3500 4x4 Pickup L6-359 5.9L DSL Turbo (1996)
Powertrain Control Module: Description and Operation
On-Board Diagnostics
ON BOARD DIAGNOSTICS
The Powertrain Control Module (PCM) has been programmed to monitor many different circuits of the fuel injection system. This monitoring is
called "on-board diagnosis."
Certain criteria, or "arming conditions," must be met for a trouble code to be entered into the PCM memory. The criteria may be a range of: engine
rpm, engine temperature, and/or input voltage to the PCM. If a problem is sensed with a monitored circuit, and all of the criteria or arming
conditions are met, a trouble code will be stored in the PCM.
It is possible that a trouble code for a monitored circuit may not be entered into the PCM memory even though a malfunction has occurred. This
may happen because one of the trouble code criteria (arming conditions) has not been met.
The PCM compares input signal voltages from each input device with specifications (the established high and low limits of the range) that are
programmed into it for that device. If the input voltage is not within specifications and other trouble code criteria (arming conditions) are met, a
trouble code will be stored in the PCM memory.
The On Board Diagnostics have evolved to the second Generation of Diagnostics referred to as OBDII. These OBDII Diagnostics control the
functions necessary to meet the requirements of California OBDII and Federal OBD regulations. These requirements specify the inclusion of a
malfunction indicator light (MIL) located on the instrument panel for all 1994 and subsequent model-year passenger cars, light duty trucks, and
medium-duty vehicles. The purpose of the MIL is to inform the vehicle operator in the event of malfunction of any powertrain components which
can affect emissions and which provide input to, or receive output from, the engine controller module.
Control of OBDII functions is separated into two areas: the Task Manager and the Comprehensive Component Manager.
Task Manager
The Task Manager controls the execution of some component/systems tests, control of MIL illumination, storage of fault codes, and storage of
vehicle data at time of fault detection (freeze frame). This routine performs the following monitoring requirements:
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Fuel System Monitoring
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Misfire Detection
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EGR System Monitor
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Oxygen Sensor Upstream Heater Monitor
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Oxygen Sensor Upstream Monitor
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Evaporative System Monitor
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Catalyst Monitor
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Purge Flow Monitor
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02 Heater Downstream Monitor
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02 Sensor Downstream Monitor
Another function of the task manager is control of the Disable Tables. These tables are used to discontinue testing when a condition specified
in the tables are met. Testing of a component or system is disabled if a fault or failure occurs which would render the test useless. (For
example, the "Catalyst Monitor" test will not be run unless the "O2 Sensor" test has passed.)
Comprehensive Component Manager
The Comprehensive Component Manager controls the testing of all powertrain components/ systems which can affect emissions and were not
otherwise tested by the Task Manager. This routine is organized into three areas:
D3 and K4 CIRCUIT CHECKS - Performed on sensor inputs connected to the D3 and K4 to determine out-of-range or high/flow input
conditions. Performed on outputs to check for open/short conditions. The components tested are:
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Idle Air Control (IAC) Open/Short Circuit
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Generator Field
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Torque Converter Clutch (TCC) Solenoid
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Fan Relay
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A/C Relay
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Air Switch / Shift Lock Solenoid
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Transmission Relay Output
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Automatic Shutdown (ASD) Relay
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Fuel Pump Relay
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EVAP Purge Solenoid
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EGR Solenoid
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Ignition Coils
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Injector Failure
Z2 CIRCUIT CHECKS - Performed on sensor inputs connected to the Z2 to determine out-of-range or high/low input conditions. Performed
on outputs to check for open/short conditions. The components tested are: