The PCM is designed to maintain exhaust emission levels to Federal/California/other standards
while providing excellent Driveability and fuel efficiency. A problem in any one of theses systems will
result in a check engine light and codes stored in memory. PCM location is determined by the
make, model and year of your vehicle. You would need to get specific wiring diagrams for your
vehicle to determine location.

Review the components and wiring diagrams in order to determine which systems are controlled by
the PCM. The PCM monitors numerous engine and vehicle functions. The following are some of the
functions that the PCM controls:
•  The engine fueling
•  The
ignition control (IC)
•  The knock sensor (KS) system
•  The evaporative emissions (EVAP) system
The secondary air injection (AIR) system (if equipped)
The exhaust gas recirculation (EGR) system
•  The automatic transmission functions
•  The generator
•  The A/C clutch control
•  The cooling fan control

Powertrain Control Module Function.

The PCM constantly looks at the information from various sensors and other inputs and controls
systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on
various parts of the system.

The PCM can recognize operational problems and alert the driver via the malfunction indicator
lamp (MIL). When the PCM detects a malfunction, the PCM stores a
diagnostic trouble code (DTC).
The problem area is identified by the particular DTC that is set. The control module supplies a
buffered voltage to various sensors and switches. The input and output devices in the PCM include
analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are
electronic switches that complete a ground or voltage circuit when turned on. Most PCM controlled
components are operated via output drivers. The PCM monitors these driver circuits for proper
operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is

Note: A flashing check engine light is a government specific function that indicates the engine has
a misfire that is severe enough to cause catalytic converter damage. Quick diagnosis and repair
are needed to prevent catayltic converter failure to avoid this costly repair.

How to scan for computer trouble codes
More Auto Repair Answers, Questions And Help
                                 Electrical Testing                    Belt Diagrams              Mustang Engine Overhaul              All about Tires
Vehicle electrical testing        Serpentine belt diagrams        Ford Mustang 5.0 engine overhaul high performance        Tire number descriptions

Engine Operation
2.2L  3100 / 3400 
3.5L  3800 
4200  4.3L Vortec

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Powertrain Computer Operation And Description
Although it is common for a mechanic or any individual to blame the computer for any specific
problem on a car or truck, the fact is that aside from certain situations, the PCM is not normally the
cause. Maybe because it is easy to just blame a computer or it still is thought as a 'black box', or
people just do not understand how a vehicle system works. The fact is that most computer related
problems are caused by failed sensors or bad wiring.

Connection problems at sensors are a common cause of a check engine light. Also remember that
one system can effect another, so finding the root cause of a problem may fix multiple problems at

Don't just jump to the conclusion of a bad computer because a problem is hard to diagnose. Proper
knowledge of a particular system, proper diagnostic tools such as wiring schematics and electrical
test equipment are required to properly diagnose todays car and trucks.