The Engine Scan Tool Data Definitions contains a brief description of all engine related parameters available on the scan tool.

AC Relay Command: The parameter indicates ON whenever the powertrain control module (PCM) allows the A/C compressor clutch to engage.

AC Request Signal: This parameter indicates whether the A/C switch on the instrument panel (IP) has been selected.

Cam Phase Angle Actual: This parameter indicates the actual camshaft advance in relative degrees. The displayed value is calculated from CMP sensor and CKP sensor inputs. Normal Cam Phase Angle readings are 0 to 4 degrees, where each single degree displayed is approximately equal to 5 degrees of actual camshaft advance.

Cam Phase Angle Desired: This parameter indicates the desired camshaft advance in relative degrees. The PCM determines the desired advance in camshaft timing. On a normal engine this reading will be the same as the Cam Phase Angle.

Cam Phase Angle Variance: This parameter indicates the difference between the Cam Phase Angle and the Cam Phase Angle Desired. This value can be displayed in positive or negative degrees.

Camshaft Phase Solenoid DC: The scan tool range is 0-100 percent. This parameter displays the duty cycle (DC) of the CMP actuator solenoid valve. A reading of less than 20 percent indicates the PCM is retarding camshaft timing. A reading of 20 to 40 percent indicates the PCM is holding the camshaft timing at the current setting. A reading of more than 40 percent indicates the PCM is advancing camshaft timing.

Camshaft Phase Solenoid Command: This parameter indicates whether the powertrain control module (PCM) is controlling the camshaft position (CMP) actuator solenoid valve. The scan tool will display Active when the PCM is commanding the CMP actuator solenoid. A CMP actuator solenoid that is in an Active mode is not necessarily advancing the camshaft phase. Only about 50 percent of the CMP actuator solenoid movement results in advancement of the camshaft phase.

Decel Fuel Cut-off: The Decel Fuel Mode parameter indicates when the powertrain control module (PCM) is operating the fuel injectors in the fuel cut-off mode, the output to the fuel injector is stopped. When the fuel cut-off mode is active the Decel Fuel Mode parameter should read Active. The Decel Fuel Mode parameter should read Inactive during all other fueling conditions.

Diagnostic Mode: Indicates whether the vehicle's diagnostics are operating in Normal mode or in Check mode.

ECT Sensor: The scan tool range is -40 to +140°C (-40 to +284°F). The engine coolant temperature (ECT) sensor is a thermistor which changes internal resistance as the temperature changes. When the sensor is cold, internal resistance high, the powertrain control module (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 the engine load based upon the 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 powertrain control module (PCM) computes engine speed from the ignition reference pulses. The engine speed should remain close to the 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 diagnostic trouble code (DTC) was set.

EVAP Purge Solenoid: This parameter indicates when the evaporative emission (EVAP) canister purge solenoid valve is ON.

Fuel Pump Relay Command: This parameter indicates whether the powertrain control module (PCM) is requesting the fuel pump ON or OFF.

Fuel Tank Pressure Sensor: The scan tool range is -31.0 to +16.5 mm Hg (-16.6 to +8.9 in H2O). This parameter indicates the pressure in the fuel tank and is expressed with respect to the barometric pressure (BARO) When the fuel tank pressure is equal to the barometric pressure, the scan tool indicates 0 mm Hg.

High Electrical Load: This mode displays the status of the headlamp switch and the rear defogger switch. If one or more of the switches is ON, a signal is sent to the powertrain control module (PCM) to increase the engine idle speed due to the increased load.

HO2S 1: The scan tool range is 0-1275 mV. The heated oxygen (HO2S) 1 parameter represents the fuel control exhaust oxygen sensor output voltage. The voltage should fluctuate constantly within a range of 10 mV, lean exhaust, and 1000 mV, rich exhaust, while operating in Closed Loop.

HO2S 1 L/R Response Time: The scan tool displays the amount of time the heated oxygen sensor 1 (HO2S 1) requires to switch from lean to rich in milliseconds.

HO2S 1 R/L Response Time: The scan tool displays the amount of time the heated oxygen sensor 1 (HO2S 1) requires to switch from rich to lean in milliseconds.

HO2S 2: The scan tool range is 0-1275 mV. The rear heated oxygen sensor 2 (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.

IAC Motor Command: This parameter indicates the opening of the bypass air passage in percent. The amount of air flowing through the bypass air passage is controlled by the idle air control (IAC) valve and determines engine idle speed. The IAC valve is pulse width modulated (PWM) by the powertrain control module (PCM) and the duty cycle range is 0-100 percent.

IAT Sensor: The scan tool range is -40 to +140°C (-40 to +284°F). The powertrain control module (PCM) converts the resistance of the intake air temperature (IAT) 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.

Ign. Cycle Counter: This parameter indicates the total number of times the ignition coils fire for every 1,000 engine revolutions.

Injector #1 Command: This parameter indicates the amount of time the fuel injector solenoid valve is open.

Load at Misfire: This is Freeze Frame data stored when a misfire is detected by the powertrain control module (PCM). Load at Misfire is the engine load at which the misfire was set, measured in grams per revolutions.

Long Term FT: The scan tool displays a positive or a negative percentage. The powertrain control module (PCM) derives the Long Term fuel trim (FT) from the Short Term fuel trim value. The Long Term fuel trim represents a long-term correction of fuel delivery. A value of 0 percent indicates that the fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A negative value significantly less than 0 percent indicates that the fuel system is rich and the PCM is reducing the fuel delivery, decreasing the fuel injector pulse width. A positive value significantly more than 0 percent indicates that a lean condition exists and the PCM compensates by adding fuel, increasing fuel injector pulse width. Fuel trim values at maximum authority may indicate an excessively rich or lean system.

Loop Status: The Loop Status parameter will display one of the following conditions: OPEN LOOP: The engine has not met all of the conditions necessary for Closed Loop operation. CLOSED LOOP: The powertrain control module (PCM) is using the oxygen sensors as feedback for fuel control.

MAF Sensor: The scan tool range is 0.0-200 g/s. This parameter indicates the quantity of air entering the engine through the mass air flow (MAF) sensor. This volume of air is measured in grams per second (g/s).

MIL Command: This parameter will indicate whether the malfunction indicator lamp (MIL) is illuminated due to a diagnostic trouble code (DTC) being set.

Misfire Current Cyl #1, #2, #3, #4: Indicates a count of the abnormal engine revolutions (misfire) for each cylinder.

Number of DTC(s): Indicates the number of diagnostic trouble codes (DTCs) that are set.

PNP Switch: This parameter indicates the range selection of 3 speed or 4 speed automatic transmission equipped vehicles. The parameter will display Park/Neutral for the Park or Neutral position of the gear selector. The parameter will display In Gear for the Reverse, Drive, or Low positions of the gear selector.

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 powertrain control module (PCM). The Short Term FT correction is driven by the fuel control oxygen sensor voltage. When the oxygen sensor (O2S) voltage remains less than 450 mV the PCM adds fuel and the Short Term FT parameter displays a positive percentage. When the oxygen sensor voltage stays at more than 450 mV the PCM subtracts fuel and the Short Term FT parameter displays a negative percentage. During an extended idle in high ambient temperatures the evaporative emission (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.

Spark: The scan tool range is -1 to +60 degrees. The scan tool displays the powertrain control module (PCM) controlled value that is being used to control the spark timing.

Starter Switch: This parameter displays ON when the powertrain control module (PCM) is receiving a signal indicating that the engine starter motor is cranking.

TCC Brake Pedal Switch: This parameter is used only on 4 speed automatic transmission equipped vehicles. When the brake pedal is applied, the torque converter clutch (TCC) brake switch sends a signal to the powertrain control module (PCM) in order to disengage the TCC.

TCC Enable Solenoid Command: This parameter is used only on 4 speed automatic transmission equipped vehicles. The TCC Enable Solenoid Command indicates when the powertrain control module (PCM) is requesting the torque converter clutch (TCC) ON.

Total Fuel Trim: Total Fuel Trim is a calculated value obtained by combining the Short Term FT and the Long Term FT 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 of + or - 25 percent indicate a fuel system that is operating near the limits of normal fuel control. Total Fuel Trim data is useful in diagnosing fuel system concerns and DTC P0171 or DTC P0172.

Total Misfire Current Count: Indicates a count of the total misfires for all the cylinders.

TP Sensor: The scan tool range is 0-100 percent. The scan tool displays the amount of throttle opening in percentage. At closed throttle the scan tool displays 8-12 percent. At wide open throttle (WOT) the scan tool displays approximately 80 percent.

Vehicle Speed Sensor: 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 the pulses into km/h and mph for display.