Diagnostics communication

The P-bus and I-bus are wired to the data link connector. Tech 2 can be connected with an adapter to the data link connector and communicates directly with the various control modules on the P-bus and I-bus. Diagnostics communication with O-bus systems takes place via the ICM, which acts as a gateway.

In a bus system, all units must be able to communicate with each other. For example, the engine cannot be started unless the ECM can receive the immobilization information broadcast by the CIM. Bus faults can be caused by a bus lead breaking. This could result in one or more systems disappearing from the bus concerned, depending on where the break in the wiring harness occurs. If a short circuit occurs in a bus lead, all systems will disappear from the bus concerned (P or I-bus). In the event of a fault in the grounding or power supply to one or more systems, these will cease to communicate. A break in the O-bus or a fault in the grounding or power supply to a control module on the O-bus will cause the entire O-bus to fail, since this is a ring bus. The only O-bus system that can be contacted in the event of a break is the ICM.

In theory, control modules connected to the bus can be considered as one large control module with a number of sensors and actuators.

Bus communication is comparable to internal control module communication. This means that it is vital to consider the entire vehicle when diagnosing faults. A fault may not necessarily lie in the system in which it becomes apparent but may be caused by a faulty sensor in another system.