Trouble Codes; General Description - Ford Ranger Maintaince And Repair Manual

TROUBLE CODES

General Description

Ford Ranger/Explorer and Mountaineer vehicles employ the Electronic Engine Control (EEC) system, to
manage fuel, ignition and emissions on vehicle engines.
The Powertrain Control Module (PCM) is given responsibility for the operation of the emission control
devices, cooling fans, ignition and advance and in some cases, automatic transmission functions. Because the
EEC oversees both the ignition timing and the fuel injector operation, a precise air/fuel ratio will be
maintained under all operating conditions. The PCM is a microprocessor or small computer which receives
electrical inputs from several sensors, switches and relays on and around the engine.
Based on combinations of these inputs, the PCM controls outputs to various devices concerned with engine
operation and emissions. The engine control assembly relies on the signals to form a correct picture of current
vehicle operation. If any of the input signals is incorrect, the PCM reacts to what ever picture is painted for it.
For example, if the coolant temperature sensor is inaccurate and reads too low, the PCM may see a picture of
the engine never warming up. Consequently, the engine settings will be maintained as if the engine were cold.
Because so many inputs can affect one output, correct diagnostic procedures are essential on these systems.
One part of the PCM is devoted to monitoring both input and output functions within the system. This ability
forms the core of the self−diagnostic system. If a problem is detected within a circuit, the controller will
recognize the fault, assign it an identification code, and store the code in a memory section. Depending on the
year and model, the fault code(s) may be represented by two or three digit numbers. The stored code(s) may
be retrieved during diagnosis.
While the EEC system is capable of recognizing many internal faults, certain faults will not be recognized.
Because the computer system sees only electrical signals, it cannot sense or react to mechanical or vacuum
faults affecting engine operation. Some of these faults may affect another component which will set a code.
For example, the PCM monitors the output signal to the fuel injectors, but cannot detect a partially clogged
injector. As long as the output driver responds correctly, the computer will read the system as functioning
correctly. However, the improper flow of fuel may result in a lean mixture. This would, in turn, be detected by
the oxygen sensor and noticed as a constantly lean signal by the PCM. Once the signal falls outside the
pre−programmed limits, the engine control assembly would notice the fault and set an identification code.
Additionally, the EEC system employs adaptive fuel logic. This process is used to compensate for normal
wear and variability within the fuel system. Once the engine enters steady−state operation, the engine control
assembly watches the oxygen sensor signal for a bias or tendency to run slightly rich or lean. If such a bias is
detected, the adaptive logic corrects the fuel delivery to bring the air/fuel mixture towards a centered or 14.7:1
ratio. This compensating shift is stored in a non−volatile memory which is retained by battery power even
with the ignition switched OFF. The correction factor is then available the next time the vehicle is operated.
If the battery cable(s) is disconnected for longer than 5 minutes, the adaptive fuel factor will be lost.
After repair it will be necessary to drive the truck at least 10 miles to allow the processor to relearn the
correct factors. The driving period should include steady−throttle open road driving if possible. During
the drive, the vehicle may exhibit driveability symptoms not noticed before. These symptoms should
clear as the PCM computes the correction factor. The PCM will also store Code 19 indicating loss of
power to the controller.
TROUBLE CODES 581