A list of each data message displayed on the scan tool will be explained in Engine Controls. This information will assist in emission or driveability problems. The displays can be viewed while the vehicle is being driven. Always perform the Diagnostic System Check-Engine Controls first. The Diagnostic System Check will confirm proper system operation.

4WD Low Signal-Range Enabled/Disabled: Indicates the current state of the four wheel drive (4WD) low gear.

4WD Signal-Range Enabled/Disabled: Indicates if the 4WD system is Enabled.

A/C Clutch Feedback Signal-Range Relay ON/Relay OFF: Represents the current state of the A/C clutch relay.

A/C Relay Command-Range ON/OFF: Represents the commanded state of the A/C clutch control relay. The A/C clutch should be engaged with ON displayed.

A/C Request Signal-Range Yes/No: Represents the state of the A/C request input from the A/C control head.

A/C Sec. High Press. SW- Range Open/Closed: Represents the current state of the A/C secondary high pressure switch.

APP Indicated Angle-Range 0-100 Percent: Computed by the engine control module (ECM) from accelerator pedal position (APP) module voltage (throttle position) and should display 0 percent at idle and 100 percent at wide open throttle (WOT).

APP 1-3-Range 0-5 Volts: The ECM uses the APP sensors to control fuel delivery as requested by the driver. Three APP sensors are located in a module at the base of the accelerator pedal. The ECM only requires information from one sensor, the other two serve as a fail safe. APP 1 should read about 0.35-0.95 volts at idle to above 4.0 volts at wide open throttle.

Actual Fuel Rail Pressure: Indicates the current fuel rail pressure, as measured by the fuel rail pressure (FRP) sensor.

Alternator L Terminal-Range ON/OFF: Indicates the commanded state of the alternator L terminal.

Balancing Rate Cyl. 1-8: This indicates the adjustment of fuel volume to individual cylinders. The measurement will be negative if fuel volume is lowered, and positive if volume is raised.

BARO-Range 10-105 kPa: The BARO reading is determined from the boost sensor at ignition ON, engine OFF. The BARO reading display represents barometric pressure and is used to compensate for altitude differences.

Battery Voltage-Range 12-14 Volts: This represents the system voltage measured by the ECM at its battery voltage feed circuit.

Boost Pressure Sensor-Range 10-200 kPa: The amount of turbo boost pressure in the intake manifold. True boost pressure is determined by subtracting barometric pressure (BARO) from the actual reading.

Calculated Fuel Rate-Range 0-80 mm³:  This is the amount of fuel the ECM is requesting.

Cam Reference Signal Missed-Range 0- 8: The scan tool will display the number of cam pulses missed. The scan tool should read 0. This number will only increase due to an intermittent condition. If the signal is missing for a longer period, this parameter will remain 0.

Clutch Pedal Switch: This indicates the current state of the clutch pedal switch when vehicle has a manual transmission.

Cruise Control Active-Range Yes/No: Indicates the current state of the cruise control system.

Cruise ON/OFF Switch-Range ON/OFF: Indicates the current state of the cruise ON/OFF switch.

Cruise Resume/Accel Switch-Range ON/OFF: Indicates the current state of the cruise Resume/Accel switch.

Cruise Set Coast Switch-Range ON/OFF: Indicates the current state of the cruise set coast switch.

Desired FRP Regulator: Indicates the desired current draw of the fuel rail pressure regulator. This parameter is used by the ECM in Circuit diagnostics.

Desired Fuel Rail Pressure-Range 37-40 MPa: Indicates the fuel rail pressure desired by the ECM based on current sensor inputs. This can be compared the actual fuel rail pressure to determine sensor accuracy or fuel pressure problems.

Desired Idle Speed-Range 0-3187 RPM: The idle speed that is requested by the ECM. The ECM will compensate for various engine loads based on engine coolant temperature to keep the engine at the desired speed.

DTC Set This Ignition-Range Yes/No: Indicates if a diagnostic trouble code (DTC) has set this ignition cycle.

ECT Sensor-Range -40°C to 151°C, -40°F to 304°F: The engine coolant temperature (ECT) sensor sends a signal to the ECM relative to engine coolant temperature. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage and interprets the high signal voltage as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal will decrease and the ECM will interpret the lower voltage as a warm engine.

Engine Oil Level Switch-Range OK/Fault: Indicates the current status of the engine oil level switch.

Engine Oil Life Remaining-Range 0-100 Percent: Indicates the calculated current oil life remaining according to the ECM. This is based on ECM calculations of mileage, driving conditions, temperature, and load conditions.

Engine Run Time-Range 00:00:00 (HRS/MIN/SEC): A measure of how long the engine has been operating. When the ignition is cycled to OFF the value is reset to zero.

Engine Speed-Range 0-9999 RPM: Engine speed is computed by the ECM from the crankshaft position (CKP) sensor. If the crankshaft position sensor is inoperative, an RPM reading is taken from the injection pump cam signal. The reading should remain close to desired idle under various engine loads with the engine idling. Engine speed value is very accurate.

Front Axle Switch-Range lock/unlock: Indicates the current state of the front axle switch.

FRP Regulator Command-Range 0-100 Percent: Indicates the current commanded duty cycle of the fuel rail pressure regulator.

FRP Regulator Command: Indicates the current (mA) supply to the fuel rail pressure regulator.

FRP Regulator Relay-Range ON/OFF: Indicates the commanded state of the FRP regulator relay.

FRP Regulator Fuel Flow-Range XXX mm³: Indicates the calculated fuel flow through the FRP regulator as determined by the ECM.

Fuel Temperature Sensor-Range -28°C to +140° (-18°F to +285°F): There is a thermistor located in the optical sensor that determines fuel temperature. When the sensor is cold (internal resistance high) the ECM monitors a high signal voltage which it interprets as low fuel temperature. As the sensor warms (internal resistance low) the voltage signal will decrease and the ECM will interpret the low voltage as warm fuel.

Glow Plug Feedback Signal-Range 0-25.5 Volts: The amount of voltage the glow plug system is drawing. The scan tool can be used to indicate if the glow plugs actually turned ON by monitoring the voltage drop. Also, a good functional check of the glow plug relay.

Glow Plug Relay -Range ON/OFF: Glow Plug System-Range ON/OFF Indicates whether or not the ECM has requested the glow plugs to be turned ON.

Glow Plug System Type: Indicates whether the glow plug system is Federal or California. This changes some diagnostic procedures.

IAT Sensor-Range -40°C to +151°C (-40°F to +304°F): The intake air temperature sensor sends a signal to the PCM relative to the incoming air. The intake air temperature (IAT) is used by the ECM to adjust fuel delivery.

Ignition 1 Signal-Range 0-25.5 Volts: This represents the system voltage measured by the ECM at its ignition feed circuit. Ignition voltage is only present when the vehicle is running.

Injector 1-8 Command: Indicates the commanded state of the fuel injectors in milliseconds.

Intake Air Heater Feedback: Indicates the voltage supplied from the intake air heater relay. This can be used to determine if the relay is following the ECM command.

Intake Air Heater Feedback Relay: Indicates the current commanded state of the intake air heater relay.

Intake Air Heater Relay Command: Indicates if the ECM is commanding the intake air heater ON.

Low Coolant Level-Range Yes/No: Indicates if the low coolant switch has been activated.

MAF Sensor: Indicates the amount of air entering the engine through the mass air flow (MAF) sensor.

Main Injection Command-Range XXX Microseconds: Indicates the commanded on time of the fuel injector for the main injection pulse.

Main Injection Fuel Rate: Indicates the commanded amount of fuel in the main injection pulse.

Main Injection Timing-Range XXX °: Indicates the current timing of the main injection pulse.

MIL Command-Range ON/OFF: Represents the commanded state of the service engine soon/malfunction indicator lamp (MIL).

PCM in VTD Fail Enable: The scan tool display is Yes or No. This will indicate that the ECM received a good password from the passlock module and the vehicle has started and a failure has occurred. The ECM will continue to enable fuel.

PCM Reset-Range Yes/No: Indicates if the ECM has been reset this ignition.

Pilot Injection Command: Indicates the commanded on time for the pilot injection pulse.

Pilot Injection Fuel Rate: Indicates the calculated amount of fuel in the pilot injection pulse.

Pilot Injection Timing: Indicates the timing of the small injection of fuel before the main injection pulse.

Reverse Enable-Range Yes/No: Indicates if the vehicle is in reverse.

Start Up ECT- Range -40°C to +151°C (-40°F to +304°F): A reading of the vehicles coolant temperature at startup. This will change every key cycle.

Stop lamp Pedal Switch-Range open/closed: This indicates the current state of the stop lamp pedal switch.

TCC/Cruise Brake Pedal-Range Open/Closed: Indicates the current state of the torque converter clutch (TCC)/cruise brake pedal switch. This is used for stop lamps and a redundant cruise control disengagement switch.

Vehicle Speed Sensor-Range 0-98 mph: Vehicle speed is a ECM 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 and kilometers per hour (km/hr) and miles per hour (mph).

VTD Auto Learn Timer-Range Active/Inactive:  The auto learn timer will indicate if the vehicle theft deterrent (VTD) system is in learn mode and has not timed out (10 minutes.)

VTD Fuel Disable-Range Active/Inactive:  If the ECM has not received the correct password from the passlock module the ECM will disable fuel to the fuel system, and Active will be displayed on the scan tool.

VTD Fuel Disable Until Ign. Off-Range Yes/No:  With the ignition ON and a VTD code stored, the scan tool will display Yes.

Wait to Start-Range ON/OFF: Indicates the commanded state of the Wait to start lamp

Water in Fuel-Range ON/OFF : Indicates the commanded state of the water in fuel lamp.

Freeze Frame and Failure Record Data Definitions: A Freeze Frame/Failure Record data list consist of as many of the same parameters as in an engine data list. The list below defines the parameters not found in an engine data list.

Fail Counter-Range (decimal): The number of ignition cycles that a test has ran and failed (at least once).

First Odometer-Range Miles (x16): The amount of kilometers in 25.75 k increments or miles (16 mile increments) that the vehicle has traveled since the Freeze Frame/Failure Record has been stored.

Last Odometer-Range Miles (x16): Every time a failure occurs, last odometer will reset to zero. This indicates the number of miles since the last failure in 25.75 k increments (16 mile increments).

No Results Counter: The number of ignition cycles without a result (pass or fail).

Pass Counter-Range (Decimal): The number of ignition cycles that a test has run and passed (at least once).