Engine Data Definitions
ENGINE TECH 1 DATA DEFINITIONSA list of "Engine" data messages displayed on the Tech 1 scan tool will be explained. This information will assist in emission or driveability problems. The displays can be viewed while the vehicle is being driven. Always perform the On-Board Diagnostic System Check first. This will confirm proper system operation.
With the Tech 1 connected, the Traction Control System (TCS) may be disabled and the "Service TCS" lamp may turn "ON."
Engine Speed
Range 0-9999 RPM Engine speed is computed by the Powertrain Control Module (PCM) from the distributor reference input (low resolution circuit). 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 based on engine coolant temperature to keep the engine at the desired speed.
Eng Cool Temp
Range -40°C to 151°C, -40°F to 304°F - The Engine Coolant Temperature (ECT) sensor is mounted in the coolant pump 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 and interprets it 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 151°C, -40°F to 304°F - The PCM converts the resistance of the intake air temperature sensor to degrees. Intake Air Temperature (IAT) is used by the PCM to adjust fuel delivery and spark timing according to incoming air density.
MAP
Range 10-105 kPa/0.00-5.00 Volts - The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure from engine load and speed changes. As intake manifold pressure increases, the air density in the intake manifold also increases.
BARO
Range 10-105 kPa/10.00-5.00 Volts - The BARO reading displayed is determined from the MAP sensor at ignition "ON," engine "OFF," and WOT conditions. The BARO reading displayed represents barometric pressure and is used to compensate for altitude differences.
Throt Position
Range 0-5.00 Volts - Used by the PCM to determine the amount of throttle demanded by the driver. The display should read 0.36-0.96 volt at idle to greater than 4 volts at wide open throttle
Throttle Angle
Range 0 - 100% - Computed by the PCM from TP sensor voltage (throttle position) and should display 0% at idle and 100% at wide open throttle. Refer to DTC 21 if TP sensor angle is not 0% at idle.
Heated Oxygen Sensors (Bank 1 and 2)
Range 0-1132 mV - Represents the exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 10 mV (lean exhaust) and 1000 mV (rich exhaust) when operating in "Closed Loop."
Loop Status
Tech 1 Displays OPEN or CLOSED - "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 Throttle Position (TP) sensor, engine coolant, and MAP sensor inputs only.
Short Term Fuel Trim
Range 0-255 Counts - 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 remained less than 450 mV, indicating a lean air/fuel mixture, short term fuel trim will increase and the PCM will 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.
Long Term Fuel Trim
Range 0-255 Counts - 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 less than 128 counts indicates that the fuel system is rich and fuel delivery is being reduced (decreased injector pulse width). A value greater than 128 counts indicates that a lean condition exists and the PCM is compensating by adding fuel (increased injector pulse width).
Fuel Trim Cell
Range 0-255 - Fuel trim cell is dependent upon engine speed and MAP sensor readings. A plot of RPM vs. MAP is broken into 16 cells. Fuel trim cell indicates which cell is currently active.
Fuel Trim Enable
Tech 1 displays NO/YES - If the fuel trim enable system indicates "YES," the long term fuel trim is responding to the short term fuel trim. If the Fuel Trim Enable indicates "NO," then long term fuel trim will not respond to changes in short term fuel trim.
Spark Advance
Tech 1 range 0°-255° - This is a display of the spark advance Ignition Control (IC) calculation which the PCM calculates and then provides all spark advance to the ignition system. The PCM computes the desired spark advance using data such as engine coolant temperature, RPM, load, vehicle speed, and operating mode. There is no adjustment for spark advance.
Mass Air Flow
Tech 1 range 0-512 - Displays grams per second. The PCM converts the mass air flow sensor input signal into grams per second, indicating the amount of air flow entering the engine.
Knock Retard
Range 0° to 128° - Indicates the amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
Knock Signal
Tech 1 displays YES/NO - Indicates whether or not a knock signal is being detected by the PCM. Should display "NO" at idle,
LO Resolution Signal
Range 0-1000 m/sec - This signal is generated by the ignition control module and should display time between low resolution signal reference pulses detected by the PCM.
HI Resolution Signal
Tech 1 displays YES/NO - This signal is generated by the ignition control module and will switch from "NO" to "YES" when the PCM detects a high resolution signal.
Injector Pulse Width
Tech 1 range 0.0-1000 m/sec - Indicates the time the injectors remain "ON." When engine load is increased, injector pulse width will increase.
Idle Air Control
Range 0-255 - Displays the commanded position of the idle air control pintle in counts. The greater the number of counts, the greater the idle air passages opened. Idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM.
Learned IAC
Range 0-255 counts - Learned Idle Air Control (IAC) is an internal PCM parameter. Each time the vehicle is driven the IAC system learns how many counts is required to produce a given desired idle.
EGR Duty Cycle
Range 0-100% - The PCM cycles the Exhaust Gas Recirculation (EGR) solenoid valve "ON" and "OFF." The "ON" time (duty cycle) of the EGR solenoid valve, expressed as a percent, determines how much the exhaust gas is recirculated.
System Voltage
Range 0.0-25.5 Volts - This represents the system voltage measured by the PCM.
Air Control
Tech 1 displays ON/OFF - When the PCM enables the secondary air injection system, the Tech 1 will display Air Control "ON." When the PCM determines that AIR Control is not required the Tech 1 will display "OFF."
Fuel EVAP Purge
Tech 1 range 0-100% - Used to control Evaporative Emissions System (EVAP) canister purge function. 0% indicates the valve is commanded fully closed while 100% indicates that the valve is fully open.
Injector Fault
Tech 1 displays YES/NO - "YES" indicates that the PCM does not detect voltage at the injector driver. After the ignition has been "OFF" for 10 seconds, turn ignition to the "ON" position. Injector faults should indicate "NO."
TCS/ASR
Tech 1 displays YES/NO - When the Traction Control System (TCS) TCS/Acceleration Slip Regulation (ASR) system is active, the Tech 1 will display "YES."
FAN 1, FAN 2
Tech 1 displays OFF/ON - When the PCM commands a coolant fan "ON," the Tech 1 display will display "ON."
A/C Request
Tech 1 displays YES/NO - Represents if the A/C request from the control head is being received by the PCM.
A/C Clutch
Tech 1 displays ON/OFF - Represents the command state of the A/C clutch control relay. Clutch should be engaged when "ON" is displayed.
A/C Status
Tech 1 displays ON/OFF - The Tech 1 will display "ON" if voltage has been applied to the A/C compressor clutch.
A/C Refrig Pressure
Range 0-459 psi / 0.00-5.0 Volts - The Tech 1 will display the A/C refrigerant pressure used by the PCM for cooling fan operation and A/C diagnostic trouble codes.
TCC Fluid Temp Switch
Tech 1 Displays Open/Closed - This parameter indicates the state of the [1][2]Torque Converter Clutch (TCC) fluid temp switch circuit input. At 164°C (327°F), the switch will close and the input to the PCM drops to 0 volts. When the switch is open the input voltage will be B+.
Vehicle Speed
Range 0-255 km/h, mph - The vehicle speed sensor signal is converted into km/h and mph for display.
Power Steering Pressure (PSP) Switch
Tech 1 displays Open/Closed. Switch closes when power steering load is present. Signals PCM to increase idle speed during parking maneuvers etc.
Trans Range Switch (SW)
Scan tool displays a range of Invalid, Park/Neutral, Reverse, Drive 4, Drive 3, Drive 2, and Low This parameter is the decoded status of the three A/B/C Range inputs from the Transmission Range Pressure Switch Assembly and represents the position of the transmission manual valve.
Park/Neutral POS
Tech 1 displays P-N-- or -R-DL - P-N-- displayed indicates that the gear select lever is in park or neutral.
TCC Brake Switch
Scan Tool displays OPEN/CLOSED - This parameter indicates the state of the TCC brake switch circuit input. Open indicates a 0 voltage input (brake switch open, brake pedal applied). Closed indicates a B+ voltage input (brake switch closed, brake pedal released).
TCC Solenoid
Displays NO/YES - The Tech 1 only indicates when PCM has enabled the 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.
TCC PWM Solenoid
Displays ON/OFF - This parameter is the commanded state of the TCC PWM solenoid. "ON" indicates a commanded energized state (current flowing through the solenoid). "OFF" indicates a commanded non-energized state (current not flowing through the solenoid).
1 - 2 Shift Sol
Tech 1 displays ON/OFF - When the transmission in in first or fourth gear, the Tech 1 should display "ON." When the transmission is in second or third gear, the Tech 1 should indicate "OFF."
2 - 3 Shift Sol
Tech 1 displays ON/OFF - When the automatic transmission is in first or second gear, the Tech 1 should indicate "ON." When the transmission is in third or fourth gear, the Tech 1 should display "OFF."
Eng Or Trans DTC Detected
Tech 1 displays YES/NO - This will display "YES" if the PCM detects a fault in an engine or transmission circuit that caused a Diagnostic Trouble Code (DTC).
Knock Sensors
Tech 1 displays 0K/One Open/Both Open/Grounded - The PCM monitors the KS circuit and can determine if one or both sensors are open, if both sensors are grounded, or if the circuit is "OK."
Time From Start
Range 0:00:00-18:12:15 HR/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.