenoid: The EVAP Tank Pressure Control Solenoid parameter indicates whether the EVAP tank pressure control solenoid valve is On or Off. When the PCM commands the EVAP tank pressure control solenoid valve ON, the solenoid will be in an OPEN position. When the PCM commands the EVAP tank pressure control solenoid valve OFF the solenoid will be in a CLOSED position. The scan tool will display On or Off to indicate whether the EVAP tank pressure control solenoid valve is open or closed.
Air Conditioning: The Air Conditioning parameter will indicate On whenever the A/C idle-up signal is received by the PCM from the A/C compressor control module. The A/C idle-up signal enables the PCM to adjust the engine idle in order to maintain acceptable engine performance.
Engine Coolant Fan: The Engine Coolant Fan parameter will display an On signal whenever the PCM is turning the cooling fan relay ON.
Fuel Pump: The Fuel Pump 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 two to three seconds when the ignition is turned ON. The PCM will turn the fuel pump relay ON continuously when receiving reference pulses from the ignition module.
Power Steering Switch: The scan tool will display an On signal whenever the steering wheel is turned right or left far enough to increase the power steering fluid pressure above a specified amount. This will allow the PCM to adjust the engine idle to maintain acceptable engine performance.
Starter Switch: The Starter Switch parameter displays On when the PCM is receiving a signal indicating that the engine starter motor is cranking.
Battery Voltage: The Battery Voltage parameter specifies the battery positive voltage that was input from the Main Relay to the PCM.
Electrical Load Signal: The Electrical Load Signal parameter will display On whenever certain electrical loads are indicated to the PCM. The electrical load signal enables the PCM to adjust the engine idle in order to maintain acceptable engine performance.
PNP: This parameter indicates the automatic transmission range selection. The parameter will display P - N for the park or neutral position of the gear selector and R - D - L for the reverse, drive or low positions of the gear selector.
Vehicle Speed: The scan tool range is 0-200 km/h / 0-125 MPH. The Vehicle Speed parameter displays the vehicle's road speed. The PCM receives reference pulses from the vehicle speed sensor (VSS) and converts the pulses into km/h and MPH for display.