1991 Chevrolet Caprice Classic V8-350 5.7L VIN 7 TBI Copyright © 2010, ALLDATA 10.20 Page 1
Computers and Control Systems: Scan Tool Testing and Procedures
Positions
A/C REQUESTED-A/C CLUTCH
The 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
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 specified in ELECTRICAL
AND ELECTRONIC SPECIFICATIONS or ADJUSTMENT PROCEDURES. 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 percent 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.
Я всё таки вынужден ещё раз извинится, но Олдата пишет, что скнер должен показывать угол зажигания и угол на сколько откручивает кнок. Я не знаю кому верить(творческий тупик). У мну на Флите дешёвенький китаец показывает и то и то.
