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: Scan Tool Range 0-10,000 RPM. The PCM computes engine speed from the ignition reference pulses. The Engine Speed parameter should remain close to Desired Idle Speed parameter when the engine is warm and the idling.
Desired Idle Speed: The Desired Idle Speed is a PCM internal parameter that indicates the PCM requested idle. The Desired Idle Speed parameter is not valid if the engine is not running.
ECT: Scan Tool Range -40°C to 120°C (-40°F to 250°F). The ECT sensor is a thermistor that changes internal resistance as temperature changes. The PCM monitors a high signal voltage when the sensor is cold (internal resistance high) and interprets that voltage as a cold engine. The voltage signal decreases as the sensor becomes warm (internal resistance decreases) and the PCM interprets the lower voltage as a warm engine.
IAT: Scan Tool Range -40°C to 120°C (-40°F to 250°F). The PCM displays the electrical resistance of the intake air temperature sensor (IAT) as degrees. The PCM uses the IAT sensor in order to calculate incoming air density. The PCM uses air density information in order to adjust fuel delivery and ignition timing.
Engine Load: Scan tool range 0 percent to 100 percent. The Engine Load parameter indicates engine load based on manifold absolute pressure. The higher the Engine Load percentage, the greater load the engine is under.
MAP: Scan Tool Range 0-125 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. The scan tool MAP sensor voltage display can read as high as 6.99 volts when the MAP sensor signal circuit is open. 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: Scan Tool Range 0-110 kPa. The barometric pressure (BARO) Sensor measures the changes in atmospheric pressure. The BARO parameter will read approximately 95 to 105 kPa at sea level.
TP Sensor: The scan tool displays 0.0-5.0 volts. The TP Sensor parameter displays the amount of throttle opening in volts. The TP Sensor display is near 1 volt when the throttle is closed (normal idle) and the TP Sensor display is near 3.5 volts when the throttle is wide open.
TP Angle: The scan tool displays 0-100 percent. The TP Angle parameter displays the amount of throttle opening as a percentage. The TP Angle display is near 13 percent when the throttle is closed (normal idle) and the TP Angle display is near 100 percent when the throttle is wide open.
ISC Duty Cycle: Scan Tool Range 20 percent to 40 percent. The ISC Duty Cycle parameter indicates the opening of the throttle valve by the ISC actuator in a measurement of a percentage. The ISC Duty Cycle percentage will increase when the PCM commands a larger throttle valve opening. The ISC Duty Cycle percentage will decrease when the ISC actuator responds to a PCM command for a smaller throttle valve opening.
Closed Throttle Switch: The Closed Throttle Switch parameter will read Idle when the throttle valve is closed, and Not Idle when the throttle valve is opened. The closed throttle position (CTP) switch is part of the idle speed control (ISC) motor.
HO2S 1: Scan Tool Range 0-1275 mV. The HO2S 1 parameter represents the fuel control exhaust oxygen sensor output voltage. The voltage should fluctuate constantly within a range between 10 mV (lean exhaust) and 1 000 mV (rich exhaust) while operating in Closed Loop.
HO2S 2: Scan Tool Range 0-1275 mV. The rear HO2S 2 represents the exhaust oxygen output voltage beyond the catalytic converter. This voltage will remain inactive or appear lazy within a range 100 mV (lean exhaust) and 900 mV (rich exhaust) when the system is operating in Closed Loop.
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.
HO2S 1 Ready: A Yes display indicates that the oxygen sensor is warmed up and is capable of sending useful voltage readings to the PCM. No display indicates a cold (not ready) oxygen sensor.
HO2S 2 Ready: A yes display indicates that the oxygen sensor is warmed up and is capable of sending useful voltage readings to the PCM. No display indicates a cold (not ready) oxygen sensor.
Short Term FT: The scan tool displays 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 voltage. 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 system.
Short Term FT: The scan tool displays counts. 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 voltage. When the oxygen sensor voltage remains below 450 mV the PCM adds fuel and the Short Term FT parameter displays a count greater than 128. When the oxygen sensor voltage stays above 450 mV the PCM subtracts fuel and the Short Term FT parameter displays a count less than 128. During an extended idle with high ambient temperatures, the EVAP canister may purge causing the Short Term FT to read lower than 128. This is a normal condition. The fuel trim values at maximum authority may indicate an excessively rich or lean system.
Long Term FT: The scan tool displays 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 percent indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0 percent indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A positive value significantly greater than 0 percent indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.
Long Term FT: The scan tool displays 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 of fuel delivery. A value of 0 percent indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A value significantly below 128 indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A value significantly greater than 128 indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.
Total Fuel Trim: The scan tool displays a positive or negative percentage. The value of the 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 stoichiometrical 14.7:1 ratio.
Injector PWM: The Injector PWM parameter indicates the amount of time of the fuel injector solenoid valve is open.
Fuel Cutoff Signal: The Fuel Cutoff Signal parameter indicates when the PCM is operating the fuel injector in the fuel cutoff mode (the output to the fuel injector is stopped). When the fuel cutoff mode is active the Fuel Cutoff Signal parameter should read ON. The Fuel Cutoff Signal parameter should read OFF during all other fuel modes.
Spark: Scan tool range -1 degree to 60 degrees. The Spark parameter displays the PCM controlled value that is being used in order to control the spark timing.
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: Scan tool range 0-100 percent. The EVAP Duty Cycle parameter specifies the amount of time the EVAP canister purge valve ON (open). 0 percent indicates that the EVAP canister purge valve is fully closed. 100 percent 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: Scan tool range 0 to 128 counts. The EVAP Density Trim parameter indicates EVAP system purge concentration and is indicated in counts.
Fuel Level: Scan tool range 0 to 100 percent. The Fuel Level parameter indicates the approximate fuel level in the fuel tank. The indicated fuel level may be only 90 percent even when the fuel tank is FULL.
Fuel Tank Pressure: Scan tool range -60.0 to 61.5 mmHg. 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 mmHg.
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.
EGR Sol. Vacuum Valve: The EGR Sol. Vacuum Valve parameter indicates when the PCM is turning ON the EGR solenoid vacuum valve.
EGR Bypass Valve: The EGR Bypass Valve parameter indicates when the PCM is turning ON the EGR bypass solenoid
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.
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.
Vehicle Speed: Scan tool range 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.