Powertrain Control Software
POWERTRAIN CONTROL SOFTWAREComputer Controlled Shutdown
The PCM controls the PCM power relay when the ignition is turned to the ON or START position, by grounding the PCM relay control (PCMRC) circuit. After the ignition is turned to the OFF, ACC or LOCK position, the PCM stays powered up until the correct engine shutdown occurs.
The ignition switch position run (ISP-R) circuit provides the ignition state input to the PCM. Based on the ISP-R signal the PCM determines when to power down the PCM power relay.
Diesel Engine Power Monitor (DEPM)
The DEPM strategy resides in the transmission control module (TCM) located inside of the powertrain control module (PCM). The function of the DEPM is to monitor the engine RPM when there is no power demand from the APP sensor.
Under normal engine idle operation, the DEPM value must always be higher than the engine RPM. In the event that the RPM does increase to its calibrated idle speed value following completion of deceleration fuel shutoff due to the injectors not turning off, the DEPM disables the crank and cam output signals sent by the PCM to the fuel injector control module (FICM). The fuel injector control module monitor (FICMM) input line informs the DEPM when the injectors are turned on and when the injectors are turned off. When the FICMM line is either shorted or open, the monitor strategy assumes that the fuel injectors are always turned on and sets a DTC.
Engine RPM Limiter
The PCM limits the engine RPM by cutting off fuel whenever the engine RPM limit is detected. The RPM limit is 4,000 RPM. The purpose of the engine RPM limiter is to prevent damage to the powertrain.
Flash Electrically Erasable Programmable Read Only Memory (EEPROM)
The flash EEPROM is an integrated circuit (IC) within the PCM and the FICM. This integrated circuit contains the software code required by the PCM to control the powertrain and by the FICM to control the fuel injectors. One feature of the flash EEPROM is that it can be electrically erased and then reprogrammed without removing the PCM or the FICM from the vehicle. If a software change is required to the PCM or the FICM, a new module is no longer necessary, the original module can be reprogrammed. The reprogramming is carried out through the data link connector (DLC).
Failure Mode Effects Management (FMEM)
The FMEM system is an alternate strategy in the PCM designed to maintain vehicle operation if one or more critical sensor inputs fail. When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine running strategy. The FMEM operation results in continuous memory diagnostic trouble codes (DTCs) during normal engine operation and when carrying out the key on engine running (KOER) self-test mode.
High Speed Controller Area Network (CAN)
The high speed CAN is based on SAE J2284, ISO-11898, and is a serial communication language protocol used to transfer messages (signals) between electronic control modules or nodes. Two or more signals can be sent over one CAN circuit allowing 2 or more electronic modules or nodes to communicate with each other. This communication, or multiplexing, network operates at 500k/sec (kilobytes per second) and allows the electronic modules to share their information messages.
Included in these messages is diagnostic data sent over the CAN+ and CAN- lines to the DLC. The PCM connection to the DLC is typically done with a 2-wire, twisted pair cable used for network interconnection. The diagnostic data such as self-test or PIDs can be accessed with a scan tool. Information on scan tool equipment is described in Diagnostic Methods.
Multiplexing
The increased number of modules on the vehicle dictate a more efficient method of communication. Multiplexing is the process of communicating several messages over the same signal path. This process allows multiple modules to communicate with each other through the signal path (CAN2+/CAN2-). Modules communicate with the PCM using CAN communications, to determine the priority in which the signals are sent. Refer to the High Speed Controller Area Network (CAN).
Oil Cooler Performance Monitor
The software in the powertrain control module (PCM) provides the strategy control for the oil cooler performance monitor. The oil cooler monitor compares the engine coolant temperature to the engine oil temperature during normal engine operation. The oil cooler system maintains an acceptable engine oil temperature by transferring the heat generated in the engine oil to the engine cooling system.
The oil cooler monitor is enabled after the thermostat opens, the engine oil temperature is greater than the engine coolant temperature, and the engine speed is greater than a calibrated threshold. Once the enabling conditions are met, the oil cooler monitor calculates the difference between the engine oil temperature and engine coolant temperature and compares the readings to an expected threshold. The expected threshold is dependent on the vehicle speed and engine load conditions. If the temperature difference exceeds the maximum limit for greater than a specific amount of time, DTC P012F sets and the powertrain malfunction indicator (wrench) on the instrument cluster illuminates. This monitor runs continuously once the enabling conditions are met.
Powertrain Malfunction Indicator (Wrench)
The powertrain malfunction indicator (wrench) informs the driver that the PCM has detected a non OBD related component or system concern. When this occurs a DTC is set. The powertrain malfunction indicator (wrench) turns off through an ignition reset if the conditions are no longer met. The powertrain malfunction indicator (wrench) is located in the instrument cluster. The powertrain malfunction indicator (wrench) is illuminated by a PCM message sent through the controller area network (CAN) to the instrument cluster. To clear the DTCs, a command from the scan tool must be sent to the PCM.
Vane Sweep
The PCM commands the variable geometry turbo actuator duty cycle from 15% to 85% in a step pattern to help the turbo vanes achieve full movement. Vane sweep occurs when the following conditions are present:
- The vehicle is stopped.
- The EGR is commanded off.
- The engine speed is less than 1,160 RPM.
- The engine oil temperature is greater than a calibrated value.
Vane sweep repeats approximately every hour if the previous conditions still exist. Vane sweep may occur during scan tool commanded test functions.
Vehicle Speed Limiter
NOTE: Maximum speed may vary with load and axle ratio.
The vehicle is limited to a maximum speed of approximately 153 km/h (95 mph).