Scan Tool Data Definitions
POWERTRAIN CONTROL MODULE (PCM) DATA DESCRIPTIONSA 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 driveablity problems, since the displays can be viewed while the vehicle is being driven. Refer to the Typical Scan Data Values. Under Scan Tool Diagnostics Scan Tool Data List
ENGINE SPEED
Engine speed is computed by the PCM from the low resolution 3X Crankshaft Position Sensor (CPS) . It should remain close to desired idle under various engine loads with engine idling.
DESIRED IDLE
The calculated idle speed that is commanded by the PCM. The PCM will compensate for various engine loads to maintain the engine at the desired idle speed.
ENGINE COOLANT TEMP (ECT)
The ECT sensor is mounted in the intake manifold and sends engine coolant temperature information to the PCM. The sensor is a thermistor which changes internal resistance as coolant 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 (IAT)
The PCM converts the resistance of the intake air temperature sensor to degrees. IAT is used by the PCM to adjust fuel delivery and spark timing according to incoming air temperature.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor measures the change in the intake manifold pressure from engine load and RPM changes and converts these into a voltage output. The voltage is also converted to kilopascals (kPa) units.
BAROMETRIC PRESSURE (BARO)
The BARO reading displayed is determined from the MAP sensor at ignition "ON," engine "OFF," and Wide Open Throttle (WOT) conditions,allowing the PCM to make fuel adjustments for altitudes. The PCM uses the MAP sensor to control fuel delivery and Ignition timing.
THROT POSITION (TP)
Used by the PCM to determine the amount of throttle demanded by the driver. Should read 0.29-0.98 volt at idle to above 4 volts at WOT.
THROTTLE ANGLE
Computed by the PCM from TP sensor voltage (throttle position) and should display 0% at idle and 100% at WOT.
PARK/NEUTRAL POSITION (P/N)
P/N displayed indicates that the gear select lever is in "Park" or Neutral."
HEATED OXYGEN SENSOR (HO2S)
The HO2S has an internal heater element to decrease warm up time and maintain operating temperature at idle. This represents the amount of O2 in the exhaust. Should fluctuate constantly within a range between 40mV (lean exhaust or high O2 content) and 800 mV (rich exhaust or low O2 content)when operating in "Closed Loop."
INJECTOR PULSE WIDTH
This represents the duration that the injectors are turned on each time they are enabled. Time units are scaled in thousandths of seconds or milliseconds.
SHORT TERM FUEL TRIM
Fuel integrator represents a short term correction to fuel delivery by the PCM in response to the amount of time the HO2S voltage spends above or below the 450 mV threshold. If the HO2S 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 HO2S voltage stays mainly above the threshold, the PCM will reduce fuel delivery to compensate for the indicated rich condition.
NOTE: Undercertain conditions such as high ambient temperatures, EVAP canister purge may cause short term fuel trim to read less than 100 counts.
LONG TERM FUEL TRIM (BLOCK LEARN)
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 HO2S signal condition exists and the PCM is compensating by adding fuel (increased injector pulse width).
NOTE: Long term fuel trim tends to follow short term fuel trim; normal values of 110-135 counts at idle should not be considered unusual.
FUEL TRIM CELL
The 60^ V6 engine uses sixteen fuel trim cells. Cell sixteen is the idle cell. RPM and MAP determine which cell the engine will use.
LOOP STATUS
"Closed Loop" displayed indicates that the PCM is controlling fuel delivery according to HO2S sensor voltage. In "Open Loop," the PCM ignores the HO2S voltage and bases the amount of fuel to be delivered to TP sensor, RPM, engine coolant, and MAP sensor inputs. "Closed Loop " is determined by HO2S activity, a timer in seconds based on start-up coolant temperature and engine coolant temperature.
FUEL TRIM ENABLE
If air fuel system is learning (YES) then long term fuel trim is responding to short term fuel trim. If fuel trim enable reads (NO) then long term fuel trim will not respond to change in short term fuel trim.
SPARK ADVANCE
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.
KNOCK SIGNAL
Tech 1 scan tool Displays "YES" or "NO" - Indicates whether or not a knock signal is being detected by the PCM.
SPARK RETARD -
Indicates the amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
FUEL EVAP PURGE
Used to control EVAP canister purge function. 0% indicates the valve is commanded fully closed while 100% indicates that the valve is fully open.
EGR1/EGR2/EGR3
Any combination of the three Exhaust GAS REGULATOR (EGR) solenoids may be open during engine operation. The Tech 1 scanner can indicate which solenoids are commanded open or when all three are closed, such as at idle. The Tech 1 scanner can also cycle each solenoid open and closed to evaluate their operation.
IGNITION CONTROL 24X SIGNAL
This signal is represented in RPM and indicates the 24X CPS is operating and PCM is receiving its signal.
IGNITION CONTROL CAM SIGNAL (CAM)
The ignition control CAM signal provides the PCM with the information to determine when the intake valve on number one cylinder will open. "0" CLOSED, "1" OPENED. The PCM sequences the injectors in cylinder firing order based on the input from the camshaft sensor.
MPH/km/h
Vehicle speed is a PCM internal parameter. It is computed by timing pulses coming from the Vehicle Speed Sensor (VSS). Vehicle speed is used in checking TCC lock-up speed or speedometer accuracy. Speed is displayed in both Miles Per Hour (mph) and Kilometer Per Hour (km/h).
TCC APPLY SOLENOID
Tech 1 Scanner displays TCC "OFF" or "ON" as commanded by the PCM.
SYSTEM VOLTAGE
This represents the system voltage measured by the PCM.
IDLE AIR CONTROL (IAC)
Displays the commanded position of the IAC pintle in counts. The greater the number of counts. IAC valve should respond fairly quickly to changes in engine load to maintain desired idle RPM.
A/C REQUEST
Represents the state of the A/C request input from the control head.
A/C CLUTCH
Displays "ON" when the PCM has commanded the A/C clutch "ON".
A/C REFRIGERANT PRESSURE
Tech 1 scanner displays high side refrigerant pressure represented by psi and voltage.
FUEL PUMP VOLTS
This parameter is a reading of the voltage going to the fuel pump motor. This voltage is sensed from a splice located between the fuel pump relay and the pump motor. This voltage should indicate system voltage when the ignition key is cycled "ON" for 2 seconds, or whenever the 3X crankshaft position sensor is supplying reference pulses.
FAN 1
When the PCM is commanding FAN 1 "ON," the Tech 1 scanner display will switch from "OFF" to "ON."
FAN 2 (IF APPLICABLE)
When the PCM is commanding FAN 2 "ON," the Tech 1 scanner will switch form "OFF" to "ON."
INJECTOR FAULT
The PCM can determine if any of the six injectors are misfiring. "FAULT" will be displayed if this is occurring.
SMCC ENGAGED (IF APPLICABLE)
The PCM monitors the "Cruise Status" circuit and determines whether the Stepper Motor Cruise Control (SMCC) module is actually energized, "YES" or not engaged "NO."
LOW OIL LIGHT (IF APPLICABLE)
The PCM monitors the signal from the oil level sensor and turns this telltale "ON" if oil level is below the desirable level. The lamp is energized for about one second after "Key ON" (bulb check) the lamp turns "OFF" as long as PCM is satisfied that the oil level is sufficient.
HOT ENGINE LIGHT (IF APPLICABLE)
Some vehicles are equipped with a "Temp" symbol telltale. This warns the driver of an engine overheating condition. Other vehicles are equipped with a "Check Gauges" lamp which can warn the of several other conditions including low fuel level, generator output, engine overheating, etc. The Tech 1 scanner can energize the "Check Gauges" or "Temp" telltale depending on the particular application, as long as it is a PCM controlled lamp.
SHIFT SOLENOID "A" (SSA)
The PCM monitors the TP sensor and VSS vs RPM to determine the correct shift points. 1st gear "ON", 2nd gear "OFF," 3rd gear "OFF," and 4th gear 'OFF.
SHIFT SOLENOID "B" (SSB)
The PCM monitors the TP sensor and VSS vs RPM to determine the correct shift points. 1st gear "ON", 2nd gear "ON," 3rd gear "OFF," and 4th gear 'OFF.
PRNDL
The Tech 1 scanner can determine through 4 inputs from the transaxle range switch what position the gearshift lever is in. These inputs are A, B, C and a parity input.
TRANS RANGE SWITCH
The Tech 1 scanner displays the decoded position of the trans range switch PRNDL inputs. If an error combination is seen by the PCM, "INVALID" or an incorrect gear range will be displayed.
2nd GEAR START SWITCH
Some 4T60E transaxle are equipped with a 2nd gear start switch. When this switch displays "ON," shift solenoid "A" is "OFF" while shift solenoid "B" is "ON." This gives the vehicle the ability to start out in second gear.
TRANS FLUID TEMP
This signal is received from a 2 wire sensor located in the transaxle fluid stream. The PCM uses this input to determine shift points and TCC engagement points.
TCC BRAKE SWITCH
Tech 1 Scanner displays from "Released" to "Applied" when the brake pedal is applied. The switch sends a signal to the PCM to disengage the TCC.
TCC SLIP SPEED
The RPM difference between engine crankshaft speed and torque converter output speed. When TCC mode is "ON," there should be a small amount of slip.
DIAGNOSTIC TROUBLE CODE (DTC) IGNITION COUNTER
Tech 1 scanner displays the number of key cycles after a DTC was stored in PCM memory. The count increases by 1 with each cycle.
DTC STORED
Tech 1 scanner displays the number of history DTCs stored in memory.
CALIBRATION ID
The calibration identification describes the particular program being used in the PCM. The Tech 1 scanner display number is not the service part number.
TIME FROM START
A measure of how long the engine has been running. When the engine stops, it is reset to zero.