Diesel Powertrain Control Software

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 (BUS+/BUS-). Modules communicate with the Powertrain Control Module using Standard Corporate Protocol (SCP) which determines the priority in which the signals are sent. (Refer to Standard Corporate Protocol for more information.)

Standard Corporate Protocol
The Standard Corporate Protocol (SCP) is a communication language used by Ford Motor Company for exchanging bi-directional messages (signals) between stand-alone modules and devices. Two or more signals can be sent over one circuit.

Included in these messages is diagnostic data that is output over the BUS + and BUS - lines to the Data Link Connector (DLC). This information is accessible with a scan tool. Information on this equipment is described in Diagnostic Methods.

Flash Electrically Erasable Programmable Read Only Memory
The Flash Electrically Erasable Programmable Read Only Memory (FEEPROM) is an Integrated Circuit (IC) within the PCM. This integrated circuit contains the software code required by the PCM to control the powertrain. One feature of the FEEPROM is that it can be electrically erased and then reprogrammed without removing the PCM from the vehicle. If a software change is required to the PCM, the module no longer needs to be replaced, but can be reprogrammed at the dealership through the Service Bay Diagnostic System (R) (SBDS (R)). The reprogramming is done through the DLC.

Failure Mode Effects Management
Failure Mode Effects Management (FMEM) is an alternate system strategy in the PCM designed to maintain vehicle operation if one or more 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.

FMEM operation will result in Continuous Memory DTCs during normal engine operation and when performing Key On Engine Running Self-Test Mode.

Engine RPM Limiter
The Powertrain Control Module (PCM) limits engine rpm by cutting off fuel whenever an engine rpm overspeed (3500 rpm) condition is detected. RPM limits are as follows:
^ F-Series 250/550, E-Series, and Excursion - 3500
^ F-Series 650/750 with automatic transmission - 2850
^ F-Series 650/750 with manual transmission - 2750

The purpose of the engine rpm limiter is to prevent damage to the powertrain.

Vehicle Speed Limiter

NOTE: Maximum speed may vary with load and axle ratio.

For F-250/550 applications, a diesel engine equipped vehicle is limited to a maximum speed of approximately 150 km/h (95 mph). For F-650/750 applications, the maximum vehicle speed is approximately 90 km/h (80 mph). For E150/450, the maximum vehicle speed is approximately 160 km/h (100 mph).

Powertrain Control Module
The center of the Electronic EC system is a microprocessor called the Powertrain Control Module (PCM). The PCM has a 104-pin electrical connector. The PCM receives input from sensors and other electronic components (switches, relays, etc.) and places this information in RAM or Keep Alive RAM. Based on information programmed into its memory (ROM), the PCM generates output signals to control various relays, solenoids and actuators.

Keep Alive Random Access Memory (RAM)
The PCM stores information in Keep Alive RAM (a memory integrated circuit chip) about vehicle operating conditions, and then uses this information to compensate for component variability. Keep Alive RAM remains powered when the vehicle key is off so that this information is not lost.

Power and Ground Signals

Vehicle Power
When the key is turned to the start or run position, battery positive voltage (B+) is applied to the coil of the Electronic EC Power Relay. Since the other end of the coil is wired to ground, this energizes the coil and closes the contacts of the Electronic EC Power Relay. Vehicle Power (VPWR) is now sent to the PCM and the Electronic EC System as VPWR.

Vehicle Reference Voltage
The Vehicle Reference Voltage (VREF) is a positive voltage (about 5.0 volts) that is output by the PCM. This is a consistent voltage that is used by the three-wire sensors.

Signal Return
The Signal Return (SIG RTN) is a dedicated ground circuit used by most Electronic EC sensors and some other inputs.

Power Ground
Power Ground (PWR GND) is an electric current path return for VPWR voltage circuit. The purpose of the PWR GND is to maintain sufficient voltage at the PCM.

Gold-Plated Pins
Some engine control hardware components have gold-plated pins on the connectors and mating harness connectors to improve electrical stability for low draw current circuits and to enhance corrosion resistance. The Electronic EC components equipped with gold terminals will vary by vehicle application.

NOTE: Damaged gold terminals should only be replaced with new gold terminals.