About Monitored Circuits

MONITORED CIRCUITS

The Powertrain Control Module (PCM) is able to monitor and identify most driveability related trouble conditions. Some circuits are directly monitored through PCM feedback circuitry. In addition, the PCM monitors the voltage state of some circuits and compares those states with expected values. Other systems are monitored indirectly when the PCM conducts some type of a rationality test to identify problems.

Although most subsystems of the powertrain control module are either directly or indirectly monitored, there may be occasions when diagnostic trouble codes are not immediately identified.

For a trouble code to set, specific conditions must be met and unless these conditions are encountered, a code will not set. For example, the Speed Control Solenoid Circuits trouble code will not set unless the system is active (speed control is turned on, the brake is off, and mph > 35).

When a trouble code identifying a problem in an emission related system is set, the Check Engine lamp in the dash will turn on. Conversely, any other trouble code will set without illuminating the Check Engine lamp.

NOTE: The Powertrain Control Module (PCM) can detect certain faults in its systems, the following is a list of the types of faults the PCM can detect.

Open or Shorted Circuit - The PCM can determine if the input signal from the sensor is within its range and if the sensor circuit is open or shorted.

Output Device Current Flow - The PCM can see if the output devices are hooked up. If a problem exists with an output devices' circuit, the PCM can determine if it is open, shorted high, or shorted to ground.

Oxygen Sensor - Once the system has entered closed loop, the PCM checks that the oxygen sensor is switching between rich and lean.