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Home >> Dodge or Ram Truck >> 1993 >> W 350 Pickup L6-359 5.9L DSL >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Engine Control Module >> Description and Operation

Engine Control Module: Description and Operation

MODES OF OPERATION

As input signals to the PCM (Power Train Control Module) change, the PCM adjusts the responses sent to the output devices. There are seven modes of operation that determine how the PCM responds to the various input signals.

The PCM's purpose is to achieve optimum fuel economy and performance combined with low emission levels. The diesel fuel injection system has the following modes of operation:

- Ignition switch ON
- Engine start-up (Crank)
- Engine warm-up
- Cruise or Idle
- Acceleration
- Deceleration
- Ignition switch OFF



IGNITION SWITCH ON

When the ignition switch is turned to the ON position, the following actions occur:

- The PCM receives battery voltage and an ignition sense input. Once the PCM receives the ignition sense input, it becomes activated and begins to interact with its input and output devices.
- The PCM illuminates the Wait-To-Start lamp, and the Water-In-Fuel lamp for 2.8 seconds as a bulb check.
- The PCM will monitor the input signal from the charge air temperature sensor. If the PCM receives a signal from the charge air temperature sensor that the intake air temperature is at or less than 59°F (15°C), then the PCM will start the air intake heater preheat cycle. When the PCM starts this cycle, it illuminates the Wait-To-Start lamp until it is finished. The PCM ENERGIZES the air intake heaters by grounding the air intake heater relays.
NOTE: If the PCM receives an engine crank signal before the preheat cycle is finished, it will abort the preheat cycle and shut off the Wait-To-Start lamp.
- The PCM will illuminate the Water-In-Fuel lamp if a signal is sent to the PCM from the Water-In-Fuel sensor.
- The PCM monitors engine speed. When the engine speed is above 384 RPM, the controller determines the engine is running.




ENGINE START-UP

The following actions occur when the starter motor is engaged:

- The PCM receives a crank signal input when the starter relay is ENERGIZED.
- If the air intake preheat cycle is running, it will be aborted. The air intake heaters do not get ENERGIZED if an engine crank signal is sensed.



ENGINE WARM-UP

- The PCM will start the post-heat cycle if the intake air temperature, when the engine was started, was at or less than 59°F (15°C).
- If the air intake temperature is at or below 90°F (32°C), then the air temperature switch is closed, allowing voltage to flow to the KSB solenoid. When the intake air temperature increases above 90°F (32°C), the air temperature switch will open, DE-ENERGIZING the KSB solenoid.
- If the coolant temperature is below 60°F (16°C), the coolant temperature switch will close. When the PCM receives a signal that the coolant temperature switch is closed, it prevents the transmission from shifting into overdrive (automatic only). Once the coolant temperature reaches 60°F (16°C), the coolant temperature switch will open.
- The PCM will illuminate the Water-In-Fuel lamp if it receives a signal from the Water-In-Fuel sensor.


CRUISE OR IDLE

- The PCM monitors the intake manifold air temperature based upon input signals from the charge air temperature sensor.
- If the air intake temperature is at or below 90°F (32°C), then the air temperature switch is closed, allowing voltage to flow to the KSB solenoid. When the intake air temperature increases above 90°F (32°C), the air temperature switch will open, DE-ENERGIZING the KSB solenoid.
- If the air intake heater post-heat cycle is not finished, it will be completed in this mode.
- The Throttle Position Sensor (TPS), Engine Speed Sensor, and the Vehicle Distance (speed) Sensor inputs are used to control automatic transmission overdrive operation.
- If the coolant temperature is below 60°F (16°C), the coolant temperature switch will close. If the PCM receives a signal that the coolant temperature switch is closed, the transmission will not be allowed to shift into overdrive (automatic transmission). Once the coolant temperature reaches 60°F (16°C), then the coolant temperature switch will open and the transmission will be able to be shifted into overdrive.
- If the transmission thermo-switch is open, the transmission will not be allowed to be shifted into overdrive (automatic transmission). If the transmission thermo-switch opens while the transmission is in overdrive, then the transmission will be downshifted. The opening or closing of the transmission thermo-switch is dependant upon the temperature of the transmission fluid. The thermo-switch opens at 273°F (134°C), and closes when the transmission fluid drops to 240°F (116°C).
- The PCM will illuminate the Water-In-Fuel lamp if it receives a signal from the Water-In-Fuel sensor.



ACCELERATION

- The Throttle Position Sensor (TPS), Engine Speed Sensor and the Vehicle Distance (speed) Sensor are used to determine when the automatic transmission can be shifted into overdrive.
- If the coolant temperature is below 60°F (16°C), the coolant temperature switch will close, and the controller will prevent the automatic transmission from being shifted into overdrive. Once the coolant temperature reaches 60°F (16°C), then the coolant temperature switch will open.
- If the air intake temperature is at or below 90°F (32°C), then the air temperature switch is closed, allowing voltage to flow to the KSB solenoid. When the intake air temperature increases above 90°F (32°C), the air temperature switch will open, DE-ENERGIZING the KSB solenoid.
- If the transmission thermo-switch is open, the transmission will not be allowed to be shifted into overdrive (automatic transmission). If the transmission thermo-switch opens while the transmission is in overdrive, then the transmission will be downshifted. The opening or closing of the transmission thermo-switch is dependant upon the temperature of the transmission fluid. The thermo-switch opens at 273°F (134°C), and closes when the transmission fluid drops to 240°F (116°C).
- If the speed control system is being used, and the resume/accelerate button is held, the PCM will only allow the vehicle to accelerate at a predetermined rate. If the speed control system has been set, and the resume/accelerate button is momentarily pressed, the PCM will accelerate the vehicle at two mile per hour increments. If the brakes are applied, the PCM will de-activate the speed control system.
- The PCM will turn on the Water-In-Fuel lamp if it receives a signal from the Water-In-Fuel sensor.


DECELERATION

- The Throttle Position Sensor (TPS), Engine Speed Sensor and the Vehicle Distance (speed) Sensor inputs are used to control automatic transmission overdrive operation.
- If the coolant temperature is below 60°F (16°C), the automatic transmission will not be allowed to enter overdrive operation. Once the coolant temperature reaches 60°F (16°C), the coolant temperature switch will open.
- If the transmission thermo-switch is open, the transmission will not be allowed to be shifted into overdrive (automatic transmission). If the transmission thermo-switch opens while the transmission is in overdrive, then the transmission will be downshifted. The opening or closing of the transmission thermo-switch is dependant upon the temperature of the transmission fluid. The thermo-switch opens at 273°F (134°C), and closes when the transmission fluid drops to 240°F (116°C).
- If the air intake temperature is at or below 90°F (32°C), then the air temperature switch is closed, allowing voltage to flow to the KSB solenoid. When the intake air temperature increases above 90°F (32°C), the air temperature switch will open, DE-ENERGIZING the KSB solenoid.
- If the speed control system is being used, and the coast/set button is held, the PCM will only allow the vehicle to decelerate at a predetermined rate. If the coast/set button is released, while decelerating, the PCM will reset the speed control to the rate of speed the vehicle was traveling when the coast/set button was released.
- If the brakes are applied, the PCM will de-activate the speed control system.
- The PCM will turn on the Water-In-Fuel lamp if it receives a signal from the Water-In-Fuel sensor.




IGNITION SWITCH OFF

When the key is placed in the OFF position, the PCM still receives battery voltage. The PCM needs battery voltage at all times to keep its memory alive. The memory stores TPS value from the previous Key-on and it stores fault codes.
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