Scan Tool Data Definitions

A 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 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.

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, - to -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.

THROT POSITION - Range 0-5.10 Volts
Used by the PCM to determine the amount of throttle demanded by the driver. Should read 0.20 - 0.74 volt at idle to above 4 volts at wide open throttle.

THROTTLE ANGLE - Range 0-100%
Computed by the PCM from TP sensor voltage (Throt position); should read 0% at idle, 100% at Wide Open Throttle (WOT).

MASS AIR FLOW - Range 0-255.9 GM / SEC
The PCM converts the mass air flow sensor input signal into grams per second, indicating the amount of airflow entering the engine, in order to calculate the proper amount of fuel to be injected sequentially into the engine cylinders.

CALC ENG LOAD - Range 0-255
Engine load is calculated by the PCM depending on parameter input signals from MAF, TP ECT, IAT sensors. Should increase with an increase in RPM or airflow.

HO2S - Range 0-1132 mV
Represents the 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."

RICH / LEAN STATUS
Tech 1 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.

O2S CROSS COUNTS - Range 0-255
The number of times the oxygen sensor voltage crosses over the rich/lean threshold during a one second interval.

LOOP STATUS - Tech 1 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, ECT sensor, IAT sensor, and MAF sensor inputs only. "Closed Loop" operation should begin when the oxygen sensor becomes active, engine coolant temperature exceeds 50°C (122°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.

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.


INJECTION PULSE WIDTH
Tech 1 Range 0-999.9 mSEC - Indicates the length of time the PCM is commanding the injectors "ON," for each duty cycle. A longer "ON" time indicates a richer commanded mixture.


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 desired spark advance using data such as engine temperature, RPM, load, vehicle speed, and operating mode.


SPARK RETARD - Range O° to 45°
Indicates the amount of spark advance the PCM is removing from ignition control in response to the knock sensor signal. Should read 0 degrees at idle.


KNOCK SIGNAL
Tech 1 Displays "NO" or "YES" - Indicates whether or not a knock signal is being detected by the knock sensor. Should read "NO" at idle. PCM uses signal from KS to retard ignition timing.

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.


IGNITION CONTROL CAM SIGNAL
Provides the PCM with information when #1 cylinder intake valve is opening. Based on this signal and depending on the cylinder firing order, the PCM will synchronize Sequential Fuel Injection with each intake valve opening.


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.


POWER STEERING
Tech 1 States Normal or High Pressure - PCM compensates engine idle depending on steering load conditions. Tech 1 will display high pressure due to increase of power steering fluid pressure, while turning steering wheel. Tech 1 displays "normal" under no load condition.

EGR 1, 2, 3
Tech 1 Displays "OFF" or "ON" - Represents the PCM commanded state of the EGR valve solenoids.

CURRENT WEAK CYL
Tech 1 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.

A/C REQUEST
Tech 1 Displays "NO" or "YES" - Represents the state of the A/C request input from the control head.

A/C CLUTCH
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 REFRIGERANT PRESSURE
Tech 1 Displays psi - A/C refrigerant high pressure side sensor sends input signals to the PCM to indicate to the PCM how much load the A/C compressor puts on the engine. The A/C refrigerant pressure sensor has an operation range from 0 psi to 459 psi.

FAN 1
When the PCM is commanding the puller fan or low speed fans "ON," the Tech 1 display will switch from "OFF" to "ON."

FAN 2
When the PCM is commanding the pusher fan or high speed fans "ON," the Tech 1 display will switch from "OFF" to "ON."

PRNDL P,A,B,C
Tech 1 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 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 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.

TCC BRAKE SWITCH
Tech 1 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.

COMMANDED GEAR
The gear that the PCM is commanding the 4T60E transaxle to be in. In "PARK," the Tech 1 will display "First."

VEHICLE SPEED - Range 0-255 km/h, 0-159 MPH
The vehicle speed sensor signal is converted into km/h and mph for display.

TCC APPLY SOL.
The modes of operation are "OFF," "RELEASE," "APPLY," and "ON." The "APPLY" mode will be active for approximately 1 to 5 seconds.

TCC PWM Sol. - 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 that results in TCC engagement.

TCC SLIP SPEED - Range -256 to +254 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.

TRANS FLUID TEMP - Range -40°C to 151°C, -40°F to 304°F
The PCM converts the resistance of the transaxle temperature sensor to degrees. Trans temp is used to determine "Hot Mode" TCC operation.

2nd GEAR START SWITCH
Tech 1 displays "OFF" or "ON" - The 4T60E transaxle is equipped with a 2nd Gear Start Switch that will turn "ON" shift solenoid "B" and turn "OFF" shift solenoid "A" when switch is selected "ON." Vehicle will start motion in second gear for better traction, following gears will shift as normal. Wide Open Throttle (WOT) will override the 2nd Gear Select Switch, vehicle will take off in 1st gear.

SMCC STATUS
Tech 1 Displays "OFF" or "ON" - Represents the SMCC status input from the SMCC II module. Should display "OFF" unless operating in a cruise control mode.

QDM A, B
Tech 1 Displays "HIGH" or "LOW" - Quad-driver modules are used to switch "ON" various components. The Tech 1 will display "LOW" normally and will switch to "HIGH" if there is a circuit problem.

PASS-Key II FUEL
Tech 1 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.

SYSTEM VOLTAGE - Range 0-25.5 Volts
This represents the system voltage measured by the PCM at its ignition feed, CKT 439 at PCM connector "B5."

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.