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 should remain close to desired idle under various engine loads with the engine idling.
TP Angle: Scan Tool Range 0-100%. The scan tool displays the amount of throttle opening in percentage. At closed throttle the scan tool displays 11% and at wide open throttle (WOT) the scan tool displays near 80%.
ECT: Scan Tool Range -40°C to 120°C (-40°F to 250°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.
IAT: Scan Tool Range -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.
MAP: Scan Tool Range 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. 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.
Engine Load: Scan tool range 0-100%. This parameter indicates engine load based on manifold absolute pressure. The higher the percentage, the more load the engine is under.
Base PWM Cyl #1: This parameter indicates the amount of time the fuel injector solenoid valve is open.
IAC Duty Cycle: The parameter indicates the opening of the by-pass air passage in terms of percentage. The opening of the by-pass air passage determines the amount of air flowing through the by-pass air passage and is controlled by the IAC motor.
Engine Speed at Misfire: This parameter represents the engine RPM at the moment that the misfire DTC was set.
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.
Misfire Current Cyl #1, #2, #3, #4: Indicates a count of the abnormal engine revolutions (misfire) for each cylinder.
Ign. Cycle Counter: This parameter indicates the total number of times the ignition coils fire for every 1,000 engine revolutions.
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 1000 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.
Short Term FT: The scan tool displays a positive or a 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. 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. Fuel trim values at maximum authority may indicate an excessively rich or lean system.
Long Term FT: The scan tool displays a positive or a negative percentage. The PCM derives the Long Term Fuel Trim from the Short Term Fuel Trim value. The Long Term Fuel Trim represents a long-term correction of fuel delivery. A value of 0% indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0% indicates that the fuel system is rich and the PCM is reducing the fuel delivery (decreased fuel injector pulse width). A positive value significantly greater than 0% indicates that a lean condition exists and the PCM compensates by adding fuel (increased fuel 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 from the Short Term Fuel Trim value. The Long Term Fuel Trim represents a long-term correction of fuel delivery. A value of 0% 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 the fuel delivery (decreased fuel injector pulse width). A value significantly greater than 128 indicates that a lean condition exists and the PCM compensates by adding fuel (increased fuel injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.
Total Fuel Trim: Total Fuel Trim is a calculated value obtained by putting Short Term Fuel Trim and Long Term Fuel Trim together. The Total Fuel Trim value indicates how large a correction is necessary in order to keep the air/fuel mixture at the stoichiometrical 14.7:1 ratio. Total Fuel Trim values greater than .50 counts indicates that the PCM is adding fuel (increasing fuel injector pulse width). Total Fuel Trim values less than .50 counts indicates that the PCM is reducing fuel (decreasing fuel injector pulse width).
Diagnostic Mode: Indicates whether the vehicle's diagnostics are operating in Normal Mode, or in Check Mode.
HO2S 1 L/R Response Time: The scan tool displays in milliseconds, the time it takes the HO2S 1 to switch from lean to rich.
HO2S 1 R/L Response Time: The scan tool displays in milliseconds, the time it takes the HO2S 1 to switch from rich to lean.
Decel Fuel Mode: The Decel Fuel Mode parameter indicates when the PCM is operating the fuel injectors in the fuel cutoff mode (the output to the fuel injector is stopped). When the fuel cutoff mode is active the Decel Fuel Mode parameter should read Active. The Decel Fuel Mode parameter should read Inactive during all other fueling conditions.
Loop Status: The Loop Status parameter will display one of the following conditions:

• | OPEN LOOP: The engine has not met all conditions to go into Closed Loop.

• | CLOSED LOOP: The PCM is using the oxygen sensors as feedback for fuel control.

Spark: Scan tool range -1 to 60 degrees. The scan tool displays the PCM controlled value that is being used to control the spark timing.
EVAP Pressure Switching Solenoid: This parameter indicates when the powertrain control module (PCM) is turning ON the EVAP pressure switching solenoid. The EVAP pressure switching solenoid determines which vacuum signal goes to the fuel tank pressure sensor.
Vehicle Speed: Scan tool range 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.
TCC Solenoid: This parameter indicates when the PCM is requesting the TCC On for the 4-spd automatic transmission.
PNP: This parameter indicates the range selection of the automatic transmission. 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.
TCC Brake Switch: 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.
Electrical Load: This mode displays the status of the head lamp switch, and the rear defogger switch. If one or more of the previously mentioned switches is ON, a signal is sent to the PCM to increase the engine idle speed due to the increase load.
A/C Switch: This parameter indicates whether the A/C switch on the I/P has been selected.
Command A/C: The parameter indicates On whenever the PCM allows the A/C compressor clutch to engage.
Starter Switch: This parameter displays On when the PCM is receiving a signal indicating that the engine starter motor is cranking.
Fuel Pump: This parameter indicates whether the PCM is requesting the fuel pump On or Off.
Powertrain DTC: Indicates the number of diagnostic trouble codes (DTCs) that are set.
MIL Requested DTC: This parameter will indicate whether the MIL is illuminated due to a DTC being set.