Positions
A/C REQUESTED-A/C CLUTCHThe A/C Request position displays the status of the A/C signal line to the computer. The A/C Clutch position displays "ON" when the computer energizes the compressor clutch.
BARO-BAROMETRIC PRESSURE
Barometric pressure is displayed as a voltage value of 2.5 to 5.5 volts, depending upon altitude. BARO readings should be equal to MAP readings before the engine is started.
BATTERY
Display reads battery voltage at computer ignition feed.
BLM-BLOCK LEARN MEMORY CELL
There are from 2 to 16 different cells which the computer learns, depending upon engine speed and air flow. This parameter displays which cell the computer is using for fuel calculations at the present time. A value of 128 counts indicates that the fuel delivery requires no compensation to maintain a 14.7:1 air/fuel ratio.
BPW-BASE PULSE WIDTH
Displays actual injector pulse time as calculated by the computer in milliseconds (m/sec). Normal readings should be 1-4 m/sec and varying. Lower number indicates reduced fuel delivery, while higher number indicates increased fuel delivery. A fixed reading indicates open loop operation or a system malfunction.
CCP-CANISTER PURGE
Display reads status of computer command for canister purge solenoid. Reading of "on" indicates the computer signal to solenoid. On some systems, duty cycle is displayed from 0-100 percent.
COOLANT TEMPERATURE.
This position displays engine coolant temperature in degrees Celsius. This can be used to detect malfunctions in the coolant temperature circuit if readings are not consistent with engine operation.
CROSSOVER COUNT
The O2 sensor voltage fluctuates around a threshold voltage, the value of which is stored in the PROM. A counter within the computer "counts" the number of times that actual oxygen sensor voltage crosses this threshold to indicate how fast the sensor is oscillating. The crossover count is the value representing the number of times that the sensor value crosses this threshold in 1.25 seconds. A higher crossover count number indicates a fined tune mixture ratio.
DESIRED RPM
Indicates the engine speed (rpm) to which the computer is trying to control the idle.
IGN/CRANK-IGNITION SWITCH STATUS
The crank mode (on) position engages the starter. The SCAN displays the "ON/OFF" status of the ignition switch as the signal is transmitted to the computer.
EGR SIGNAL
The SCAN tool monitors only the computer drive command to the EGR solenoid. On models with Pulse Width Modulated EGR, the reading is duty cycle of computer signals from 0-100 percent. On models with an EGR solenoid, "ON" or "OFF" status of the solenoid is indicated. The normal reading with engine running at idle should be 0 or "OFF."
EGR POSITION
Indicates position of EGR valve pintle as a voltage. A normal reading is 0.3 to 2.0 volts.
EXHAUST
Indicates whether the O2 sensor is in a rich or lean operating condition. Normal displays are "RH" for rich indication and "LN" for lean indication.
FAN
This monitors the computer command to the engine cooling fan. The scanner displays "yes" when the computer energizes the fan relay. An indication should be "no" when the coolant temperature is below 222°F (106°C).
FAN REQUEST
Displays status of A/C fan control switch. The display should read "yes" when the A/C fan switch is in the "ON" position or when A/C system pressure exceeds calibrated value. The display is "no" at all other times.
IAC-IDLE AIR CONTROL
The IAC is controlled by the computer to maintain specified idle speed. The computer controls the IAC with voltage pulses (counts) and these counts are displayed in this position. The number of counts displayed represents the position the computer "thinks" the IAC is in.
INJECTOR PULSE WIDTH
Displays injector pulse width in milliseconds. Normal readings are 1 to 4 and varying.
INT-INTEGRATOR & BLM-BLOCK LEARN MEMORY
Normal readings for these positions are approximately 128. Higher readings indicate that the computer is adding fuel to the base calibration, while lower readings indicate the computer is reducing fuel delivery. The integrator (INT) reading is short term correction and the readings vary when the computer senses a need for fuel delivery correction. Block Learn Memory (BLM) is long term correction, and readings should only change if the integrator monitors a need for correction that lasts for a calibrated period of time. Normal BLM readings are 128 to 138.
KNOCK RETARD
This display indicates the number of degrees the computer is retarding the EST spark timing.
KNOCK SIGNAL
Indicates knock sensor input to the computer. The display is "yes" when a "knock" is detected and "no" when no signal is received.
LOOP STATUS (O/L--C/L)
This position indicates whether the engine control system is operating in Open Loop (O/L) or Closed Loop (C/L) mode. Most systems are designed to enter closed loop after a certain amount of run time, when the coolant temperature exceeds a specified value. This mode can be helpful in detecting intermittent opens in the O2 sensor circuit, as the SCAN tool will indicate open loop operation long before the appropriate trouble code will be set in the computer memory.
MAP-MANIFOLD ABSOLUTE PRESSURE
Indicates voltage signal from MAP sensor. Voltage readings are low when manifold pressure is low (high vacuum), and signals increase as manifold vacuum decreases. With ignition off and engine stopped, manifold pressure is equal to atmospheric pressure and voltage signals will be high (nearly 5.0 volts). With the engine running, normal readings are 1.0 to 2.0 volts.
Comparison of sensor values with readings from a known good sensor can be used to isolate a malfunctioning sensor. Sensors have a color code tab in the connector cavity, and sensors with the same colored tab have identical calibration. Readings from sensors with like identification tabs should be the same to within +/- 0.4 volt.
MAT-MANIFOLD AIR TEMPERATURE or IAT-INTAKE AIR TEMPERATURE
Indicates temperature of intake manifold air in degrees Celsius. The reading should be close to ambient temperature when engine is cold, and the value should rise as engine and underhood temperatures increase.
MPH/VSS
Displays vehicle speed by sensing pulses transmitted to the computer from the vehicle speed sensor.
O2 SENSOR VOLTAGE
Oxygen sensor voltage is displayed in millivolts (mv) from 1 to 999. If displayed voltage is consistently below 350 mv, the computer is receiving a lean signal. If voltage is consistently above 550 mv, the computer is receiving a rich mixture signal. If the reading remains fixed between 350 mv and 550 mv for a specified amount of time, a trouble Code 13 will set in the computer.
PARK/NEUTRAL SWITCH
Indicates status of park/neutral switch. Indication may vary depending upon tool manufacturer. However, it is important that the tool indicate change in status when gear selector is moved from park or neutral position, to the drive range.
POWER STEERING SWITCH
Displays status of switch. Indication may vary depending upon tool manufacturer. However, it is important that tool indicate change in status when high power steering pressure exist, such as when the steering is held against its stop.
PPSW
Indicates fuel pump feed circuit voltage. This should indicate battery voltage when the engine is cranking or running.
RPM (ENGINE SPEED)
Displays engine speed as transmitted to the computer from a sensor. This can be used to detect extra reference pulses caused by electrical interference in the reference circuit.
SPARK ADVANCE
Indicates varying degrees of spark advance.
TPS-THROTTLE POSITION SENSOR VOLTAGE
Values displayed will be voltage values from the TPS as sensed by the computer. The value at idle should be 0-1.25 volts The value at wide open throttle should be approximately 5.0 volts.
THROTTLE ANGLE
Indicates throttle position as a percent. The value should be low at idle and 100% at wide open throttle.
TCC-TORQUE CONVERTER CLUTCH
Indicates status of computer command to energize TCC. This does not indicate that the clutch is engaged, only that the computer has completed the path to ground in the clutch solenoid circuit.
TRANSMISSION/TRANSAXLE GEAR POSITION SWITCH
Indicates signal to computer from switch. Indication may vary depending upon tool manufacturer. However, it is important that tool indicate a change in status when the gear is engaged.
TROUBLE CODES
Trouble codes set in the computer memory will be numerically displayed on the SCAN tool screen.
VAC-VACUUM (DIFFERENTIAL PRESSURE) SENSOR
Indicates voltage through the vacuum sensor. Voltage reading is low when vacuum is low, and voltage increases as vacuum increases. With ignition on and engine stopped, the reading should be under 1.0 volt. With the engine idling, high vacuum, the reading should be over 3.0 volts. Comparison of sensor values with readings from a known good sensor can be used to isolate a malfunctioning sensor. Sensors have a color code tab in the connector cavity, and sensors with the same colored tab have identical calibrations. Values from sensors with like identification tabs should be the same to within +/- 0.4 volt.
WOT-WIDE OPEN THROTTLE SWITCH
SCAN displays ON/OFF status of WOT switch as sensed by the computer. The switch should be "ON" when the throttle is in wide open position.