Scan Tool Data Definitions

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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.
Actual Fuel Rail Pressure-MPa/PSI: Indicates the current fuel rail pressure, as measured by the fuel rail pressure (FRP) sensor.
APP Indicated Angle-Range 0-100 Percent: Computed by the engine control module (ECM) from accelerator pedal position (APP) module voltage, throttle position TP, and should display 0 percent at idle and 100 percent at wide open throttle (WOT).
APP Sensor 1: This parameter displays the voltage signal sent to the control module from accelerator pedal position (APP) sensor 1 of the APP sensor assembly. APP sensor 1 is a range of values indicating a low voltage when the accelerator pedal is not depressed to a high voltage when the accelerator pedal is fully depressed.
APP Sensor 2: This parameter displays the voltage signal sent to the control module from accelerator pedal position (APP) sensor 2 of the APP sensor assembly. APP sensor 2 is a range of values indicating a high voltage when the accelerator pedal is not depressed to a low voltage when the accelerator pedal is fully depressed.
APP Sensor 3: This parameter displays the voltage signal sent to the control module from accelerator pedal position (APP) sensor 3 of the APP sensor assembly. APP sensor 3 is a range of values indicating a high voltage when the accelerator pedal is not depressed to a low voltage when the accelerator pedal is fully depressed.
Auxiliary Gen L-Terminal: Indicates the commanded state of the GEN L terminal on the auxiliary alternator.
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 barometric pressure (BARO) reading is determined from the boost sensor at ignition ON, engine OFF. The BARO reading display is used to compensate for altitude differences.
Battery Voltage-Range 12-14 Volts: This represents the system voltage measured by the ECM at the ECM 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 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.
Check Trans Lamp: Represents the commanded state of the check transmission lamp.
CKP Sensor Pulses Missed-Range 0- 8: The scan tool will display the number of crankshaft position (CKP) 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 (ECT) 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 to 151° C, -40 to 304° F: The 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.
EGR Vacuum Sensor: Indicates the pressure in the exhaust gas recirculation (EGR) vacuum control system.
EGR Solenoid Command: Represents the commanded state of the EGR solenoid.
EGR Throttle Valve Solenoid Command: Indicates the commanded state of the EGR throttle valve solenoid of the EGR system.
EGR vent solenoid Command: Represents the commanded state of the EGR vent solenoid.
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 CKP sensor. If the CKP 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.
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: Indicates the calculated fuel flow through the FRP regulator as determined by the ECM.
Front Axle Switch-Range lock/unlock: Indicates the current state of the front axle switch.
Fuel level sensor: Indicates the current fuel level percentage in the fuel tanks.
Fuel Temperature Sensor-Range -28 to +140° C (-18 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.
GEN L Terminal-Range ON/OFF: Indicates the commanded state of the GEN L terminal.
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.
High Idle Switch: This parameter displays the state of the high idle request input to the control module from the High Idle Switch. The scan tool will display ON or OFF. ON indicates the control module is receiving a request from the high idle switch to increase engine speed. OFF indicates the control module is not receiving a request from the high idle switch to increase engine speed.
IAT Sensor-Range -40 to +151° C (-40 to +304° F): The intake air temperature (IAT) sensor sends a signal to the PCM relative to the incoming air. The 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 (ms).
Intake Air Heater Feedback Signal: 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: 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: 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: 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.
PNP Switch: Indicates the current state of the PNP switch.
PTO Enable: This parameter indicates all parameter have been met to enable the PTO, and the control module has determined that the PTO is engaged.
PTO Engage Relay Command: This parameter displays the commanded state of the PTO relay control circuit. The scan tool will display ON or OFF. ON indicates the PTO relay control circuit is being grounded by the control module, allowing voltage to the load engage switch. OFF indicates the PTO relay is not being commanded on by the control module.
PTO Engine Shutdown Signal: This parameter displays the input status of the PTO engine shutdown switch to the control module. The scan tool will display YES or NO. Yes indicates the PTO engine shutdown switch is closed, grounding the engine shutoff signal circuit to the control module. OFF indicates the engine shutoff switch is open, allowing normal engine and PTO operation.
PTO Feedback Signal: This parameter displays the state of the Power take-off (PTO) based on the signal from the switched side of the PTO relay. The scan tool will display Relay On or Relay Off. Relay On indicates the PTO relay has closed, allowing voltage to the load engage switch. Relay Off indicates the PTO relay is open and the PTO will not engage.
Reverse Enable-Range Yes/No: Indicates if the vehicle is in reverse.
Start Up ECT- Range -40 to +151° C (-40 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 switch-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/h) 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.