Scan Tool Data Definitions
ECM DATA DESCRIPTIONA 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 (OBD) system check for additional information. With the Tech 1 connected, the ASR system may be disabled and the "Service ASR" light may turn "ON."
ENGINE SPEED - Range 0-9999 RPM
Engine speed is computed by the ECM from the ignition control module reference input. 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 ECM. The ECM will compensate for various engine loads to keep the engine at the desired speed.
ENGINE COOLANT TEMP - Range -40°C to 151°C, -40°F to 304°F
The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM supplies 5 volts to the Engine Coolant Temperature (ECT) sensor circuit. 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 which interprets it 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.
INT AIR TEMP - Range -40°C to 196°C, -40°F to 385°F
The ECM converts the resistance of the intake air temperature sensor to degrees. Intake Air Temperature (IAT) is used by the ECM to adjust fuel delivery and spark timing according to incoming air density.
MAP - Range 11 to 105 kPa / 0.00 to 5.10 Volts
The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure which results from engine load and speed changes. As intake manifold pressure increases, the air density in the intake manifold also increases and additional fuel is required.
FUEL EVAP PURGE - Tech 1 Range 0-100%
A proportional signal used to control the evaporative emission canister purge function. 0% implies the valve is commanded fully closed while 100% implies that the valve is fully open.
THROT POSITION - Range 0-5.10 Volts
Used by the ECM to determine the amount of throttle demanded by the driver. Should read 0.23 to 0.59 volt at idle to above 4 volts at wide open throttle.
THROTTLE ANGLE - Range 0 - 100%
Computed by the ECM from TP sensor voltage (throttle position) and should read 0% at idle and 100% at wide open throttle. Refer to DTC 21 if TP sensor is not 0% at idle.
HEATED OXYGEN SENSOR - 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."
"OPEN / CLOSED LOOP" - Tech 1 Displays Open or Closed
"Closed Loop" displayed indicates that the ECM is controlling fuel delivery according to oxygen sensor voltage. In "Open Loop," the ECM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on TP sensor, coolant, and MAP sensor inputs only.
SHORT TERM FUEL TRIM - Range 0-255
Short term fuel trim represents a short-term correction to fuel delivery by the ECM 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 below 450 mV, indicating a lean air / fuel mixture, short term fuel trim will increase to tell the ECM to add fuel. If the oxygen sensor voltage stays mainly above the threshold, the ECM will reduce fuel delivery to compensate for the indicated rich condition.
LONG TERM FUEL TRIM - Range 0-255
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 condition exists and the ECM 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" or "YES"
-If the fuel trim enable system is learning "YES" the fuel trim is responding to the short term fuel trim. If fuel trim reads "NO," then long term fuel trim will not respond to changes in short term fuel trim.
SPARK ADVANCE - Tech 1 Range -90° to 90°
This is a display of the spark advance IC calculation. The ECM calculates and then provides all spark advance to the ignition system. The ECM computes the desired spark advance using data such as engine temperature, RPM, load, vehicle speed, and operating mode.
VEHICLE SPEED - Range 0-255 km/h, 0-255 mph
The vehicle speed sensor signal is converted into km/h and mph for display.
KNOCK RETARD - Range 0° to 45°
Indicates the amount of spark advance the ECM is removing from IC in response to the Knock Sensor (KS) signal.
KNOCK SIGNAL - Tech 1 Displays "YES" or "NO"
Indicates whether or not a knock signal is being detected by the ECM. Should display "NO" at idle.
SYSTEM VOLTAGE - Range 0.0 to 25.5 Volts
This represents the system voltage measured by the ECM.
FUEL PUMP VOLTS - Range 0 to 25.5 Volts
ECM monitors fuel pump voltage to compensate fuel delivery in the event of low voltage.
EGR DESIRED POS. - Range 0 to 100%
The EGR valve position that is being commanded by the ECM. The ECM uses various inputs to calculate the desired EGR pintle position.
EGR ACTUAL POS. - Range 0 to 100%
A feedback signal to the ECM that indicates EGR valve pintle position. Actual pintle position is determined by the input of the EGR pintle position sensor.
EGR PINTLE POS. - Range 0 to 5.10 volts
EGR position is a voltage feedback signal to the ECM that gives the position of the EGR valve. As EGR pintle position is increased, EGR position voltage increases.
EGR DUTY CYCLE - Range 0 to 100%
Used to control EGR function. 0% implies the valve is commanded fully closed, while 100% implies that the valve is fully open.
IDLE AIR CONTROL - Range 0-255
Displays the commanded position of the idle air control pintle in counts. The higher the number of counts, the greater the commanded idle speed. Idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM.
FAN CONTROL ECM D11 - Tech 1 displays OFF / ON
This will display "ON" when the ECM enables high speed fans.
FAN CONTROL ECM C6 - Tech 1 displays OFF / ON
This will display "ON" when the ECM enables low speed fans, and when the ECM enables high speed fans.
A/C FAN REQUEST - The Tech 1 Will Display "NO / YES"
If A/C system pressure is high, a signal will be sent to the ECM, and the Tech 1 will display "YES."
A/C REQUEST - Tech 1 Displays "YES" or "NO"
Represents the state of the A/C request from the control head.
A/C CLUTCH - The Tech 1 Will Display "ON / OFF"
When an A/C request is received, the ECM will activate the A/C clutch, and the Tech 1 will display "ON."
AIR PUMP RELAY - The Tech 1 Will Display "ON / OFF"
When all conditions for secondary air have been met, the ECM will activate the AIR relay and the Tech 1 will display "ON."
AIR CONTROL
When the ECM directs air to the exhaust ports, the scan tool will indicate "port." When air is directed away from the exhaust ports, the scan tool will indicate "divert."
1-4 SHIFT ACTIVE
The Tech 1 Will Display "YES / NO"- When all conditions have been met for a forced 1st to 4th gear shift, the ECM will activate the 2nd and 3rd gear blockout relay and the Tech 1 will display "YES."
OIL TEMPERATURE - Range -37°C to -215°C, -35°F to 41 9°F - The Tech 1 will display the engine oil temperature based on the engine oil temperature.
SEC VAC - Range 0 to 83 kPa, (0 to 5.10 volts)
The Tech 1 will display the amount of vacuum being applied to the secondary air inlet valve actuators.
POWER SWITCH
The Tech 1 Will Display "NORMAL / FULL" - When the power switch has been turned to the full power position, the Tech 1 will display "FULL."
SECONDARY SYSTEM
The Tech 1 Will Display "ON / OFF"
When the ECM has commanded all secondary system components on, the Tech 1 will display "ON."
FEDS / PASS-Key
An input from the CCM that tells the ECM to enable the injectors if the proper signal is received. The Tech 1 will normally display "Enabled." If the PASS-Key� test has failed, the display will switch to "Disabled" and the fuel system may be disabled. Refer to SEC~ON 8D for more information.
SECONDARY AIR INLET VALVE
The Tech 1 Will Display "ON / OFF" - When the ECM has activated the secondary air inlet solenoid valve, the Tech 1 will display "ON."
CALIBRATION ID - Range 0 to 9999
The PROM identification describes the particular PROM being used in the ECM. The Tech 1 display number is not the service part number.
TIME FROM START - Range 0:00:00 to 18:12:15 HR / MIN / SEC
A measure of how long the engine has been running. When the engine stops, it is reset to zero.