Introduction - CAN Networking

CAN networking

Introduction

CAN networking
Cayenne model year 2003

CAN 'Controller Area Network' (data processing network)
More and more systems in the vehicle must exchange data and this in turn requires fast and trouble-free data exchange. Control modules for various systems are connected to a 'two-wire network: high/low'. Since the amount of data that can be transferred over a network is limited, the control modules must be connected to several networks.

Three main data busses and one separate CAN data bus are used in the Cayenne. The umbrella term 'CAN data bus', which is used in these instructions to represent the individual 'CAN data busses', must be replaced by the relevant 'CAN data bus, e.g. CAN drive'.

These checking instructions are only relevant for the 'CAN data busses' listed below:
- CAN drive (CAN-C)
- CAN Infotainment
- CAN comfort (CAN-B)

The 'PSM control module' and the 'combination sensor' exchange messages via the 'CAN data bus' mentioned below.

- CAN-internal
'Internal CAN' is a separate CAN data bus that does not have any physical links to the other CAN busses, i.e. 'CAN drive/CAN Infotainment/ CAN comfort'.

General instructions/safety instructions

WARNING:
Danger of damage due to improper handling of batteries and control module plug connections.
- Never disconnect battery with engine running.
- Never start engine if battery terminal clamps are not connected securely.
- Never pull off or push on plug connections for the control modules or other electronic components when the ignition is switched on
- Always disconnect the negative terminal of the battery and pull off all plug connections to the vehicle electrical system control module when carrying out welding work on the vehicle

WARNING:
Danger of injury and damage due to unusual vehicle handling when plugs or components are disconnected.
- Never disconnect plugs when the vehicle is in motion or drive the vehicle with plugs disconnected.
- Drive only with all parts fully installed and connected.

Fault code setting conditions
Fault codes can be set in several circumstances, e.g.:
- Battery disconnected
- Plug connections disconnected
- Incorrect coding
- Voltage drop
- etc.

In these circumstances, no fault is present in the system and the fault memory must be erased.

Troubleshooting procedure
Troubleshooting can only be performed when the fault is present. In other words, specific troubleshooting can only be performed in accordance with instructions (given under Diagnosis/troubleshooting for each fault code) if the entry has the status 'present' in the fault memory.

If the fault is currently 'not present', please check the following:
- Diagnostic conditions are met
- All plug connections and ground points of the affected current path are OK
- View the fault frequency counter in the Porsche System Tester II No. 9588 using the fault memory Info key [F8] under 'Extended fault memory' and try to reach conclusions about eliminating any loose contacts in the system.

Diagnostic conditions

NOTE:
Important: Always connect a suitable battery charging device to the vehicle electrical system battery before starting diagnosis. All unnecessary loads must also be switched off.

NOTE:
The fault can only be identified if the requirements listed under 'Diagnostic conditions' are met. For this reason, the specified procedure must be observed after a fault is repaired:
1. Erase fault memory
2. Satisfy the requirements listed under 'Diagnostic conditions'
3. Read out fault memory again

Possible causes of fault

NOTE: The 'possible causes of fault' that are responsible for the fault are listed here. Please note that in certain circumstances further faults can be stored in the fault memory after troubleshooting (e.g. if plugs are disconnected). After carrying out repairs, read out the fault memory of all control modules and erase any faults.

Causes of CAN faults:
- No or incorrect basic setting/adaption (control module)
- Short circuit to B+ (CAN lead)
- Short circuit to ground (CAN lead)
- Short circuit with respect to each other (CAN lead)
- Open circuit (CAN lead)
- 'High' and 'low' confused (slot in connector, or wires separated and repaired incorrectly)

Diagnosis/troubleshooting

NOTE: The fault memory Info key [F8] on Porsche System Tester II No. 9588 can be used to access the 'extended fault memory'. The following information can be displayed:

Possible fault types:
- no signal/communication
- implausible signal/please read out fault memory

This information should be saved using the Save key [F4] and printed out.

Fault status
The following status types are possible:
- present
- not present

This information should be saved using the Save key [F4] and printed out.

NOTE:
Visual inspection: During troubleshooting, please check first that the affected pins on the control module plug connection are neither damaged nor corroded. The wires and plugs of the affected components must also be checked for external damage and correct contact. Repair damaged or corroded pins if possible, otherwise replace affected pins. Repair or replace damaged wires.

NOTE: Battery positive voltage: A battery positive voltage of between 11.4 and 14.5 V is required for troubleshooting. This must be checked and ensured if necessary. Voltages must be ensured up to components or fuses (input side) on the vehicle electrical system.