General Parameters

NOTE: These parameters indicate engine and vehicle speed, O2 sensor operation, and overall system condition.



ENGINE SPEED
RPM - XXXX RANGE: 0 TO ENGINE MAXIMUM

RPM is the measurement of engine speed. It is computed internally by the logic module, based on ignition reference pulses. RPM is always shown at the left side on the top line of the scanner display.


OXYGEN SENSOR VOLTAGE
O2V - X.XX RANGE: 0 TO 4.98 VOLTS

The exhaust gas oxygen (02) sensor is the primary sensor that indicates whether the engine is running rich or lean. The O2 sensor generates a voltage signal that ranges from 0 volt to 1 volt or a little over 1 volt (0 to 1000 millivolts - mv). The scanner displays readings in decimal fractions of a volt, such as 0.75 volt (which is the same as 750 millivolts). O2(v) - X.XX is always shown in the center of the top line on the scanner.

A high signal indicates a inch exhaust; a low signal indicates a lean exhaust. In normal operation, the O2 sensor voltage ranges from about 0.10 to 1.00 volt. The O2 sensor must be hot (above 500 F), and the logic module must be controlling the engine in closed loop before it will respond to the sensor signal

Although the scanner can display voltage up to almost 5 volts, the sensor cannot generate more than about 1 volt. You should not see O2 voltage go much above 1.0 or 1.1 volts in fully rich conditions.


VEHICLE SPEED
VEH SPEED (MPH) - XXX
RANGE: 0 TO VEHICLE MAXIMUM
VEH SPEED (KPH) - XXX

VEH SPEED is the measurement provided by the vehicle speed sensor (VSS) pulses to the logic module. The logic module calculates the actual speed. You can change the measurement units on the scanner from miles per hour (MPH) to kilometers per hour (kPH). The preset value is MPH.

The VSS is a pulse-generator switch that sends 8 pulses per revolution of the speedometer cable. The logic module uses VSS signals and Throttle Position Sensor (TPS) signals to determine if the vehicle is standing at idle or decelerating with a closed throttle.

On late-model vehicles, the VSS signal also is used to control torque converter clutch (TCC) engagement.


CHECK ENGINE LAMP
CHECK ENG LAMP - XXX RANGE: ON - OFF

On 1989 and later vehicles, this is an output signal from the logic module to the instrument panel CHECK ENGINE lamp. If the parameter reads ON, the panel lamp should be on. When a system is operating normally, the reading should be OFF.


EMISSION MAINTENANCE REMINDER LAMP
EMR LAMP - XXX RANGE: ON - OFF

On 1989 and later trucks, this is an output signal from the logic module to the instrument panel EMISSION MAINTENANCE REMINDER lamp. If the parameter reads ON, the panel lamp should be on to indicate the need for scheduled emission system maintenance.


EXHAUST CONDITION
EXHAUST - XXXXXX RANGE: RICH - CENTER - LEAN)

This parameter indicates the general condition of the exhaust as measured by the O2 sensor. The parameter RICH and LEAN indications correspond to the flashing LED 1 during engine-running functional tests.