The powertrain control module (PCM) is the control center of the engine controls system. The PCM constantly looks at the information from various sensors, and controls the systems that affect emissions or engine performance. The PCM also performs the diagnostic function of the system. The PCM can recognize operational problems, alert the driver through the malfunction indicator lamp (MIL), and store a diagnostic trouble code (DTC) or DTCs which identify the problem areas in order to aid the technician in making repairs.
The powertrain control module (PCM) controls most components with electronic switches which complete a ground circuit when turned ON. These switches are arranged in groups of 4 and 7, called either a surface mounted quad driver module (QDM), which can independently control up to 4 outputs, PCM terminals, or output driver modules (ODM)s, which can independently control up to 7 outputs. Not all outputs are always used.
The control module monitors the input components for circuit continuity and out-of-range values. This includes performance checking. Performance checking refers to indicating a fault when the signal from a sensor does not seem reasonable, for example, a throttle position (TP) sensor that indicates high throttle position at low engine loads or MAP voltage. The input components may include but are not limited to the following sensors:
• The vehicle speed sensor (VSS) • The crankshaft position (CKP) sensor • The knock sensor (KS) • The throttle position (TP) sensor • The engine coolant temperature (ECT) sensor • The camshaft position (CMP) sensor • The manifold absolute pressure (MAP) sensor
The output components respond to control module commands. Components where functional monitoring is not feasible will be monitored for circuit continuity and out-of-range values if applicable.
Output components to be monitored include, but are not limited to the following circuits:
• The idle air control (IAC) motor • The control module controlled EVAP canister purge valve • The electronic transmission controls • The A/C relay • The cooling fan relay • The VSS output • The MIL control • The cruise control inhibit
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