Engine

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. Refer to the "On-Board Diagnostic System Check" for additional information.

ENGINE SPEED - Engine speed is computed by the PCM from the fuel control reference input (low resolution crankshaft position sensor). 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 keep the engine at the desired idle speed.

ENGINE COOLANT TEMP - The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the PCM. The PCM supplies 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 SENSOR - The Intake Air Temperature (IAT) sensor is used by the PCM to adjust fuel delivery and spark timing according to incoming air density. The PCM supplies 5 volts to the IAT thermistor. As intake air temperature varies, the resistance changes causing a change in voltage drop across the sensor. The PCM measures the voltage drop and calculates the air temperature at the air intake.

MAP - The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which results from engine load and RPM changes and converts these into a voltage Output.

BARO - MAP sensor is also used to measure barometric pressure during ignition key "ON" cycle and during Wide Open Throttle (WOT), allowing the PCM to make adjustments for altitudes. The PCM uses the MAP sensor to control fuel delivery and ignition timing.

THROT POSITION - 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 4.0 volts at Wide Open Throttle (WOT).

THROTTLE ANGLE - Computed by the PCM from Throttle Position (TP) sensor voltage (Throttle position); should read 0% at idle, 100% at Wide Open Throttle (WOT)(O2S) output voltage. Should fluctuate constantly within a range between 100 MV (lean exhaust) and 1000 mV (rich exhaust) when operating in "Closed Loop."

O2S LEFT (BANK 2) - Represents the left 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."

SHORT TERM (S.T.) FUEL TRIM - (Bank 1 or Bank2) - This 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, EVAP canister purge may cause short term fuel trim to read less than 100 counts.

LONG TERM (L.T.) FUEL TRIM - (Bank 1 or Bank 2) - 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 O2S signal 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; normal values of 110-150 counts at idle should not be considered unusual.

FUEL TRIM CELL - The 60 degree V6 engine uses sixteen fuel trim cells. Cell sixteen is the idle mode cell. Throttle position and MAP determine which cell the engine will be in.

LOOP STATUS - "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, and MAP sensor inputs only. "Closed Loop" operation should begin when both oxygen sensors become active and engine coolant temperature exceeds 65°C (149°F) for more than 30 seconds.

FUEL TRIM ENABLE - (Tech 1 Will Display "YES") - If fuel trim enable system is learning, the L. T. fuel trim is responding to the S. T. fuel trim. If fuel trim enable reads "NO" then L. T. fuel trim will not respond to changes in S. T. fuel trim.

SPARK ADVANCE - This is a display of the spark advance calculation determined by the Ignition Control (IC) logic which the PCM is delivering to the electronic ignition control module. It computes the desired spark advance using data such as engine coolant temperature, RPM, load, vehicle speed, and operating mode.

SPARK RETARD - Indicates the amount of spark advance the PCM is removing from the Ignition Control (IC) timing in response to the Knock Sensor (KS) signal. Tech 1 should display 0 degrees at idle.

KNOCK SIGNAL - Indicates whether or not a knock signal is being detected by the PCM. Tech 1 should display "NO" at idle.

EGR 1/EGR 2/EGR 3 - Any combination of the EGR solenoids may be opened during engine operation. The Tech 1 can indicate which solenoids are open or when all three are closed, such as at idle. The Tech 1 can cycle each solenoid to evaluate its operation.

IDLE AIR CONTROL - Displays the commanded position of the Idle Air Control (IAC) pintle in counts. The higher the number of counts, the greater the commanded idle speed. Idle Air Control (IAC) should respond fairly quickly to changes in engine load to maintain desired idle RPM.

MPH KM/H - The Vehicle Speed Sensor (VSS) signal is converted into km/h and mph for display.

SYSTEM VOLTAGE - System voltage with ignition "ON" and engine "OFF" will reflect battery voltage. Ignition "ON" engine "ON" will indicate charging system voltage applied to the PCM ignition input.

FUEL PUMP VOLTS - When the ignition switch is turned to the "ON" position, the PCM turns the fuel pump relay "ON" for two seconds. If the PCM does not receive ignition reference pulses within two seconds, the PCM will shut "OFF" the fuel pump.

IGNITION CONTROL 24X SIGNAL - Indicates the PCM is receiving 24X reference signals from the 24X, high resolution crankshaft position sensor.

IGNITION CONTROL CAM SIGNAL - 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 camshaft position sensor.

A/C REQUEST - Represents the state of the A/C request input from the control head.

A/C CLUTCH - Represents the commanded state of the A/C clutch control relay. Clutch should be engaged when "ON" is displayed.

A/C STATUS - The Tech 1 will display "ON" if voltage has been applied to the A/C compressor clutch.

A/C REFRIGERANT PRESSURE - Tech 1 displays refrigerant pressure represented by psi and voltage.

A/C EVAP TEMPERATURE - The Tech 1 will display the A/C system temperature used by the PCM for cooling fan operation, A/C compressor clutch control and A/C diagnostic trouble codes.

ENGINE COOL FAN - When the PCM is commanding the engine cooling fan "ON," the Tech 1 display will switch from "OFF" to "ON." The coolant fan can also he selected as an output test by the Tech 1.

INJECTOR PULSE WIDTH Indicates the on time of the injectors in milliseconds. When engine load is increased, injector pulse width will increase.

FUEL EVAP PURGE - A signal used to control canister purge function. 0% indicates the evaporative emission canister solenoid valve is commanded fully closed while 100% indicates that the valve is commanded fully open.

(TCC) - A/T - The 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 enabled. Refer to Chart C-8.

TCC BRAKE SWITCH - Tech 1 displays "CLOSED" when the brake pedal is at rest and "OPEN" when the brake pedal is applied. The switch sends a signal to the PCM to disengage the TCC.

INJECTOR FAULT - The PCM can determine if any of the six injectors are misfiring. "YES" will be displayed if this is occurring.

CLUTCH PEDAL SWITCH - Tech 1 displays "ON" with the clutch pedal depressed and "OFF" with the clutch pedal at rest.

AIR PUMP RELAY - The Tech 1 displays "ON," when secondary air is commanded by the PCM and "OFF" when conditions do not require secondary air injection.

PASS-Key II - An input from the PASS-Key II decoder module that tells the PCM to enable the injectors if the proper signal is received. The Tech 1 will normally display "OK." If the PASS-Key II test has failed, the display will switch to "FAULT" and the fuel system may be disabled.

DTC IGNITION COUNTER - Tech 1 displays the number of key cycles after a DTC was stored in PCM memory. The count increases by 1 with each key cycle.

DTC STORED - Tech 1 displays the number of history diagnostic trouble codes stored in PCM memory.

TIME FROM START - Range 0:00:00 - 18:12:15 HR/MIN/SEC - A measure of how long the engine has been running. When engine stops, it is reset to zero.