Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
PCM Outputs - Control Signals
- Air Conditioning WOT Relay
- Auto Shutdown (ASD) Relay
- Data Link Connector
- Duty Cycle EVAP Canister Purge Solenoid
- EGR Solenoid
- Fuel Injectors
- Fuel Pump Relay
- Idle Air Control Motor
- Ignition Coils
- Malfunction Indicator (Check Engine) Lamp
- Radiator Fan Relay
- Tachometer
Based on inputs it receives, PCM adjusts fuel injector pulse width, idle speed, ignition spark advance, ignition coil dwell and EVAP canister purge operation. The PCM regulates cooling fan, and air conditioning. The PCM changes generator charge rate by adjusting generator field. The PCM also performs diagnostics. The PCM adjusts injector pulse width (air-fuel ratio) based on following inputs.
- Battery Voltage
- Coolant Temperature
- Intake Air Temperature
- Exhaust Gas Content (Oxygen Sensor)
- Engine Speed (Crankshaft Position Sensor)
- Manifold Absolute Pressure
- Throttle Position
The PCM adjusts ignition timing based on following inputs.
- Coolant Temperature
- Intake Air Temperature
- Engine Speed (Crankshaft Position Sensor)
- Manifold Absolute Pressure
- Throttle Position
The PCM also adjusts engine idle speed through idle air control motor based on following inputs.
- Air Conditioning Sense
- Battery Voltage
- Brake Switch
- Coolant Temperature
- Engine Speed (Crankshaft Position Sensor)
- Engine Run Time
- Manifold Absolute Pressure
- Throttle Position
- Vehicle Distance (Speed)
The Auto Shutdown (ASD) and fuel pump relays are mounted externally, but turned on and off by PCM.
The crankshaft position sensor signal is sent to PCM. If PCM does not receive signal within approximately one second of engine cranking, it deactivates ASD relay and fuel pump relay. When these relays deactivate, power is shut off from fuel injectors, ignition coils, heating element in oxygen sensors and fuel pump.
The PCM contains a voltage converter that changes battery voltage to a regulated 5 volts direct current to power camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5 volt direct current supply for manifold absolute pressure sensor and throttle position sensor.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.