Scan Data Definitions
INJECTOR PULSE WIDTHIn this position, the reading is given in milliseconds which is the "on" time that the ECM is commanding to the injector(s).
CLOSED LOOP/OPEN LOOP
This position will indicate whether the engine control system is operating in open or closed loop. Most systems go closed loop after a certain amount of run time, when engine coolant temperature is high enough, and the oxygen sensor becomes active.
DIAGNOSTIC TROUBLE CODES
Will display any diagnostic trouble codes stored in the ECM memory.
THROTTLE POSITION (TP) SENSOR
Values read will be the voltage as seen by the ECM. The voltage should be the TP sensor specification with the throttle closed and go up to about 5 volts with wide open throttle.
THROTTLE ANGLE
Displays in percent the amount the throttle is open.
HEATED OXYGEN SENSOR (HO2S)
The reading will be read out in millivolts (mv) with a range from 1 to 999 mv. If the reading is consistently below 350 (350 mv), the fuel system is running lean as seen by the Engine Control Module (ECM) and if the reading is consistently above 550 (550 mv), the system is running rich.
VEHICLE SPEED SENSOR (VSS)
Displays vehicle speed, useful in checking speedometer accuracy.
PROGRAMMABLE READ ONLY MEMORY (PROM) ID
In this position the last 4 digits of the PROM part number will be displayed.
REVOLUTION PER MINUTE (RPM)
Displays engine speed. Often useful if extra reference pulses are suspected. A sudden high revolution per minute indication while at a steady throttle would indicate electrical interference (EMI) in the reference circuit. This interference is usually caused by ECM wires too close to ignition secondary wires or an open electronic ignition ground circuit.
MILE PER HOUR (MPH)
Displays vehicle speed. Useful in checking speedometer accuracy.
ENGINE COOLANT TEMPERATURE (ECT)
Displays engine temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 85-95-C, then stabilize when the thermostat opens.
INTAKE AIR TEMPERATURE (IAT) SENSOR
Displays temperature of the intake manifold air. Should read close to ambient air temperature when the engine is cold, and rise as underhood and engine temperature increases.
MANIFOLD ABSOLUTE PRESSURE (MAP)
The Manifold Absolute Pressure (MAP) Sensor produces a low signal voltage when MAP is low (high vacuum) and a high voltage when the pressure is high (low vacuum). With the ignition on and the engine stopped, the manifold absolute pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as barometric pressure. Comparison of this barometric pressure reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Readings should be the same +0.4 Volt. MAP Sensors have a colored plastic insert visible in the connector cavity. Sensors with the same insert color are identical in calibration. The harness electrical connector color should also be the same as the sensor insert color.
BAROMETRIC PRESSURE (BARO)
Displays the MAP reading before the engine was started. This value will vary depending on Barometric Pressure and altitude.
EXHAUST GAS RECIRCULATION (EGR) (ON/OFF)
The exhaust gas recirculation system uses a valve controlled by vacuum to feed a small amount of exhaust gas back into the intake manifold to control formation of NOx. Like all ECM outputs the "Scan tool" only indicates that the ECM has commanded the function and does not indicate that the function has really happened.
INTEGRATOR AND BLOCK LEARN
On Fuel Injected Engines, normal readings for these positions are around 128. If higher, it indicates that the ECM is adding fuel to the base fuel calculation because the system is lean. If the numbers are below 128, the ECM is taking out fuel from the base calculation because the system is rich. The integrator is short term corrective action while the block learn portion (which is a long term correction) will only change if the integrator has seen a condition which lasts for a calibrated period of time.
BLOCK LEARN MEMORY (BLM) CELL
There are from zero to seventeen different cells which the Engine Control Module (ECM) learns at depending on revolution per minute (rpm) and manifold absolute pressure. This parameter will display what cell the ECM is using for the fuel calculation at the time.
IDLE AIR CONTROL (IAC) COUNTS
This system is used to control engine idle speed to the desired rpm, for different operating conditions. In this diagnostic test mode, the numbers will indicate what position the ECM thinks the valve is in. The ECM moves the idle air control in counts and these counts are displayed on a "Scan tool".
DESIRED REVOLUTION PER MINUTE
Indicates the rpm to which the ECM is trying to control the idle.
AIR CONDITIONING (A/C) REQUEST
Displays the state of the Air Conditioning (A/C) signal line to the ECM. Should read "YES" whenever the A/C is requested.
AIR CONDITIONING (A/C) CLUTCH
Displays "ON" when the ECM has commanded the A/C Clutch "ON".
POWER STEERING PRESSURE (PSP) SWITCH
Displays the state of switch. This reading may vary with the tool used and the type of switch installed on the vehicle. The important thing is that the reading changes state (switches) when the steering is moved against the stops.
BATTERY POSITIVE VOLTAGE
Displays the battery positive voltage detected at the ECM ignition input.
SPARK ADVANCE
This is a amount of total spark advance including the base electronic ignition timing.
START UP ENGINE COOLANT
This parameter is the engine coolant temperature at the time the engine was started.
ENGINE SPEED (RPM)
RPM calculated during a crank mode, helpful in diagnosing a NON-start condition.
BLOCK LEARN ENABLE
This value is an indication when the block learn values are being updated within the ECM program.
AIR/FUEL RATIO
This is the air to fuel ratio that is being commanded to the injectors.