Scan Tool Data Definitions

ENGINE SPEED TECH 1 RANGE 0-9999 RPM - Engine speed is computed by the ECM from the fuel control reference input. it should remain close to desired idle under various engine loads with engine idling.

DESIRED IDLE - TECH 1 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 speed.

ENG COOL TEMP - TECH 1 RANGE -40°C TO 199°C, -40°F TO 389°F - The ECM converts the resistance of the engine coolant temperature sensor to degrees.

LOOP STATUS - TECH 1 STATES 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 sensor, engine coolant temp., and MAF sensor inputs only. "Closed Loop"operation should begin when the O2S becomes active, and coolant temperature exceeds 50°C (122°F) for more than 30 seconds.

HROT POSITION - TECH 1 RANGE 0-5.10 VOLTS - Used by the ECM to determine the amount of throttle demanded by the driver. Should read 0.2-0.74 volt at idle to above 4 volts at wide open throttle.

THROTTLE ANGLE - TECH 1 RANGE 0-100% - Computed by the ECM from TP sensor voltage (Throt position). Should read 0% at idle. 100% at wide open throttle.

O2S - TECH 1 RANGE 0-1096 mV - Represents the exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 100 mV (Lean exhaust) and 1000 mV (Rich exhaust) when operating in "Closed Loop."

INJ PULSE WIDTH - TECH 1 RANGE 0-999.9 ms - Indicates the length of time the ECM is commanding the injectors "ON" for each injector duty cycle. A longer "ON" time indicates a richer commanded mixture.

O2S CROSS COUNTS - TECH 1 RANGE 0-255 - The number of times the oxygen sensor voltage crosses over the rich/lean threshold since the last data transmission to the scan tool.

AIR FUEL RATIO - TECH 1 RANGE 0.00-99.99 - The reading reflects the commanded value. This should be at or near 14.7. A lower number indicates a richer commanded air fuel mixture while a higher number indicates a leaner mixture.

RICH/LEAN STATUS - TECH 1 STATES RICH OR LEAN - Indicates whether exhaust oxygen sensor voltage is above (rich) or below (lean) the 450 mV oxygen sensor threshold voltage. Should change constantly at idle, indicating that the ECM is controlling the air/fuel mixture properly.

ALTITUDE - TECH 1 STATES "YES" OR "NO" - "YES" displayed indicates that the engine is operating at high altitude, and the ECM is altering fuel delivery and spark advance to compensate.

MASS AIR FLOW - TECH 1 RANGE 0-255.9 GM/SEC - The ECM converts the mass air flow sensor input signal into grams per second, indicating the rate of airflow entering the engine.

CALC. ENG. LOAD - TECH 1 RANGE 0-255 - Engine load is calculated by the ECM by engine speed and mass airflow. Should increase with an increase in RPM or airflow.

SPARK ADVANCE TECH 1 RANGE .900 TO 900 - This is a display of the spark advance (ignition control) calculation which the ECM is programming into the ignition system. It computes the desired spark advance using data such as; engine temperature, RPM, load, vehicle speed, and operating mode.

S. T. FUEL TRIM - TECH 1 RANGE 0-255 - S. T. 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, S. T. 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 or the indicated rich condition. Under certain conditions such as extended idle, canister purge may cause S. T. fuel trim to read less than 100 counts.

L. T. FUEL TRIM - TECH 1 RANGE 0-255 - L. T. fuel trim is derived from the S. T. fuel trim value and is used for long-term correction of fuel delivery. A value of 128 counts indicates that fuel delivery is at the proper rate to maintain a 14.7:1 air/fuel ratio and no correction is needed. 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). L. T. fuel trim tends to follow S. T. fuel trim; a value of less than 100 counts due to canister purge at idle should not be considered unusual.

FUEL TRIM CELL - TECH 1 RANGE 0-15 - Fuel trim cell is dependent upon engine speed and either manifold air pressure or mass air flow readings. A plot of RPM vs MAF is broken into 16 cells. Fuel trim cell indicates which cell is currently active.

KNOCK RETARD - TECH 1 RANGE 0°-90° - Indicates the amount of spark advance the ECM is removing from ignition control in response to the knock sensor signal. Should read 0° at idle.

KNOCK SIGNAL - TECH 1 STATES "YES" OR "NO" - Indicates whether or not a knock signal is being detected by the ECM. Should read "NO" at idle.

IDLE AIR CONTROL - TECH 1 RANGE 0-255 - Displays the commanded position of the idle air control pintle in counts. The higher the number of counts, the greater the commanded idle speed. Idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM.

PARK/NEUTRAL POS - TECH 1 STATES P-N OR -R-D-L - Represents the park/neutral position switch input to the ECM.

VEHICLE SPEED - TECH 1 RANGE 0-159 mph, 0-255 Km/h - The vehicle speed sensor signal is converted into Km/h and mph for display. Should closely match speedometer reading.

TORQUE CONV CL - TECH 1 STATES "ON" OR "OFF" - "ON" displayed indicates that the TCC solenoid has been commanded "ON" by the ECM; however, actual TCC operation depends upon the integrity of the system.

SYSTEM VOLTAGE - TECH 1 RANGE 0-25.5 VOLTS - This represents the system voltage measured by the ECM at the ignition 1 feed.

FUEL EVAP PURGE - TECH 1 RANGE 0-100% - A proportional signal used to control EVAP canister purge function. 0% indicates that the valve is commanded fully closed while 100% implies that the valve is fully open.

AC LEARNED - TECH 1 STATES "YES" OR "NO" - Indicates whether or not the ECM has learned the proper IAC position for desired idle. Vehicle must he driven for IAC to learn.

FUEL TRIM ENABLE - TECH 1 STATES "YES" OR "NO" - "YES" displayed indicates that the L. T. fuel trim is responding to the S. T. fuel trim. The fuel system should begin learning as soon as the system goes into closed loop.

A/C REQUEST - TECH 1 STATES "YES" OR "NO" - Represents the state of the A/C request input from the control head.

A/C CLUTCH - TECH 1 STATES "ON" OR "OFF" - Represents the commanded state of the A/C clutch control relay. Clutch should be engaged when "ON" is displayed.

BRAKE SWITCH - TECH 1 STATES APPLIED OR RELEASED - Represents the state of the TCC brake switch input. Should display "APPLIED" only with the brake pedal depressed.

CRUISE ENGAGED - TECH 1 STATES "YES" OR "NO" - The cruise engaged input informs the ECM whether or not the vehicle is operating in cruise control. When in cruise, the ECM alters TCC operation and spark advance.

POWER STEERING - TECH 1 STATES NORMAL OR HIGH PRESS - Used by the ECM to compensate for the extra engine load caused by power steering cramp.

FAN 1, FAN 2 - TECH 1 STATES "ON" OR "OFF" - Indicates the status of the Cooling Fan ECM outputs. Fan 2 is not used, but it may display "ON" under certain conditions.

QDM A, B - TECH 1 STATES HIGH OR LOW - Indicates the state of the QDM A and B fault lines. Under certain conditions, "HIGH" displayed indicates a fault with a QDM operated circuit or component. QDM B will normally display "HIGH" unless the Fan 2 output is commanded "ON."

TCC - TECH 1 STATES "ON" OR "OFF" - Represents the ECM commanded state of the TCC solenoid; this does not indicate that the TCC is actually applied.

2nd - TECH 1 STATES "YES" OR "NO" - Represents the state of the 2nd gear switch input to the ECM. When the switch opens, "YES" should be displayed.

3rd - TECH 1 STATES "YES" OR "NO" - Represents the state of the 3rd gear switch input to the ECM. When the switch opens, "YES" should be displayed.

4th - TECH 1 STATES "YES" OR "NO" - Represents the state of the 4th gear switch input to the ECM. When the switch opens, "YES" should be displayed.

CALIBRATION ID - TECH 1 RANGE 0-9999 - An internal ECM parameter that can be used to verify that the ECM contains the correct PROM for a particular vehicle application.

TIME FROM START - TECH 1 RANGE 0:00:00-18:12:15 HR/MIN/SEC - A measure of how long the engine has been running. If the engine stops, time from start will reset to 0:00:00.