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. See the "On-Board (OBD) Diagnostic 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.
ENG. COOLANT TEMP - Range -40°C to 151°C, -40°F to 304°F - The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine coolant 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 - Range -40°C to 147°C, -40°F to 297°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.
THROTTLE POSITION - Range 0.00-5.00 Volts - Used by the PCM to determine the amount of throttle demanded by the driver. Should read .20- .74 volt at idle to above 4 volts at wide open throttle.
THROTTLE ANGLE - Range 0-100% - Computed by the PCM from TP sensor voltage (Throttle position); should read 0% at idle, 100% at Wide Open Throttle (WOT).
MASS AIR FLOW - Range 0-512 GM/SEC - The PCM converts the mass air flow sensor input signal into grams per second, indicating the amount of airflow entering the engine.
CALC ENG LOAD - Range 0-255- Engine load is calculated by the PCM by engine speed and mass airflow.
Should increase with an increase in RPM or airflow.
HO2S 1 - Range 0-1132 mV - Represents the heated 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."
HO2S 2 - Range 0-1132 mV - Represents the HO2S 2 (catalyst monitor) output voltage. Should fluctuate much more slowly than the HO2S 1 signal when operating in "Closed Loop."
HO2S 1 CROSS COUNTS - Range 0-255- The number of times the oxygen sensor voltage crosses over the rich/lean threshold during a one second interval.
RICH/LEAN STATUS - Tech 1 scanner Displays 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 indicating that the PCM is controlling the air/fuel mixture properly.
VEHICLE SPEED - Range 0-255 km/h, 0-159 MPH - The vehicle speed sensor signal is converted into km/h and mph for display.
SPARK ADVANCE - Range 90° to 90°. This is a display of the spark advance calculation which the PCM is programming into the ignition system. It computes the desi red spark advance using data such as engine temperature, RPM, load, vehicle speed, and operating mode.
INJ PULSE WIDTH - Tech 1 scanner Range 0-999.9 ms - Indicates the length of time the PCM is commanding the injections ON for each injector duty cycle. A longer ON time indicates a rich commanded mixture.
S.T 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 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 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.
L .T. 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 canister purge at idle should not be considered unusual.
LOOP STATUS - Tech 1 scanner Displays "OPEN LOOP" or "CLOSED LOOP" -"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, engine coolant temperature, and MAF sensor inputs only. "Closed Loop" operation should begin when the oxygen sensor becomes active, engine coolant temperature exceeds 50°C (1 22°F) for more than 30 seconds and the PCM has seen a RPM of 1200 or greater for 10 seconds. At extremely high ambient temperatures or when towing a trailer, it is possible for the system to remain in "Open Loop" operation to control catalytic converter temperatures.
FUEL TRIM CELL - Range 0-15 - Fuel trim cell is dependent upon engine speed and 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 - Range 0°-45° - Indicates the amount of spark advance the PCM is removing from ignition control in response to the knock sensor signal. Should read 0° at idle.
KNOCK SIGNAL - Tech 1 Scanner Displays "NO" or "YES" - Indicates whether or not a knock signal is being detected by the PCM. Should read "NO" at idle.
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 Scanner Displays P-N or -R-DL "P-N" displayed indicates that the gear select lever is in park or neutral as indicated by the transmission range switch PRNDL inputs.
TCC BRAKE SWITCH - Tech 1 Scanner Displays "APPLIED" or "RELEASED" - When the brake pedal is applied, the switch sends a signal to the PCM to disengage the TCC and cruise control.
TCC MODE - The modes of operation are OFF RELEASE, APPLY, and ON. The APPLY mode will be active for approximately 1 to 5 seconds.
TCC DUTY CYCLE - Range 0-100% - This is the relative position of the PWM solenoid that controls TCC apply pressure. 100% is low pressure, 0% is full line pressure.
TCC SLIP - Range -255 to +255 RPM - The RPM difference between engine crankshaft speed and torque converter turbine speed. When TCC mode is ON there should only be a small amount of slip.
N/V RATIO - Range 0-255 Counts - Represents the ratio derived by dividing engine RPM by vehicle speed. Should remain steady in 3rd or 4th gear with the TCC applied.
CURRENT WEAK CYL - Tech 1 Scanner Displays Cylinder Number or None - The PCM monitors RPM and crankshaft position and when an apparent misfire is detected for more than 25 consecutive crankshaft revolutions the weak cylinder number is displayed.
EGR PINTLE POSITION - Range 0-5 Volts - Represents the linear EGR pintle position sensor output voltage. Should be under 1 volt at idle.
CAM/CRANK ERROR - Range 0-255 - The Tech 1 scanner displays the number of times an incorrect ratio of cam sensor pulses to fuel control pulses has been detected. A normally operating system may detect 0-2 errors during start up.
TRANS FLUID TEMP - Range -40° to 151°C, -40° to 304°F - The PCM converts the resistance of the transaxle fluid temperature sensor to degrees. Trans fluid temp is used to determine "Hot Mode" TCC operation.
FUEL EVAP PURGE - Range 0-100% - A proportional signal used to control EVAP canister purge function. 0% implies the valve is commanded fully closed while 100% implies that the valve is fully open.
SYSTEM VOLTAGE - Range 0.00-25.5 Volts -This represents the system voltage measured by the PCM at its ignition feed (CKT 439).
A/C REQUEST - Tech 1 scanner Displays "YES" or "NO" - Represents the state of the A/C request input from the control head.
A/C CLUTCH - Tech 1 scanner Displays ON or OFF - Represents the commanded state of the A/C clutch control relay. Clutch should be engaged when ON is displayed.
FAN 1 - When the PCM is commanding the left fan ON, the Tech 1 scanner display will switch from OFF to ON.
FAN 2 - When the PCM is commanding the right fan ON, the Tech 1 scanner display will switch from OFF to ON.
A/C HEAD PRESSURE - Tech 1 scanner Displays OK or HIGH Press - Represents the state of the A/C head pressure switch. When the A/C refrigerant pressure rises above 1448 kPa (210 psi) the switch should open, informing the PCM to turn ON the fan 2 relay.
EGR ACTUAL POS - Range 0-100% - Represents the linear EGR pintle position signal in percent of travel. 0% displayed indicates a closed EGR Valve (EGR flow not allowed).
EGR DESIRED POS - Range 0-100% - The EGR Pintle position which is being commanded by the PCM; should be very close to "ACTUAL EGR POS."
SMCC INHIBITED - Tech 1 scanner Displays "YES" or "NO"- "YES" displayed indicates that the PCM is requesting that cruise control not be allowed to engage. Should display "YES" at idle.
SMCC STATUS - Tech 1 scanner Displays "ENGAGE" or "DISENGAGE" - Represents the SMCC status input from the SMCC II module. Should display "DISENGAGE" unless operating in a cruise control mode.
SHIFT SOL "A"SHIFT SOL "B" - Tech 1 scanner displays ON or OFF - Represents the state of the transaxle shift solenoids. Both should display ON in park or neutral (lst gear commanded).
PRNDL P,A,B,C - Tech 1 scanner Displays "HIGH" or "LOW." A transaxle mounted switch is used as an input to let the PCM know what position the gear select lever is in. Tech 1 scanner status will switch from "HIGH" to "LOW" as different combinations are met. In "PARK," PRNDL P and A will be "LOW"; B and C will be "HIGH."
TRANS. RANGE - The Tech 1 scanner displays the decoded position of the transmission range switch PRNDL inputs. If a valid combination is not seen by the PCM, "D4" will be displayed.
COMMANDED GEAR - The gear that the PCM is commanding the 4T60E transaxle to be in. In "PARK," the Tech 1 scanner will display "First."
PIN - Tech 1 scanner Displays "YES" or "NO" - "YES" displayed indicates that the gear select lever is in park or neutral.
2nd, 3rd, 4th, ACTUAL - Tech 1 scanner Displays "YES" or "NO"
The PCM looks at "PRNDL SWITCH" position and commanded gear. The actual forward gear that the transaxle is in will be the lower of the tw0 because the manual valve can override the PCM commanded gear.
QDM 1, 2, 4 - Tech 1 scanner Displays "HIGH" or "LOW" - Quad-driver modules are used to switch ON various components. The Tech 1 scanner will display "LOW" normally and will switch to "HIGH" if there is a circuit problem.
PASS KEY II FUEL - Tech 1 scanner Displays "ENABLED" or "DISABLED" - Indicates if the PCM is receiving a correct fuel enable signal from the Theft Deterrent System. If "DISABLED" is displayed, the PCM will not allow fuel delivery and the engine will not start.
CALIBRATION I.D. - Range 0-9999 - The calibration identification describes the particular PROM being used in the PCM. The displayed 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.