Introduction

Introduction
The P-bus is single wire serial communications bus that is used exclusively on vehicles that are equipped with ZKE III. When the E38 was introduced the objective was to reduce the complexity of the wiring harness. Peripheral modules are located in areas of the vehicle close to sensors or actuators where wiring the components separately would create an excessively large harness (e.g. door ). In some cases (e.g. Sunroof module) these peripheral modules are integrated with an actuator or switch to create one unit. The peripheral modules are connected to the GM III by the P-bus.

The P-bus is only used in the body electronics area and is very similar in communication protocol and speed to the I/K-bus. The P-bus is not designed for rapid exchange of continuous information, rather, the messages on the P-bus are short control commands. This limited message flow allows for fast reaction time by the Peripheral module (e.g. a door lock or window request).

Go to sleep mode: The ZKE III goes to sleep after the key is switched off, no messages are being sent and after 16 minutes. The GM is responsible for sending the "GO TO SLEEP" command to all of the P-bus subscribers.

Wake up: Controllers that have the capability of sending the wake-up call are the GM and the driver and passenger door modules. The wake up call is simply a P-bus low.

P-bus polling: When KL R is switched on the GM sends out a P-bus poll every 5 seconds to the modules that are coded as being installed. The P-module must respond in 5 seconds. If it does not respond the GM tries two more times. If the poll is still unanswered the GM enters it into fault memory.

Coding: The GM informs the P-modules of relevant coding data.