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 alphabetical order.

A/C Relay Command: The parameter will indicate on whenever the A/C idle-up signal is received by the powertrain control module (PCM) from the A/C compressor control module. This will allow the PCM to adjust the engine idle to maintain acceptable engine performance.
BARO: The scan tool range 0-125 kPa. The barometric pressure (BARO) sensor measures the changes in atmospheric pressure. This parameter will read approximately 95 to 105 kPa at sea level.
Battery Voltage: This parameter indicates battery positive voltage inputted from the main relay to the PCM.
Calculated IAC Air Flow: The calculated idle air control (IAC) air flow is the volume of air the PCM determines is necessary to maintain the desired engine idle speed. The PCM uses information from the TP sensor, the MAF sensor, and the engine speed in order to calculate the required IAC valve pintle position. The scan tool displays the volume of air in liters per minute (L/Min) or cubic feet per minute (FT3/Min).
CMP Active Counter: The scan tool range is 0-255 counts. When the CMP sensor is supplying engine reference signals to the PCM, the scan tool will indicate an increasing count. The count value will increase from 0 counts to as high as 255 counts, and then roll-over back to 0 counts.
Decel. Fuel Cutoff Signal: When the fuel is being cut, output signal to the fuel injector is stopped, the parameter should read on, but when fuel is not in the cut off mode the parameter should read OFF.
Desired Idle Speed: The desired idle speed is a PCM internal parameter which indicates the PCM requested idle speed. If the engine is not running, this number indicated is not valid.
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.
ECT Sensor: The scan tool range is -40°C to +120°C (-40°F to +250°F). The engine coolant temperature (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 0-100 percent. This parameter indicates engine load based on manifold absolute pressure. The higher the percentage, the more load the engine is under.
EVAP Density Trim: The scan tool range is 0-128 counts. This parameter indicates evaporative emission (EVAP) system purge concentration and is indicated in counts.
EVAP Duty Cycle: The scan tool range is 0-100 percent. The EVAP duty cycle specifies the EVAP canister purge valve on (valve open) time rate within a certain set cycle. Zero percent means that the purge valve is completely closed while a 100 percent is a fully open valve.
EVAP Tank Pressure Control Solenoid: The EVAP tank pressure control solenoid valve is open when the valve is turned on by the PCM and closed when the valve is turned off.
EVAP Vent Solenoid Command: This parameter indicates when the PCM is turning on the EVAP canister vent solenoid. The scan tool indicates Not Venting when the solenoid is turned ON.
EVAP Purge Solenoid Command: The scan tool range is 0-100 percent. This parameter indicates when the PCM is turning on the EVAP canister purge solenoid. The EVAP canister purge solenoid is controlled by the PCM using a PWM signal. Zero percent means that the solenoid is completely closed. One hundred percent indicates a fully open solenoid.
EGR Solenoid Command: The scan tool range is 0-100 percent. The exhaust gas recirculation (EGR) duty cycle specifies the EGR valve on (valve open) time rate within a certain set cycle. Zero percent means that the valve is completely closed. One hundred percent indicates a fully open valve.
Fan Request: This parameter indicates the status of the PCM command to the A/C Condenser fan relay. The PCM turns ON the A/C condenser fan relay when the A/C is operating. The PCM also turns ON the relay when the ECT sensor indicates that the engine coolant temperature is more than 110°C (230°F).
Fuel Level Sensor: The scan tool range is 0-100 percent. This parameter indicates approximate fuel level in the fuel tank. The detectable range of the fuel level sensor is set as 0 to 100 percent, however, with some models whose fuel tank capacity is smaller, the indicated fuel level may be only 70 percent even when the fuel tank is full.
Fuel Pump Relay Command: 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 CMP sensor.
Fuel Tank Pressure: The scan tool range is -60.0 to +61.5 mmHg. This 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 mmHg.
High Electrical Load: This parameter indicates the status of rear window defogger circuit. The PCM increases the idle speed in order to compensate for the additional load on the engine. The High Electrical Load parameter will display a Yes when the rear defogger is turned ON.
HO2S 1: The scan tool range is 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 1000 mV (rich exhaust) while operating in closed loop.
HO2S 2: The scan tool range is 0-1275 mV. The rear heated oxygen sensor (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.
HO2S 1: A YES display indicates that the oxygen sensor is warmed up and is capable of sending useful voltage readings to the PCM. A NO display indicates a cold or not ready oxygen sensor.
HO2S 2: A YES display indicates that the oxygen sensor is warmed up and is capable of sending useful voltage readings to the PCM. A NO display indicates a cold or not ready oxygen sensor.
IAC Motor Command: The scan tool range is 0-100 percent. This scan tool parameter indicates the opening of the bypass air passage in terms of percentage. The opening of the bypass air passage determines the amount of air flowing through the bypass air passage and is controlled by the IAC motor.
IAT Sensor: The scan tool range is -40°C to +120°C (-40°F 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.
Injector 1 Command: This parameter indicates the time of the fuel injector valve opening.
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 percent indicates that fuel delivery requires no compensation in order to maintain the desired air/fuel ratio. A negative value, significantly below 0 percent, 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 percent, 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.
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 the MAF sensor inputs.
MAF Sensor: This parameter indicates the quantity of air entering the engine through the MAF sensor. This volume of air is measured in grams per second (g/s).
MAP Sensor: The scan tool range is 0-125 kPa/0.0-5.0 volts. The 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.
PNP Switch: The scan tool displays Park/Neutral when the transmission is in Park or Neutral, and In Gear when the transmission is operating in forward or reverse gears.
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 signal enables the PCM to adjust the engine idle in order to maintain acceptable engine performance.
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.
Spark: The scan tool range is -1 to +60 degrees. This displays the PCM controlled value that is being used to control the spark timing.
Starter Switch: This parameter displays Cranking when the PCM is receiving a signal indicating that the engine starter motor is cranking. The scan tool will display Released when the ignition is on and when the engine is running.
Total Fuel Trim Average: The value of total fuel trim is obtained by putting the values of short term fuel trim and long term fuel trim together. This value indicates how much correction is necessary in order to keep the air/fuel mixture at the stoichiometrical 14.7:1 ratio.
TP Sensor: The scan tool displays 0-5 volts/0-100 percent. The scan tool displays the amount of throttle opening in volts. Closed throttle displays about 1 volt or 0 percent. Wide open throttle (WOT) displays about 3.5 volts or 100 percent.
TCC Brake Pedal Switch: When the brake pedal is depressed, the torque converter clutch (TCC) brake switch sends a signal to the PCM. The PCM will then disengage the TCC.
Vehicle Speed Sensor: The scan tool range is 0-200 km/h (0-125 mph). This parameter displays the vehicle speed. The PCM receives reference pulses from the vehicle speed sensor (VSS) and converts them into km/h and mph for display.