Powertrain Control Module

The Powertrain Control Module (PCM) is located in the engine compartment. See Fig 1 or Fig 2 . The PCM is a digital computer containing a microprocessor. The PCM receives input signals from various switches and sensors referred to as PCM inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as PCM outputs. See INPUT DEVICES  and OUTPUT SIGNALS  .

Fig 1: Locating Powertrain Control Module (Neon)

Courtesy of DAIMLERCHRYSLER CORPORATION

Fig 2: Locating Inlet Air Temperature Sensor & Powertrain Control Module (PT Cruiser)

Courtesy of DAIMLERCHRYSLER CORPORATION

Based on inputs the PCM receives, the PCM adjusts fuel injector pulse width, idle speed, ignition timing and canister purge operation. The PCM regulates the cooling fans, A/C and speed control systems. The PCM changes generator charge rate by adjusting the generator field. The PCM adjusts injector pulse width (air/fuel ratio) based on the following inputs.

• Battery Voltage
• Inlet Air/Intake Air Temperature Sensor
• Engine Coolant Temperature
• Engine Speed (Crankshaft Position Sensor)
• Exhaust Gas Oxygen Content (Heated Oxygen Sensors)
• Manifold Absolute Pressure
• Throttle Position

The PCM adjusts engine idle speed through the idle air control motor based on the following inputs.

• Air Conditioning Sense
• Battery Voltage
• Battery Temperature
• Brake Switch
• Engine Coolant Temperature
• Engine Speed (Crankshaft Position Sensor)
• Engine Run Time
• Manifold Absolute Pressure
• Power Steering Pressure Switch
• Transmission Gear Selection (Park/Neutral Switch)
• Throttle Position
• Vehicle Distance (Speed)

The PCM adjusts ignition timing based on the following inputs.

• Engine Coolant Temperature
• Inlet Air/Intake Air Temperature
• Engine Speed (Crankshaft Position Sensor)
• Knock Sensor
• Manifold Absolute Pressure
• Throttle Position
• Transmission Gear Selection (Park/Neutral Switch)

The Automatic Shutdown (ASD) and fuel pump relays are mounted in the Power Distribution Center (PDC), but are turned on and off by the PCM through the same circuit. The camshaft and crankshaft signals are sent to the PCM. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, power is shutoff to the fuel injectors, ignition coil, fuel pump and the heating element in each oxygen sensor.

The PCM contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts powers the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0-volt supply for the manifold absolute pressure sensor and throttle position sensor.

The PCM contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if an electronic control system failure exists. DTC may be retrieved from PCM for system diagnosis by using a scan tool. See SELF-DIAGNOSTIC SYSTEM  .