Scan Tool Data Definitions
POWERTRAIN CONTROL MODULE (PCM) DATA DESCRIPTIONA list of explanations for each data message displayed on the Tech 1 scan tool 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. Refer to the On-Board Diagnostic (OBD) system check for additional information.
ENGINE SPEED - RANGE 0-9999 RPM
Engine speed is computed by the PCM from the fuel control reference input. It should remain close to desired idle under various engine loads with engine idling.
DESIRED IDLE - RANGE 0-3187 RPM
The idle speed that is commanded by the PCM. The PCM will compensate for various engine loads to keep the engine at the desired idle speed.
ENGINE COOLANT TEMP (ECT) - RANGE -40° to 151°C, -40° to 304°F
The Engine Coolant Temperature (ECT) sensor sends engine temperature information to the PCM. The PCM supplies 5 volts to the engine coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the PCM 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 PCM will interpret the lower voltage as a warm engine.
INTAKE AIR TEMP (IAT) - RANGE -40° to 196°C, -40° to 385°F
The PCM converts the resistance of the intake air temperature sensor to degrees. Intake Air Temp (IAT) is used by the PCM 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 in the intake manifold also increases and additional fuel is required.
BARO - RANGE 11-105 kPa / 0.00-5.10 Volts
The Barometric Pressure (BARO) sensor measures the change in the intake manifold pressure which results from altitude changes.
THROTTLE POSITION (TP) - RANGE 0-5.10 Volts
Used by the PCM to determine the amount of throttle demanded by the driver. Should read 0.36 - 0.96 volt at idle to above 4 volts at wide open throttle.
THROTTLE ANGLE - RANGE 0-100%
Computed by the PCM from TP sensor voltage (TP position). Should read 0% at idle, 100% at wide open throttle.
O2S - RANGE 0-996 mV
Represents the exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 100 mV (lean exhaust) and 1000 my (rich exhaust) when operating in "Closed Loop."
INJ PULSE WIDTH - TECH 1 Range 0.0 to 999.9
Indicates the on time of the injectors in milliseconds. When engine load is increased, injector pulse width will increase.
SHORT TERM (ST) FUEL TRIM - RANGE 0-255
Short term fuel trim represents a short-term correction to fuel delivery by the PCM in response to the amount of time the oxygen sensor voltage spends above or below the 450 my threshold. If the oxygen sensor voltage has mainly been below 450 my, indicating a lean air/fuel mixture, short term fuel trim will increase to tell the PCM to add fuel. If the oxygen sensor voltage stays mainly above the threshold, the PCM will reduce fuel delivery to compensate for the indicated rich condition. Under certain conditions such as extended idle and high ambient temperatures, canister purge may cause short term fuel trim to read less than 100 counts.
LONG TERM (LT) 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 PCM is compensating by adding fuel (increased injector pulse width). LONG TERM FUEL TRIM TENDS TO FOLLOW SHORT TERM FUEL TRIM; A VALUE OF LESS THAN 100 COUNTS DUE TO EVAPORATIVE EMISSION CANISTER PURGING AT IDLE SHOULD NOT BE CONSIDERED UNUSUAL.
LOOP STATUS - TECH 1 DISPLAYS "Open" or "Closed"
"Closed Loop" displayed indicates that the PCM is controlling fuel delivery according to oxygen sensor voltage. In "Open Loop," the PCM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on TP sensor, ECT sensor, and MAP sensor inputs only.
FUEL TRIM CELL - RANGE 0-21
Fuel trim cell is dependent upon engine speed and MAP sensor readings. A plot of RPM vs. MAP is broken into 22 cells. Fuel trim cell indicates which cell is currently active.
LO OCT. KNOCK RETARD - RANGE 0° to 45°
Indicates the long term amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
SPARK ADVANCE - TECH 1 Range -90° to 90°
This is a display of the spark advance (IC) calculation which the PCM 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.
KS RETARD - RANGE 0° - 45°
Indicates the amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
KS SIGNAL - TECH 1 DISPLAYS "YES" or "NO"
Indicates whether or not a knock signal is being detected by the PCM. Should read "NO" at idle.
KS ACTIVITY - RANGE 0-255
Indicates if the PCM is receiving the varying frequency output of the knock sensor.
7X RESYNC CNTR. - RANGE 0-255 Counts
DISPLAYS the number of times the PCM had to resync with the Crankshaft Position (CKP) sensor. Helpful with diagnosing DTC 19.
IGN CNTRL 7X REF - RANGE 0-255 Counts
Indicates whether the PCM is receiving 7X pulses from the ignition module, usable to diagnose DTC 19.
IGN CNTRL 7X SYN - RANGE "ON / OFF"
Indicates if the PCM is receiving the 7X sync pulse. This will be helpful in misfire diagnosis.
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 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 DISPLAYS -P-N-- or -R-DL
P-N-- displayed indicates that the gear select lever is in park or neutral. Will always read -R-DL for manual trans vehicles.
MPH km/h - RANGE 0-159 MPH, 0-255 km/h
The vehicle speed sensor signal is coverted into mph and km/h for display.
COOL FAN RELAY - TECH 1 DISPLAYS "ON" or "OFF"
When the PCM is commanding the coolant fan "ON," the Tech 1 display will switch from "OFF" to "ON."
SYSTEM VOLTAGE - RANGE 0.0 to 25.5 Volts
This represents the system voltage measured by the PCM at its ignition feed.
O2S READY - TECH 1 DISPLAYS "YES" or "NO"
Indicates when the engine coolant temperature has reached a specific temperature and the engine has run long enough to allow "Closed Loop" fuel control. Does not mean engine will be in "Closed Loop".
GEN. "F"-TERMINAL - RANGE 0-100%
Monitors generator duty cycle. As generator loads increase, the PCM can adjust idle speed accordingly.
GEN. "L"-TERMINAL - TECH 1 DISPLAYS "Active" or "Inactive."
Indicates whether or not the PCM is allowing the generator to operate. The PCM can disable the generator under certain conditions.
SHIFT LIGHT - TECH 1 DISPLAYS "OFF"or "ON"
The shift light is used to indicated the best point for upshifting. When the shift light "ON," the Tech 1 should display "ON."
ENG OIL PRESS - TECH 1 DISPLAYS "LOW" or "OK."
Indicates if engine oil pressure is "LOW" or "OK."
A/C REQUEST - TECH 1 DISPLAYS "YES" or "NO"
Represents the state of the A/C request input from the control head.
A/C RELAY - TECH 1 DISPLAYS "ON" or "OFF"
Represents the commanded state of the A/C clutch control relay. Clutch should be engaged when "ON" is displayed.
A/C REF PRESS - RANGE 0-450 psi
DISPLAYS the pressure value of the A/C refrigerant pressure sensor, usable to diagnose DTC 66.
QDM A, B, C, D - TECH 1 DISPLAYS "HIGH" or "LOW"
"Output-Driver" modules are used to power various systems. The Tech 1 will display "LOW" and switch to "HIGH" if there is a circuit problem.
FUEL EVAP PURGE - RANGE 0-100%
A proportional signal used to control evaporative emission canister purge function. 0% implies the valve is commanded fully closed while 100% implies that the valve is fully open.
POWER ENRICHMENT - TECH 1 DISPLAYS "OFF" or "ON"
The Tech 1 scan tool only indicates when power enrichment mode is active (moderate to heavy acceleration). Useful for diagnosing DTC 55.
ENG OIL LEVEL - TECH 1 DISPLAYS "LOW" or "OK."
Indicates whether the engine oil level is "LOW" or "OK." This will be helpful in "Oil Level Input" diagnosis.
ENG COOLANT LVL - TECH 1 DISPLAYS "LOW" or "OK"
Indicates if the coolant level is "Low" or "OK."
STEPPER CRUISE - TECH 1 DISPLAYS "ENABLED" or "DISABLED."
Indicates if the PCM is allowing cruise operation. The PCM can disable the cruise under various conditions.
CRUISE ENGAGED - TECH 1 DISPLAYS "YES" or "NO."
Indicates if the cruise control system is in control of vehicle speed. The PCM uses this information to change transmission shift calibrations (automatic electronic trans only) and to turn on an indicator lamp on the instrument cluster (when equipped).
CALIBRATION ID - RANGE 0-999
The EPROM identification describes the particular EPROM being used in the PCM. The Tech 1 display number is not the service part number.
TIME FROM START - RANGE 0:00:00 - 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.