SW1 L4-1.9L SOHC VIN 8 (1996)
Engine Control Module: Description and Operation
GENERAL DESCRIPTION:
The powertrain control module (PCM) is located in the upper dash area directly forward of the I/P cluster. It is mounted to the center dash cross car
beam and is supported on the bottom side with a PCM/ABS lower bracket.
The PCM uses signals from various sensors in order to optimize the control of the engine, transaxle, and various accessories. The PCM is a
microprocessor based computer that is the main component of the powertrain control system. The PCM contains either one or two separate controllers
located in one assembly. Manual transaxle versions contain only the engine controller (EC) while auto transaxle models contain both the EC and
transaxle controller (TC).
There are only two versions of the PCM dependent on transaxle usage:
1. SOHC (L24) and DOHC (LL0) with MANUAL transaxle (MP2/MP3).
2. SOHC (L24) and DOHC (LL0) with AUTOMATIC transaxle (MP6/MP7).
The PCM controls the following systems:
FUEL INJECTOR CONTROL
The PCM controls fuel by receiving input signals from various sensors. It then takes this information and calculates the amount of fuel required to
achieve a specific air/fuel ratio. The PCM controls the fuel flow into the engine by controlling each injector individually. This system is called
sequential fuel injection (SFI).
SPARK TIMING CONTROL
The PCM receives reference signals from the crankshaft position sensor. The PCM also uses MAP and TP to calculate the spark output signal. The
spark output signal controls the timing of the primary of the ignition coils. The PCM also provides spark retard when knock conditions are
detected by a knock sensor mounted in the engine block.
FUEL PUMP CONTROL
The PCM controls the in-tank electric fuel pump by energizing or de-energizing the fuel pump relay. When the ignition key is first turned to the
Run position, the PCM will energize the fuel pump relay, by supplying power, for approximately two seconds to pressurize the fuel system. If the
vehicle is started and engine references pulses are received from the crankshaft position sensor, the fuel pump relay will be left energized. If the
engine is not started within approximately two seconds, the relay will be de-energized. When the ignition key is turned to the Off position the fuel
pump relay will be de-energized. The fuel pump relay will also be de-energized within approximately two seconds, if crankshaft pulses are not
received. This is a safety feature, in case of an accident the fuel to the engine compartment is shut-off.
PCM FLASH PROGRAMMING
The PCM has both software and calibrations which are specific to model and option content. This information is stored in the PCM in an
electronically erasable programmable read only memory (EEPROM). Reprogramming of the PCM/EEPROM is necessary when replacing a PCM,
or when changing the EC or TC calibrations. Both the software and calibrations will be reprogrammed at the same time anytime a download is
performed.
Refer to "Tools and Equipment" for further explanation of Saturn specific tools. See: Tools and Equipment
The service stall system (SSS) provides a means of reprogramming PCM EEPROM through the System Utilities Main Menu function. The
"Service Stall System User's Guide" and/or system help (F1 = HELP) feature provides the procedure to follow for EEPROM flash reprogramming.
When possible the vehicle information contained in the original controller being replaced should be removed and installed in the new PCM. This
can only be accomplished by following the PCM Replacement functions through the SSS in the System Utilities Main Menu. if a PCM needs flash
reprogramming and the PCM is incapable of communications, the vehicle identification number (VIN), vehicle option content, and tire size will
have to be manually installed.
In the event the vehicle is not available (i.e. retailer over the counter parts sale), a bench reprogramming tool is available to flash the replacement
PCM. The tool (SA9501Z) is used in conjunction with the SSS to allow connections for flash programming. if the original PCM is available,
vehicle information should be pulled from the original and installed in the new. if the old PCM is not available or is incapable of communications,
the VIN, vehicle option content, and tire size must be installed manually.
