Scan Tool Data Definitions
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 On-Board Diagnostic (OBD) System Check for additional information. Testing and Inspection
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 - Range -40°C to 151°C, -40°F to 304°F - The Engine Coolant Temperature (ECT) sensor is mounted in the coolant stream and sends engine temperature information to the PCM. The PCM 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 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.
INT AIR TEMP - Range -38°C to 199°C, -36°F to 390°F - The PCM converts the resistance of the Intake Air Temperature (IAT) sensor to degrees. Intake air temperature 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, varying the signal voltage. The MAP sensor is also used to measure barometric pressure at start up and other certain conditions, which allows the PCM to automatically adjust for different altitudes.
BARO - Range 11 - 105 kPa / 0.00 - 5.10 volts - This parameter represents a measurement of barometric air pressure and is used in conjunction with manifold air pressure to determine manifold vacuum. Since barometric air pressure depends on altitude, it may vary from 100 kPa (sea level) to 60kPa (14,000 ft.).
TP SENSOR - Range 0-5.10 Volts - Used by the PCM to determine the amount of throttle demanded by the accelerator. Should read 0.33 - 1.33 volt at idle to above 4 volts at wide open throttle.
TP ANGLE - Range 0-100% - Computed by the PCM from Throttle Position (TP) sensor voltage. Throttle Angle should read 0% at idle, 100% at Wide Open Throttle (WOT).
OXYGEN SENSOR - Range 0-1132 mV - Represents the exhaust Oxygen Sensor (O2S) output voltage. Should fluctuate constantly within a range between 100 mV (lean exhaust) and 1000 mV (rich exhaust) when operating in "Closed Loop."
INJECTOR PULSE WIDTH Range 0-999 mS - Indicates the "ON" time of the fuel injector(s) in milliseconds. When engine load is increased, injector pulse width will increase.
SPARK ADVANCE - Range -90° to 90° - This is a display of the spark advance Ignition Control (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.
LO OCT RET - 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.
SHORT TERM (ST) FUEL TRIM - Range 0-255- ST 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 mV threshold. If the oxygen sensor voltage has mainly been below 450 mV, indicating a lean air/fuel mixture. fuel integrator 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 ST fuel trim to read less than 100 counts.
LONG TERM (LT) FUEL TRIM - Range 0-255. LT fuel trim is derived from the ST 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). LT FUEL TRIM tends to follow ST FUEL TRIM; a value of less than 100 counts, due to canister purge at idle, should not be considered unusual.
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-D-L" - "P-N" displayed indicates that the gear select lever is in park or neutral.
FUEL TRIM CELL - Range 0-21 - Fuel trim cell is dependent upon engine speed and manifold absolute pressure readings. A plot of RPM vs. MAP is broken into 21 cells. Fuel trim cell indicates which cell is currently active.
FUEL TRIM ENABLE - Tech 1 Displays "NO" or "YES" - If the fuel trim system is learning "YES," it is responding to the Short Term (ST) fuel trim. If fuel trim enable is displayed as "NO," then it will not respond to changes in the ST fuel trim.
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 Throttle Position (TP), Engine Coolant Temperature (ECT), and MAP sensor inputs.
KNOCK RETARD - Range 0°-90° - Indicates the amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
KNOCK 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 COUNTER - 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.
IGNITION CONTROL 7X REF - Range 0-255 Counts - Indicates whether the PCM is receiving 7X pulses from the CKP Sensor, usable to diagnose DTC 19.
IGNITION CONTROL 7X SYNC - Range "YES/NO" - Indicates if the PCM is receiving the 7X sync pulse. This will be helpful in misfire diagnosis.
EGR SOLENOID - Tech 1 Displays "OFF" or "ON" - The EGR valve should be open when the Tech 1 displays "ON" with engine RPM about 2000.
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.
QDM 1, 2, 3 - Tech 1 Displays "HIGH" or "LOW" - "Quad-Driver" modules are used to power various systems. The Tech 1 will display "LOW" and switch to "HIGH" if there is a circuit problem. QDMB WILL NORMALLY SWITCH TO "HIGH" WITH NO CIRCUIT PROBLEM WITH THE BRAKE APPLIED.
VEHICLE SPEED - Range 0-255 mph, 0-255 kph - The vehicle speed sensor signal is converted into kph and mph for display.
(TCC)/SHIFT LIGHT - Tech 1 Displays "OFF" or "ON" - A/T - Tech 1 only indicates when the PCM has enabled the 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 enable.
M/T - The shift light is used to indicate the best point for upshifting. When the shift light is "ON," the Tech 1 should display "ON."
FAN RELAY - Tech 1 Displays "OFF" or "ON" - Tech 1 indicates status of the engine cooling Fan Control (FC) relay. The cooling fan control relay should turn "ON" when coolant temperature reaches 106°C (223°F) then "OFF" when engine coolant temperature then falls below 99°C (210°F). The cooling fan control relay will also be turned "ON" if a DTC 14 is set or when A/C or DEF is selected and A/C head pressure reaches 51 psi. The cooling fan control relay will also be turned "OFF" if A/C head pressure falls to 41 psi with A/C or DEF selected and engine coolant temperature below 99°C (210°F).
A/C REQUEST - Tech 1 Displays "NO" or "YES" - This signal indicates to the PCM that air conditioning mode is selected by the switch. The PCM will then look for correct refrigerant pressure from the A/C pressure sensor input. The PCM uses this signal to adjust the idle speed before turning the A/C compressor clutch "ON" or "OFF."
A/C RELAY - Tech 1 Displays "OFF" or "ON" - Represents the commanded state of the A/C compressor clutch control relay. Clutch should be engaged when "ON" is displayed.
A/C REF. PRESSURE - Range O-459 psi / 0-4.9 Volts - The Air Conditioning (A/C) pressure sensor provides a signal to the PCM which indicates varying high side refrigerant pressure between about 0 psi and 450 psi. The PCM uses this input to determine A/C compressor load on the engine to help control idle speed with the Idle Air Control (IAC) valve.
SYSTEM VOLTAGE - Range 0.0 to 25.5 Volts - Tech 1 indicates the battery voltage detected at the PCM ignition input.
CALIBRATION ID - Range 0-9999 - The calibration identification describes the particular calibration 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.