Powertrain Control Module: Notes
The primary function of the Powertrain Control Module (PCM) is to operate the following systems:
- Fuel Delivery and Injection
- Electronic Throttle Control
- Ignition
- Secondary Air Injection and Emission Control
- Idle Speed Control
- Engine Cooling Fans
- Starting
The secondary function of the PCM is to provide on-board diagnostics. During engine operation, the PCM monitors engine sensors and their related circuits for signals that are out of the normal range. The PCM constantly compares input signal voltages from each sensor with pre-programmed values (the established high and low limits of the input sensor range). If the input signal voltage is not within the established high and low limits of the input sensor range, a Diagnostic Trouble Code (DTC) will be stored (set) in the ECM memory, where it can be displayed or cleared with a scan tool. If a DTC is related to the engine or emission system, the ECM will send a signal to illuminate the Malfunction Indicator Light (MIL) in the instrument cluster module. Each monitored circuit has an associated set of conditions that the PCM must detect before a DTC will set. It is possible that a DTC for a monitored circuit may not set, even though a malfunction has occurred. This can happen if all conditions for setting the DTC have not occurred. If a DTC is cleared with a scan tool and the conditions that caused it have not been corrected, the DTC will continue to set.