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The PCM regulates ignition timing, air-fuel ratio, emission control devices, cooling fan, charging sys- All inputs to the PCM are converted into signals. The PCM can adapt its programming to meet chang- Fuel is injected into the intake port above the in- take valve in precise metered amounts through elec- operated injectors. The PCM fires the injectors in a specific sequence. The PCM maintains The PCM adjusts injector pulse width by opening and closing the ground path to the injector. Engine SYSTEM DIAGNOSIS The PCM tests many of its own input and output circuits. If a fault is found in a major system, the in- Multi-Point Fuel Injection—On-Board Diagnostics section of this group. CCD BUS Various modules exchange information through a communications port called the CCD Bus. The pow- POWERTRAIN CONTROL MODULE The powertrain control module (PCM) is a digital computer containing a microprocessor (Fig. 2). The PCM Inputs: • Air Conditioning Controls • Battery Voltage • Brake Switch • Camshaft Position Sensor • Crankshaft Position Sensor • Engine Coolant Temperature Sensor • Manifold Absolute Pressure (MAP) Sensor • Oxygen Sensor • SCI Receive • Speed Control System Controls • Throttle Position Sensor • Transaxle Park/Neutral Switch (automatic tran- PCM Outputs: • Air Conditioning Clutch Relay • Generator Field • Idle Air Control Motor • Auto Shutdown (ASD) and Fuel Pump Relays • Canister Purge Solenoid • Malfunction Indicator Lamp (Check Engine Lamp) • Data Link Connector • Electronic EGR Transducer • Fuel Injectors • Ignition Coil • Radiator Fan Relay • Speed Control Solenoids • Tachometer Output Based on inputs it receives, the PCM adjusts the EGR system, fuel injector pulse width, idle speed, ig- The PCM adjusts injector pulse width (air-fuel ra- tio) based on the following inputs. • engine coolant temperature • exhaust gas oxygen content (oxygen sensor) • engine speed (crankshaft position sensor) • manifold absolute pressure • throttle position The PCM adjusts ignition timing based on the fol- lowing inputs. • engine speed (crankshaft position sensor) • manifold absolute pressure • throttle position Fig. 2 PCM 14 - 146 FUEL SYSTEMS Ä |