The PCM, through various input sensors, monitors battery voltage, engine RPM, intake air volume, cranking signal, camshaft position, crankshaft position, intake air temperature, radiator and engine coolant temperatures, exhaust oxygen content, throttle position, EGR valve position, atmospheric pressure, gearshift lever position, clutch engagement, braking, power steering operation, and A/C compressor operation.

PCM uses this input information to control fuel injection and operation of other output devices. Spark timing is controlled by PCM.

PCM has a built-in fail-safe mechanism. If a fault occurs while driving, PCM will substitute preprogrammed values. Driving performance will be affected, but vehicle may still be driven.

PCM has a self-diagnostic function, which allows unit to store a number of trouble codes in its memory. A Malfunction Indicator Light (MIL) informs the driver of system problems. MIL is in center of instrument cluster, under engine symbol marked CHECK.

NOTE: Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by PCM. The second category covers OUTPUT SIGNALS, which are components controlled by PCM.

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.

Safety Warning

Electronic Fuel Injection

Use the Manual With the Right Hardware

When to See a Mechanic