MULTIPLEXING
Fault finding - Introduction
88B
88B-2
MONITORING MULTIPLEX NETWORK OPERATION
This step is the essential starting point before any computer diagnostics.
It ensures that the network is correctly connected at the terminals of each computer and that the signal is correctly
sent to it and received by it. On the Scénic II, this function also reads the number of faults present in the computers.
The
multiplex network test function is executed automatically after vehicle selection by the user.
After the network check, the other functions become accessible.
MULTIPLEX NETWORK TEST PROCEDURE:
⇒
Communication established with the computers storing the vehicle configuration (identification read).
⇒
Vehicle configuration read in the two computers that hold the multiplex network configuration (airbag and
UCH on the SCENIC II)
⇒ List of diagnosable computers read in the two configuration computers
⇒ Computer interrogation
⇒ Physical (electronic) measurements on the CAN network. Vehicle computer power supply for diagnostics:
Vehicle card in card reader.
Press and hold (over 5 seconds) the Start button in the absence of start conditions (for example: selecting a
gear).
Connect the diagnostic tool and perform the required operations.
Important: To power the discharge bulb computers, the dipped headlights must be turned on.
MULTIPLEXING
Diagnostics - Dealing with faults
88B
88B-8
FAULTY COMPUTER
NOTES–Make sure the computers installed in the vehicle are the correct type and are
compatible with Mégane II.
–Check the power supply to the computers (earth, + battery, + accessories or + after
ignition).
Make sure that the computer wake-up mode is in full working order on the vehicle and properly assimilated
by the computers.
The wake-up mode is:
–timed power supply: UCH, instrument panel.
–+ accessories: Protection and Switching Unit, air conditioning control panel, radio, Control and
Communications Unit.
–+ After ignition: Injection, ABS, airbag, Electric Power Assisted Steering, Automatic transmission, LPG,
Steering lock, Roof control unit, Driving school unit, Automatic parking brake, Parking assistance.
–+ After ignition + dipped headlights: Xenon bulbs.
WARNING
Dialogue with the Xenon bulbs is only possible with + after ignition and the dipped headlights on.
–Switch to computer diagnostics mode.
Test of communication with computers.
⇒No communication from computers to diagnostic tool: see Fault Finding Chart 1
No communication with the computer or computers not communicating with the
diagnostic tool.
Check the connections to the computers and for no open circuit. Repair if necessary.
⇒Computers that only produce partial information when identified:
Check in the Workshop Repair Manual or Global Vehicle Base to see that the computer
really is compatible with Scénic II.
Make sure the CLIP diagnostic tool update is recent enough to handle Scénic II faults.
If after these tests no irregularity or open or short circuit has been detected, contact your Techline.
AFTER REPAIRCarry out a new multiplex network test with the diagnostic tool.
Clear the stored faults on all the computers connected to the network.
Deal with any other possible faults.
MULTIPLEXING
Fault finding - Fault finding chart
88B
88B- 11
Fault finding - Fault finding chart
CAN network communications failure
No communication on the K lineCHART 1
No communication with computers
NOTESVehicle computer power supply for diagnostics:
Vehicle card in card reader.
Press and hold (over 5 seconds) the start button in the absence of start conditions (for
example: selecting a gear).
Connect the diagnostic tool and perform the required operations.
WARNING: The dipped headlights must be switched on to power the Xenon
headlights.
Try the diagnostic tool on another vehicle.
Make sure the tool version is more recent than CD-ROM No. 32.
Check:
–The connection between the diagnostic tool and socket (connection and cable in good condition).
–The computers' power supply.
–The engine compartment and passenger compartment fuses.
Make sure the CLIP sensor is properly fed by tracks 16 (+ 12 V), and 4 and 5 (earth) of the diagnostic socket,
indicated by the two red diodes on the sensor lighting up.
Make sure that the CLIP sensor is properly connected to the computer's USB port.
Make sure that the CLIP sensor is communicating properly with the vehicle's computers; this is indicated by
the two green diodes on the sensor lighting up.
green diodes red diodes
CAN Vehicle power supply
ISO Sensor power supply
Use the diagnostic socket to check the following tracks:
track 1 + After ignition
track 16 + Battery
tracks 4 and 5 Earth
Repair if necessary.
Check line continuity and insulation:
CAN H (diagnostic socket track 6)
CAN L (diagnostic socket track 14)
With a multimeter, make sure that the voltages at the diagnostic socket terminals are:
–2.5 V between CAN H (track 6) and the earth (tracks 4 and 5)
–2.5 V between CAN L (track 14) and earth (tracks 4 and 5) (average values)
See the Help with finding short circuits on the network heading in this section for how to detect short
circuits in the vehicle's multiplex network.
Check the continuity, insulation and for absence of interference on the K line of the diagnostic socket
(track 7).
