Nubira SX Hatchback L4-2.0L DOHC D-TEC MFI (1999)
Powertrain Control Module (PCM)/ Engine Control Module (ECM): Description and Operation
POWERTRAIN CONTROL MODULE/ENGINE CONTROL MODULE
The powertrain control module (PCM)/engine control module (ECM), located inside the passenger kick-panel, is the control center of the fuel injection
system. It constantly looks at the information from various sensors and controls the systems that affect the vehicle's performance. The PCM/ECM also
performs the diagnostic functions of the system. It can recognize operational problems, alert the driver through the service engine soon lamp, and store
diagnostic trouble code(s) which identify problem areas to aid the technician in making repairs.
There are no serviceable parts in the PCM/ECM. The calibrations are stored in the PCM/ECM in the programmable read-only memory (PROM).
The PCM/ECM supplies either 5 or 12 volts to power the sensors or switches. This is done through resistances in the PCM/ECM which are so high in
value that a test light will not come on when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading
because its resistance is too low. You must use a digital voltmeter with a 10 megohm input impedance to get accurate voltage readings. The PCM/ECM
controls output circuits such as the fuel injectors, the idle air control valve, the A/C clutch relay, etc., by controlling the ground circuit through transistors
or a device called a "quad-driver."
