Scan Tool Data Definitions
ECM DATA DESCRIPTIONA list of explanations for each data message displayed on the Tech 1 scanner begins below.
This information will assist in tracking down emission or driveability problems, since the displays can be viewed while the vehicle is being driven.
With the Tech 1 scanner connected to the Data Link Connector (DLC), the traction control system may be disabled and the "traction control" light may turn "ON."
ENGINE SPEED - Range 0-9999 RPM - Engine speed is computed by the Engine Control Module (ECM) from the fuel control reference input. it should remain close to desired idle under various engine loads with engine idling.
DESIRED IDLE - Range 0-3175 RPM - The idle speed that is commanded by the ECM. The ECM will compensate for various engine loads to keep the engine at the desired idle speed.
ENGINE COOL TEMP - Range -40° to 199°C, -40° to 389°F- The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal will decrease and the ECM will interpret the lower voltage as a warm engine.
INTAKE AIR TEMP - Range -40° to 199°C, -40° to 389°F -The ECM converts the resistance of the intake air temperature sensor to degrees. intake Air Temp (IAT) is used by the ECM to adjust fuel delivery and spark timing according to incoming air density.
MAP - Range 11 - 105 kPa/0.00 - 5.10 volts - The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure which results from engine load and speed changes. As intake manifold pressure increases, the air density also increases and additional fuel is required.
BARO - Range 11-105 kPa/0.00 - 5.10 Volts - The Barometric Absolute Pressure (BARO) reading displayed is measured from the MAP sensor at key "ON," engine "OFF" and Wide Open Throttle (WOT) conditions. The BARO reading displayed represents barometric pressure and is used to compensate for altitude differences.
THROT POSITION - Range 0 - 5.10 Volts - Used by the ECM to determine the amount of throttle demanded by the driver. Should read 0.30 - 1.00 volt at idle to above 4 volts at wide open throttle.
THROTTLE ANGLE - Range 0-100% - Computed by the ECM from Throttle Position (TP) sensor voltage should read 0% at idle, 100% at Wide Open Throttle (WOT).
SHORT TERM FUEL TRIM - Range 0-255 - Short term fuel trim represents a short term correction to fuel delivery by the ECM in response to the amount of time the oxygen sensor voltage spends above or below the 450 mV threshold. If the oxygen sensor voltage has mainly been below 450 mV, indicating a lean air/fuel mixture, short term fuel trim will increase to tell the ECM to add fuel. If the oxygen sensor voltage stays mainly above the threshold, the ECM will reduce fuel delivery to compensate for the indicated rich condition.
LONG TERM FUEL TRIM - Range 0-255 - Long term fuel trim is derived from the short term fuel trim value and is used for long term correction of fuel delivery. A value of 128 counts indicates that fuel delivery requires no compensation to maintain a 14.7:1 air/fuel ratio. A value below 128 counts means that the fuel system is too rich and fuel delivery is being reduced (decreased injector pulse width). A value above 128 counts indicates that a lean condition exists and the ECM is compensating by adding fuel (increased injector pulse width).
OXYGEN SENSOR - Range 0-1132 mV - Represents the exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 10 mv (lean Exhaust) and 1000 mV (Rich exhaust) when operating in "Closed Loop."
LOOP STATUS - Tech 1 Scanner Displays "OPEN" or "CLOSED""Closed Loop" displayed indicates that the ECM is controlling fuel delivery according to oxygen sensor voltage. In "Open Loop," the ECM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on TP, ECT, and MAP sensor inputs only.
INJECTOR PULSE WIDTH - Tech 1 Scanner Range 0.10 to 999.9 - Indicates in milliseconds the time the injectors remain "ON." When engine load is increased, injector pulse width will increase.
AIR FUEL RATIO - Range 0-25.5 represents the mixture of air and fuel required to receive optimal fuel economy, emissions and engine performance (14.7 to 1). A lower number indicates a richer commanded air fuel mixture while a higher number indicates leaner commanded air fuel mixture.
FUEL TRIM CELL - Range 0-15 - Fuel trim cell is dependent upon engine speed and MAP sensor readings. A plot of RPM vs MAP is broken into 16 cells. Fuel trim cell indicates which cell is currently active.
FUEL TRIM ENABLE - Tech 1 Scanner Displays "NO" or "YES"If the fuel trim enable system is learning (YES) the fuel trim is responding to the short term fuel trim. If fuel trim reads "NO" then fuel trim will not respond to changes in short term fuel trim.
KNOCK RETARD - Range 0° to 45° - Indicates the amount of spark advance the ECM is removing from Ignition Control (IC) in response to the Knock Sensor (KS) signal.
KNOCK SIGNAL - Tech 1 Scanner Displays "YES" or "NO" - Indicates whether or not a knock signal is being detected by the ECM. Should display "NO" at idle.
SPARK ADVANCE - Tech 1 Scanner Range - 90° to 90° - This is a display of the spark advance (IC) calculation which the ECM calculates and then provides all spark advance to the ignition system. The ECM computes the desired spark advance using data such as engine temperature, RPM, load, vehicle speed, and operating mode. There is no adjustment for spark advance.
IDLE AIR CONTROL - Range 0-255 - Displays the commanded position of the idle air control pintle in counts. The higher the number of counts, the greater the idle air passages opened. Idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM.
PARK NEUTRAL POS - Tech 1 Scanner Displays -P-N-- or -R-DL - P-N-- displayed indicates that the gear select lever is in park or neutral.
VEHICLE SPEED - Range 0-255 km/h, 0-159 MPH - The vehicle speed sensor signal is converted into km/h and mph for display.
EXHAUST RECIRCULATION - Range 0 to 100 % - The ECM cycles the Exhaust Gas Recirculation (EGR) solenoid valve "ON" and "OFF." The "ON" time (duty cycle) of the EGR solenoid valve, expressed as a percent, determines how much the exhaust gas is recirculated.
FUEL EVAP PURGE - Tech 1 Scanner Range 0-100% - Used to control canister purge function. 0% implies the valve is commanded fully closed while 100% implies that the valve is fully open.
SYSTEM Volts - Range 0 to 25.5 Volts - Tech 1 scanner indicates the battery voltage detected at the ECM ignition input.
FUEL PUMP VOLTS - Range 0 to 25.5 Volts - ECM monitors fuel pump voltage to compensate fuel delivery in the event of low voltage.
AIR SYSTEM - Tech 1 Scanner displays "ON"/"OFF" - When the ECM enables the AIR system, Tech 1 scanner should indicate "ON." When the ECM disables the AIR system, Tech 1 scanner should indicate "OFF."
POWER STEERING - Tech 1 Scanner Displays NORMAL/HIGH PRESS - With no power steering load, the Tech 1 scanner should indicate normal. When power steering pressure Is high, scan should indicate high pressure. When high power steering pressure is indicated, the A/C clutch will be disabled.
A/C MONITOR - Displays "OK"/"Not OK" - When the A/C system has adequate refrigerant charge (but not overcharged), ignition voltage is supplied to the ECM through the high pressure switch and pressure cycling switch. The ECM should indicate "A/C Monitor" as "OK." If a low or high pressure condition is indicated, the signal would not be supplied to the ECM. Therefore, the ECM would disable the A/C compressor clutch and the Tech 1 scanner would indicate "A/C Monitor" as "Not OK."
A/C REQUEST - Tech 1 Scanner Displays "YES" or "NO" - Represents if the A/C request from the control head is being received by the ECM.
A/C Clutch - Tech 1 Scanner Displays "ON" or "OFF" - Represents the command state of the A/C clutch control relay. Clutch should be engaged when "ON" is displayed.
OIL LIFE MONITOR - Tech 1 scanner displays the percentage of oil life, before the next service interval is required.
FAN 1/FAN 2 - When the ECM commands the coolant fans "ON," the Tech 1 scanner display will switch from "OFF" to "ON" (without V08 option).
PASS-KeyII - An input from the Central Control Module (CCM) that tells the ECM to enable the injectors if the proper signal is received. The Tech I scanner will normally display "Enabled." If the PASS-KeyII test has failed, the display will switch to "Disabled" and the fuel system may be disabled.
QUAD-DRIVER MODULE - Tech 1 Scanner displays FAULT "YES"/"NO" - Quad-driver modules are used to power the EGR, Evaporative Emissions System (EVAP) canister and AIR Injection Reaction (AIR) systems. The Tech 1 scanner should display "NO" and switch to YES" if a QDM circuit becomes opened, shorted, or grounded and a Diagnostic Trouble Code (DTC) 26 will set.
TORQUE CONV CL - Tech 1 Scanner Displays "OFF" or "ON" - The Tech 1 scanner only indicates when the ECM has enabled the [1][2]Torque Converter Clutch (TCC) driver, but this does not confirm that the TCC has engaged. To determine if TCC is operating properly, engine RPM should decrease when TCC is enabled.
4th GEAR SWITCH - Tech 1 Scanner Displays "YES"/"NO" - This switch is used by the ECM to modify TCC lock and unlock points, when in a down shift maneuver. When the transmission shifts into 4th gear the scan will indicate "YES."
CALIBRATION ID - Range 0 to 9999 - The Programmable Read Only Memory (PROM) identification describes the particular PROM being used in the ECM. The Tech 1 scanner display number is not the service part number.
TIME FROM START - Range 0:00:00 to 18:12:15 HR/MIN/SEC - A measure of how long the engine has been running. When the engine stops, it is reset to zero.