For 1990-2009 cars only
ECM Data Description: The following information will assist
in diagnosing emission or driveability problems. A first technician can view the displays
while the vehicle is being driven by second technician. Refer to Powertrain On-Board
Diagnostic System Check for addition information.
A/C Clutch: The A/C relay represents the commanded state of the A/C clutch control relay. The A/C clutch should be engaged when the scan tool displays ON.
A/C Pressure: The A/C high side displays the pressure value of the A/C refrigerant pressure sensor. The A/C high side helps to diagnose the diagnostic trouble code (DTC) P0533.
A/C Request: The A/C request represents whether the air conditioning is being requested from the HVAC selector. The input is received by the instrument panel cluster and then sent serial data to the ECM and finally to the scan tool over serial data.
Air Fuel Ratio: The air fuel ratio indicates the air to fuel ratio based on the oxygen sensor (O2S) inputs. The ECM uses the fuel trims to adjust fueling in order to attempt to maintain an air fuel ratio of 14.7:1.
BARO: The barometric pressure (BARO) sensor measures the change in the intake manifold pressure which results from altitude changes. This value is updated at ignition ON and also at wide open throttle (WOT).
Base Injection PWM: Indicates the base pulse width modulation (PWM) or ON time of the indicated cylinder injector in milliseconds. When the engine load is increased, the injector pulse width will increase.
Calculated Air Flow: The calculated air flow is a calculation based on manifold absolute pressure. The calculation is used in several diagnostics to determine when to run the diagnostics.
Desired Idle Speed: The ECM commands the idle speed. The ECM compensates for various engine loads in order to maintain the desired idle speed. The actual engine speed should remain close to the desired idle under the various engine loads with the engine idling.
Engine Coolant Temperature: The engine coolant temperature (ECT) sensor sends engine temperature information to the ECM. The ECM supplies 5 volts to the engine coolant temperature 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 voltage which it interprets 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 Desired Position: The desired exhaust gas recirculation (EGR) position is the commanded EGR position. The ECM calculates the desired EGR position. The higher the percentage, the longer the ECM is commanding the EGR valve ON.
Engine Load: Indicates engine load based on manifold absolute pressure. The higher the percentage, the more load the engine is under.
Engine Run Time: The engine run time is a measure of how long the engine has been running. When the engine stops running, the timer resets to 0.
Engine Speed: Engine speed is computed by the ECM from the fuel control reference input. It should remain close to desired idle under the various engine loads with the engine idling.
Fan: The fan control (FC) relay is commanded by the ECM. The FC relay displays the command as ON or OFF.
Fuel Level Sensor: The fuel level sensor monitors the fuel level in the tank. The fuel level sensor monitors the rate of change of the air pressure in the EVAP system. Several of the enhanced EVAP system diagnostics are dependent upon the correct fuel level.
Fuel System Status: The closed loop is displayed indicating that the ECM is controlling the fuel delivery according to the oxygen sensor (O2S) voltage as close to an air/fuel ratio of 14.7:1 as possible.
IAC Position: The scan tool displays the ECM command for the idle air control (IAC) pintle position in counts. The higher the number of counts, the greater the commanded idle speed reads. The idle air control responds to changes in the engine load in order to maintain the desired idle RPM.
Ignition 1 (Voltage): The ignition volts represent the system voltage measured by the ECM at the ignition feed circuit.
Intake Air Temperature: The ECM converts the resistance of the intake air temperature (IAT) sensor to degrees in the same manner as the engine coolant temperature (ECT) sensor. Intake air temperature is used by the ECM to adjust fuel delivery and spark timing according to incoming air density.
Knock Present: The KS noise channel indicates when the ECM detects the KS signal. The ECM should display NO at idle.
Long Term FT: The long term fuel trim (FT) is derived from the short term fuel trim value. The long term FT is used for the long term correction of the fuel delivery. A value of 128 counts (0%) indicates that the fuel delivery requires no compensation in order to maintain a 14.7:1 air to fuel ratio. A value below 128 counts means that the fuel system is too rich and the fuel delivery is being reduced. The ECM is decreasing the injector pulse width. A value above 128 counts indicates that a lean condition exists for which the ECM is compensating.
MAP: The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure which results from engine load and speed changes. As the intake manifold pressure increases, the air density in the intake also increases and the additional fuel is required.
Misfire History #1-4: Indicates the number of misfires that have occurred after 195 current misfires have been counted. The current misfire counter will add its misfires to the history misfire counter after 195 total misfires have taken place. If 1 cylinder is misfiring, the misfiring current counter will have 195 misfires counted before adding to its history counter. If 2 cylinders are misfiring, the misfiring current counter will add to their history counters after 97 misfires. The counter increments only after a misfire diagnostic trouble code (DTC) has been set.
Oxygen Sensor: The pre-converter oxygen sensor (O2S) reading represents the exhaust oxygen sensor output voltage. This voltage will fluctuate constantly between 100 mv, lean exhaust, and 900 mv, rich exhaust, when the system is operating in a closed loop.
Short Term FT: The short term FT 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 has mainly been 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.
Spark Advance: This is a display of the spark advance ignition coil (IC) calculation which the ECM is programming in the ignition system. It computes the desired spark advance using data such as engine temperature, RPM, engine load, vehicle speed, and operating mode.
TCC Engaged: When the brake pedal is applied, the torque converter clutch (TCC) brake switch sends a signal to the ECM to disengage the TCC.
Total Misfire Current Counter: Indicates the total number of misfires that have been detected in all the cylinders after 100 engine cycles. One cycle equals one complete 4 stroke cycle. The total misfire only increments during the steady state cruise conditions.
TP Sensor: The ECM uses the TP sensor in order to determine the amount of the throttle demanded by the vehicle's operator. The TP sensor reads between 0.36-0.96 volts at idle to above 4 volts at WOT.
Vehicle Speed: The vehicle speed sensor signal is converted into mph or km/h for display. The vehicle speed output from the ECM is 4,000 pulses per mile. The scan tool uses the serial data from the ECM to obtain vehicle speed, while the instrument panel cluster (IPC) and the chime alarm module use the 4,000 ppm output.
A/C Clutch: The A/C relay represents the commanded state of the A/C clutch control relay. The A/C clutch should be engaged when the scan tool displays ON.
A/C Pressure: The A/C high side displays the pressure value of the A/C refrigerant pressure sensor. The A/C high side helps to diagnose the diagnostic trouble code (DTC) P0533.
A/C Request: The A/C request represents whether the air conditioning is being requested from the HVAC selector. The input is received by the instrument panel cluster and then sent serial data to the ECM and finally to the scan tool over serial data.
Air Fuel Ratio: The air fuel ratio indicates the air to fuel ratio based on the oxygen sensor (O2S) inputs. The ECM uses the fuel trims to adjust fueling in order to attempt to maintain an air fuel ratio of 14.7:1.
BARO: The barometric pressure (BARO) sensor measures the change in the intake manifold pressure which results from altitude changes. This value is updated at ignition ON and also at wide open throttle (WOT).
Base Injection PWM: Indicates the base pulse width modulation (PWM) or ON time of the indicated cylinder injector in milliseconds. When the engine load is increased, the injector pulse width will increase.
Calculated Air Flow: The calculated air flow is a calculation based on manifold absolute pressure. The calculation is used in several diagnostics to determine when to run the diagnostics.
Desired Idle Speed: The ECM commands the idle speed. The ECM compensates for various engine loads in order to maintain the desired idle speed. The actual engine speed should remain close to the desired idle under the various engine loads with the engine idling.
Engine Coolant Temperature: The engine coolant temperature (ECT) sensor sends engine temperature information to the ECM. The ECM supplies 5 volts to the engine coolant temperature 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 voltage which it interprets 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 Desired Position: The desired exhaust gas recirculation (EGR) position is the commanded EGR position. The ECM calculates the desired EGR position. The higher the percentage, the longer the ECM is commanding the EGR valve ON.
Engine Load: Indicates engine load based on manifold absolute pressure. The higher the percentage, the more load the engine is under.
Engine Run Time: The engine run time is a measure of how long the engine has been running. When the engine stops running, the timer resets to 0.
Engine Speed: Engine speed is computed by the ECM from the fuel control reference input. It should remain close to desired idle under the various engine loads with the engine idling.
Fan: The fan control (FC) relay is commanded by the ECM. The FC relay displays the command as ON or OFF.
Fuel Level Sensor: The fuel level sensor monitors the fuel level in the tank. The fuel level sensor monitors the rate of change of the air pressure in the EVAP system. Several of the enhanced EVAP system diagnostics are dependent upon the correct fuel level.
Fuel System Status: The closed loop is displayed indicating that the ECM is controlling the fuel delivery according to the oxygen sensor (O2S) voltage as close to an air/fuel ratio of 14.7:1 as possible.
IAC Position: The scan tool displays the ECM command for the idle air control (IAC) pintle position in counts. The higher the number of counts, the greater the commanded idle speed reads. The idle air control responds to changes in the engine load in order to maintain the desired idle RPM.
Ignition 1 (Voltage): The ignition volts represent the system voltage measured by the ECM at the ignition feed circuit.
Intake Air Temperature: The ECM converts the resistance of the intake air temperature (IAT) sensor to degrees in the same manner as the engine coolant temperature (ECT) sensor. Intake air temperature is used by the ECM to adjust fuel delivery and spark timing according to incoming air density.
Knock Present: The KS noise channel indicates when the ECM detects the KS signal. The ECM should display NO at idle.
Long Term FT: The long term fuel trim (FT) is derived from the short term fuel trim value. The long term FT is used for the long term correction of the fuel delivery. A value of 128 counts (0%) indicates that the fuel delivery requires no compensation in order to maintain a 14.7:1 air to fuel ratio. A value below 128 counts means that the fuel system is too rich and the fuel delivery is being reduced. The ECM is decreasing the injector pulse width. A value above 128 counts indicates that a lean condition exists for which the ECM is compensating.
MAP: The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure which results from engine load and speed changes. As the intake manifold pressure increases, the air density in the intake also increases and the additional fuel is required.
Misfire History #1-4: Indicates the number of misfires that have occurred after 195 current misfires have been counted. The current misfire counter will add its misfires to the history misfire counter after 195 total misfires have taken place. If 1 cylinder is misfiring, the misfiring current counter will have 195 misfires counted before adding to its history counter. If 2 cylinders are misfiring, the misfiring current counter will add to their history counters after 97 misfires. The counter increments only after a misfire diagnostic trouble code (DTC) has been set.
Oxygen Sensor: The pre-converter oxygen sensor (O2S) reading represents the exhaust oxygen sensor output voltage. This voltage will fluctuate constantly between 100 mv, lean exhaust, and 900 mv, rich exhaust, when the system is operating in a closed loop.
Short Term FT: The short term FT 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 has mainly been 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.
Spark Advance: This is a display of the spark advance ignition coil (IC) calculation which the ECM is programming in the ignition system. It computes the desired spark advance using data such as engine temperature, RPM, engine load, vehicle speed, and operating mode.
TCC Engaged: When the brake pedal is applied, the torque converter clutch (TCC) brake switch sends a signal to the ECM to disengage the TCC.
Total Misfire Current Counter: Indicates the total number of misfires that have been detected in all the cylinders after 100 engine cycles. One cycle equals one complete 4 stroke cycle. The total misfire only increments during the steady state cruise conditions.
TP Sensor: The ECM uses the TP sensor in order to determine the amount of the throttle demanded by the vehicle's operator. The TP sensor reads between 0.36-0.96 volts at idle to above 4 volts at WOT.
Vehicle Speed: The vehicle speed sensor signal is converted into mph or km/h for display. The vehicle speed output from the ECM is 4,000 pulses per mile. The scan tool uses the serial data from the ECM to obtain vehicle speed, while the instrument panel cluster (IPC) and the chime alarm module use the 4,000 ppm output.
