Scan Tool Data Definitions

ENGINE CONTROL MODULE DATA DESCRIPTIONS
A list of explanations for each message displayed on the Tech 1 scan tool begins below. This information will assist in diagnosing driveability and emissions malfunctions, since the displays can be viewed while driving the vehicle.

ENGINE SPEED- Range: 0 - 9999 RPM
Engine speed is calculated by the Engine Control Module (ECM) from the ignition reference pulses it receives from the Camshaft Position (CMP) sensor. The ECM will keep this value close to the desired idle under various engine loads with the engine idling.

DESIRED IDLE - Range: 0 - 2000 RPM
The desired idle speed is an ECM requested speed. The ECM determines what this speed should be from the information it receives from various sensors throughout the vehicle.

ENG COOL TEMP - Range: -40°C - 120°C /-40°F - 250°F
The Engine Coolant Temperature (ECT) sensor is a thermistor (a variable resistor that changes with temperature) in series with a fixed resistor in the ECM. The ECM provides a 5 volt reference voltage to the ECT sensor. The ECM reads the voltage across the ECT sensor and calculates this voltage reading into a temperature reading. A low voltage reading at the ECM indicates a hot engine and a high voltage reading at the ECM indicates a cold engine.

MASS AIR FLOW
The Mass Air Flow (MAF) sensor measures the amount of air which passes through it in a given amount of time. The ECM uses this information to determine the operating condition of the engine to control fuel delivery. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle. As the amount of air entering the sensor increases, then so does the sensor signal current to the ECM. As air flow decreases, then so does the signal current to the ECM.

THROT POSITION - Range: 0 - 5.10 VOLTS
The Throttle Position (TP) sensor has a potentiometer whose resistance changes with the throttle valve position. The ECM provides a 5 volt reference voltage to the TP sensor. The ECM reads the voltage across the TP sensor and converts it into throttle position. When the TP sensor resistance decreases (throttle valve opening increases), the voltage being monitored at the ECM increases. When the TP sensor resistance increases (throttle valve opening decreases), the voltage being monitored at the ECM decreases.

THROTTLE ANGLE - Range: - 0 - 90°
The throttle angle parameter displays the throttle position in degrees. The Tech 1 will display "0" when the throttle valve is fully closed, and will display about "8O" when the throttle valve is fully opened.

HO2S - Range: 0 - 1250 mV
The Heated Oxygen Sensor (HO2S) is the primary input to the fuel delivery system. The ECM monitors the HO2S voltage, when the system is in "Closed Loop" operation. When the voltage reading is high, the air/fuel mixture is rich, and when the voltage reading is low the air/fuel mixture is lean. Under normal operating conditions, the voltage reading should constantly fluctuate.

S.T. FUEL TRIM - Range: 0 - 255
This value represents the short term corrections to the air/fuel mixture computation. A value of 128 indicates that no correction is necessary. A value below 128 indicates a lean condition, and a value above 128 indicates an enrichment condition.

LT. FUEL TRIM - Range: 0 - 255
This value represents the long term corrections to the air/fuel mixture computation. A value of 128 indicates that no correction is required. A value below 128 indicates a lean condition, and a value above 128 indicates an enrichment condition.

SPARK ADVANCE - Range: -10° - 60°
This displays the ECM controlled value that is being used to control the spark timing.

INJ. PULSE WIDTH - Range: 0 - 65 mSEC
This value is the amount of time, in milliseconds, that the ECM is commanding the fuel injector to stay on during combustion. A shorter on time yields a leaner air/fuel mixture, and a longer on time yields richer air/fuel mixture.

ISC AIR FLOW - Range: 0 - 250 L/MIN
This parameter represents the quantity of the bypass airflow through the Idle Air Control (IAC) valve.

IDLE SWITCH - Range: Tech 1 displays "ON" or "OFF"
This parameter indicates the throttle valve position. The Tech 1 will display "ON" when the throttle valve is fully closed, and will display "OFF" when it is opened.

FUEL PUMP - Range: Tech 1 displays "ON" or "OFF"
The Tech 1 displays "ON" when the fuel pump is running. The fuel pump will run for approximately 3 seconds when the ignition switch is turned to "ON," during this time the Tech 1 will display "ON." After 3 seconds the fuel pump will stop and the Tech 1 will display "OFF." When the engine is started, the fuel pump will run as long as the ECM is receiving a Camshaft Position (CMP) sensor signal from the distributor (Tech 1 display is "ON.").

EGR GAS TEMP - Range: 0°C - 240°C/32°F - 470°F
This parameter is used to measure the temperature of the exhaust gases that flow into the intake manifold. The Engine Control Module (ECM) uses this temperature reading to determine when to energize and de-energize the Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve, thus controlling the amount of exhaust gases that flow into the intake manifold.

EGR SOLENOID - Range: Tech 1 displays "ON" or "OFF"
This parameter displays the status of the Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve. When the Tech 1 displays "ON," the EGR SV valve is energized, thus allowing exhaust gases to flow into the intake manifold. When the Tech 1 displays "OFF," the EGR SV valve is de-energized, forbidding any exhaust gasses to flow into the intake manifold.

A/C SWITCH - Range: Tech 1 displays "ON" or "OFF"
This parameter displays the status of the A/C system. If the A/C has been requested (A/C switch "ON"), the Tech 1 will display "ON." If the A/C has not been requested (A/C switch "OFF"), the Tech 1 will display "OFF." The ECM will use this information to increase engine idle speed, when required.

POWER STEERING SW - Range: Tech 1 displays "ON" or "OFF"
This indicates whether the steering is being assisted by the power steering pump. The Tech 1 will display "ON" when the front wheels are turned all the way to the right or left. When the need for assisted steering no longer exists, the Tech 1 will display "OFF."

PARK/NEUTRAL POS - Range: Tech 1 displays "P-N- -" or "-R-DL"
This parameter displays the manual selector's position with vehicles equipped with an automatic transaxle. When the manual selector is in the "P" or "N" position, the Tech 1 will display "P-N- -." When the manual selector is in the "R," "D," "2" or "L" position, the Tech 1 will display "-R-DL." On vehicles equipped with a manual transaxle, the Tech 1 will always display "-R-DL."

MPH km/h - Range: 0 - 200 km/h 0 - 125 MPH
This parameter displays the vehicle speed. The ECM receives reference pulses from the Vehicle Speed Sensor (VSS) and converts them into km/h and MPH for display.

FUEL EVAP PURGE - Range: 0-100%
An Evaporative Emission (EVAP) canister is used to capture the gas vapors emitted from the fuel tank. When the ECM energizes the EVAP canister purge valve, the fumes are allowed to flow into the intake manifold and Tech 1 will display "ON." When the ECM determines that there is no longer a need for the gas vapors in the intake manifold, the ECM will de-energize the EVAP canister purge valve, and the Tech 1 will display "OFF."

RICH/LEAN STATUS - Range: Tech 1 displays "RICH" or "LEAN"
This parameter displays the status of the oxygen concentration in the air/fuel mixture. When the Heated Oxygen Sensor voltage is high, the Tech 1 displays "RICH," and when the HO2S voltage is low, the Tech 1 will display "LEAN."

SYSTEM VOLTAGE - Range: 0 - 18.75 VOLTS
This value is the system voltage reading that is detected at the ECM.

CHARGING EFFI - Range: 0 - 100%
The Tech 1 displays "CHARGING EFFI" in percent. This is the rate of efficiency at which the charging system is operating. Factors taken into consideration for this percentage are engine speed, electrical load and engine load.