Scan Tool Data Definitions
TECH 1 DATA DEFINITIONSENGINE 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.
INTAKE AIR TEMP - Range: -40°C - 120°C/-40°F - 250°F
The Intake Air Temperature (IAT) sensor is a thermistor (a variable resistor that changes with temperature) in a series with a fixed resistor in the ECM. The ECM provides a 5 volt reference voltage to the IAT sensor. The ECM reads the voltage across the IAT sensor and calculates this voltage reading into a temperature reading to control the air/fuel mixture and spark timing. A low voltage reading at the ECM indicates that the intake air is warm and a high voltage reading at the ECM indicates that the intake air is cold.
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.
MAP - Range: 0 - 125 kPa/0 - 5.10 V
The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure. This change in pressure, that results from engine load and RPM changes, is converted into a voltage reading that is monitored by the ECM. A low voltage reading at the ECM indicates low manifold pressure, and a high voltage reading at the ECM indicates high manifold pressure.
MAP - Range: 0 - 125 kPa/0 - 5.10 V
The BARO reading displayed is measured from the MAP sensor at ignition switch "ON," engine "OFF" and WOT conditions. The BARO reading displayed represents barometric pressure and is used to compensate for altitude.
HO2S - Range: 0 - 2500 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.
HO2S ACTIVATION - Range: Tech 1 displays "ACTIVATE" or "DEACTIVATE"
The Tech 1 displays "ACTIVATE" when the system enters "Closed Loop" operation. This indicates that the HO2S is hot enough for the ECM to control fuel delivery. When the Tech 1 displays "DEACTIVATE" the system is in "Open Loop" operation. This indicates that the HO2S is cold and the ECM bases fuel delivery on throttle position and manifold absolute pressure.
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.
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 an enleanment 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 an enleanment condition, and a value above 128 indicates an enrichment condition.
IAC/ISC DUTY - Range: 0 - 100%
The idle Speed Control (ISC) motor opens and closes the throttle valve according to signals from the ECM. The ECM controls the time in which the ISC motor is activated to adjust the idle speed (open and close the throttle plate).
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.
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: Tech 1 displays "ON" or "OFF"
This represents the Evaporative Emissions Canister Purge valve. The ECM commands the EVAP Canister Purge valve "ON" under several conditions. The scan tool will display "ON"/"OFF." If the vehicle is at operating temperature, the EVAP Canister Purge valve should be "OFF" at idle.
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.
ELECTRIC LOAD - Range : Tech 1 displays "ON" or "OFF"
This mode displays the status of the light switch, blower speed selector switch and the rear defogger switch. If one or more of the previously mentioned switches is "ON," a signal is sent to the ECM to increase engine idle speed due to the increased electronic load.
IAC/ISC DUTY - Range: 0 - 100%
The idle Speed Control (ISC) motor opens and closes the throttle valve according to signals from the ECM. The ECM controls the time in which the ISC motor is activated to adjust the idle speed (open and close the throttle plate).
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 Engine Control Module (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."
SYSTEM VOLTAGE - Range: 0 - 18.75 VOLTS
This value is the system voltage reading that is detected at the ECM.
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 HO2S voltage is high, the Tech 1 will display "RICH," and when the HO2S voltage is low, the Tech 1 will display "LEAN."