Multiplexing Implementation

1-58 Description and Operation

Powertrain Control Software

Multiplexing Implementation

Currently Ford Motor Company uses CAN communication language protocol to communicate with the PCM.

For additional information about the module communications network, refer to the Workshop Manual Section 418-00, Module Communications Network for Description and Operation.

Permanent Diagnostic Trouble Code (DTC)

The software stores a permanent DTC in non volatile random access memory (NVRAM) whenever a DTC is set and the MIL has been illuminated. Permanent DTCs can only be cleared by the module strategy itself. After a permanent DTC is stored, 3 consecutive test passed monitoring cycles must complete before the permanent DTC can be erased. At that time, both the permanent DTC is erased and the MIL is extinguished. The PCM clears permanent DTCs after one monitoring cycle if a request to clear DTCs is sent by the scan tool, and the test subsequently runs and passes (test must continue to pass for the entire driving cycle for continuous monitors) and a Permanent DTC Driving Cycle has been completed. A Permanent DTC Driving Cycle requires a total of 10 minutes of engine run time, consisting of 5 minutes of vehicle operation above 40 km/h (25 MPH) and 30 continuous seconds of vehicle operation at idle. After clearing DTCs, running the OBD Drive Cycle ensures that all monitors complete, the Permanent DTC Driving Cycle completes, inspection/maintenance (I/M) readiness codes are set to a ready status and any permanent DTCs are erased. A permanent DTC cannot be erased by clearing the KAM. The intended use of the permanent DTC is to prevent vehicles from passing an in-use inspection simply by disconnecting the battery or clearing the DTCs with a scan tool prior to the inspection. The presence of permanent DTCs at an inspection without the MIL illuminated is an indication that a correct repair was not verified by the on board monitoring system.

Vehicle Speed Limiter

The PCM disables some or all of the fuel injectors whenever a vehicle over speed condition is detected. The purpose of the vehicle speed limiter is to prevent damage to the powertrain. Once the driver reduces the excessive vehicle speed, the engine returns to the normal operating mode. No repair is required. However, the technician should clear the DTCs and inform the customer of the reason for the DTC.

Either excessive wheel slippage caused by sand, gravel, rain, mud, snow, ice or excessive RPM increase in neutral may cause the vehicle speed limiter to activate even though the vehicle has not exceeded the maximum speed limit.

Powertrain Control Module - Vehicle Speed Output (PCM-VSO)

The PCM-VSO speed signal subsystem generates vehicle speed information for distribution to modules and subsystems that require vehicle speed data. This subsystem senses the transmission output shaft speed with a sensor. The data is processed by the PCM and distributed as a message on the vehicle communication network.

The key features of the PCM-VSO system are to:

• infer vehicle movement from a speed sensor.

• convert transmission output shaft rotational information to vehicle speed information.

• compensate for tire size and axle ratio with a programmed calibration variable.

• distribute vehicle speed information as a multiplexed message.

The signal from a non-contact shaft sensor, such as an output shaft speed (OSS) sensor or vehicle speed sensor (VSS), mounted on the transmission is sensed directly by the PCM. The PCM converts the OSS or VSS information to 8,000 pulses per mile, based on a tire and axle ratio conversion factor. This conversion factor is programmed into the PCM at the time the vehicle is assembled and can be reprogrammed in the field for changes in the tire size and axle ratio. The PCM transmits the computed vehicle speed and distance traveled information to all vehicle speed signal users on the vehicle.

2016 Powertrain Control/Emissions Diagnosis, Gasoline Engines, 3/2015