MULTIPLEXING
Fault finding - Introduction
88B
88B-1
188BMULTIPLEXING
Fault finding - Introduction
INTRODUCTION
Description of the multiplex network:
The multiplex network consists of a twisted pair of wires connected to several vehicle computers. The two wires are
known as Can H and Can L.
Two of the computers have an internal resistance of 120 Ω (terminating resistance):
–the airbag computer
–the injection computer
The network carries data exchanged by the computers.
The Scénic II is a new-generation multiplex vehicle; the main change is the increase in communication speed to
500 kBauds.
On the Scénic II, only one multiplex network can be diagnosed with the RENAULT tool.
The maximum number of computers on this network is 15.
PURPOSE:
●The purpose of the multiplex network test is to determine the various computers present on the vehicle's multiplex
network as well as the cause of possible inter-computer communication failures.
●It also serves to determine the functions installed in the vehicle, which are sometimes housed in various
computers (distributed functions).
●The test also checks the condition of multiplex network segments.
●The multiplex network test can also run diagnostics on computers disconnected from the multiplex network; this
provides an overview of the vehicles electronic architecture. WARNING
Fault-finding on the Scénic II can only be done with the CLIP diagnostic tool fitted with the new vehicle
connection probe cord (part no. Elé 1674 or 00 00 167 400).
Note:
A second multiplex network for the navigation system may also be present.
MULTIPLEXING
Diagnostics - Repair assistance
88B
88B-14
Diagnostics - Repair assistance
CHANGES IN SCENIC II DIAGNOSTICS
●Assistance with computer or faulty segment detection:
If the multiplex network is completely frozen, this command can isolate multiplex network segments and thereby
rule out those that respond properly to the tool. This makes it easier to pinpoint the origin of the failure.
The algorithm for help with locating faults is intended for dealing with electrical faults present solely in CAN; it is
therefore essential that connectors and computers not attached to the bus are not taken into consideration.
●A test for multiplex network faults by using physical measurements:
When a multiplex network segment has a short circuit, the computers can no longer communicate with each other
nor with the diagnostic tool. At this point, the network test is out of order.
The CLIP tool can identify several types of faults by taking electrical measurements on the CAN H and CAN L
multiplex network. It can detect a CAN L / CAN H short circuit, a CAN L / + 12 V short circuit, a CAN H / + 12 V short
circuit, and a CAN H / earth short circuit.
Then, by disconnecting the connectors and computers in the order described under the "Help with detecting
segments - computers" heading, the actual or possible segment causing the multiplex network fault can be
identified.
●Disconnecting connectors and computers:
⇒ Help with locating network faults screen
In keeping with the diagnostic tool algorithm and based on the results obtained as it unfolds, the order for
disconnecting connectors and computers recommended by the diagnostic tool will probably be as follows:
Injection, ABS, Protection and Switching Unit, automatic transmission, LPG, steering lock, electric power-
assisted steering, instrument panel, UCH, heating and ventilation system, Control and Communications
Unit, R369 Union, Driving School Unit, airbag, R2 Union, automatic parking brake.
NOTE:
The tool sometimes requests that computers not present in the vehicle concerned be disconnected; in this case,
make sure that the computer in question is not installed, and confirm as though the component concerned had been
disconnected and reconnected and continue the test.
Network physical measurements screen
With the second screen, the operator can check the status of the multiplex network after each disconnection /
reconnection procedure involving the selected connector or computer. This enables the operator to check the status
of the multiplex network after disconnecting each component.
