AUTOMATIC TRANSMISSION
Fault finding - Introduction
23A
23A-5V3 MR-372-J84-23A000$045.mif
AJ0 BVA
Vdiag No.: 04, 05
4. FAULT FINDING PROCEDURE (continued)
Wiring check
Fault finding problems
Disconnecting the connectors and/or manipulating the wiring may temporarily remove the cause of a fault.
Electrical measurements of voltage, resistance and insulation are generally correct, especially if the fault is not
present when the analysis is made (stored fault).
Visual inspection
Look for damage under the bonnet and in the passenger compartment.
Carefully check the fuses, insulators and wiring harness routing.
Look for signs of oxidation.
Physical inspection
While manipulating the wiring, use the diagnostic tool to note any change in fault status from stored to present.
Make sure that the connectors are properly locked.
Apply light pressure to the connectors.
Twist the wiring harness.
If there is a change in status, try to locate the source of the fault.
Inspection of each component
Disconnect the connectors and check the appearance of the clips and tabs, as well as the crimping (no crimping on
the insulating section).
Make sure that the clips and tabs are properly locked in the sockets.
Check that no clips or tabs have been dislodged during connection.
Check the clip contact pressure using an appropriate model of tab.
Resistance check
Check the continuity of entire lines, then section by section.
Look for a short circuit to earth, to + 12 V or with another wire.
If a fault is detected, repair or replace the wiring harness.
AUTOMATIC TRANSMISSION
Fault finding - Role of components
23A
23A - 9V3 MR-372-J84-23A000$135.mif
AJ0 BVA
Vdiag No.: 04, 05AUTOMATIC TRANSMISSION
Fault finding - Role of components
Role of main automatic transmission components
Automatic transmission computer:
The gearbox computer is used to manage the entire system.
Its role is to define the optimum operating mode for the automatic transmission (modify the torque transmitted to the
drive wheels by the automatic transmission), inform the driver (instrument panel, information display, buzzer) and
communicate with the other computers.
To carry out this function, the transmission computer takes account of:
–the operation of the gearbox,
–signals exchanged with other computers,
–driver requests.
Transmission oil temperature sensor:
Its role is to inform the automatic transmission computer of the transmission oil temperature.
Transmission input speed sensor:
Its role is to inform the automatic transmission computer of the turbine speed.
Transmission output speed sensor:
Its role is to inform the automatic transmission computer of the vehicle speed.
Brake light switch:
Its role is to inform the automatic transmission computer that the driver has depressed the brake pedal.
Multifunction switch:
Its role is to inform the automatic transmission computer of the gear lever position.
Shift-lock:
The role of this function is to lock the lever in position "P" and to immobilise the vehicle when stationary.
Solenoid valves:
The solenoid valves are fitted in the factory and cannot be removed from the hydraulic distributor to ensure optimum
gearbox operation, therefore they cannot be replaced separately.
The automatic transmission has two types of solenoid valve:
–2 "all or nothing" solenoid valves,
–6 "progressive" solenoid valves.
Of these 8 solenoid valves, 7 are used to control gear changes in automatic and manual modes, and one solenoid
valve controls the oil pressure in the automatic transmission hydraulic distributor.
Instrument panel display:
The purpose of this function is to manage the transmission of multiplex line signals required for the instrument panel
display.
On the instrument panel:
–a fault warning light,
–a message on the instrument panel in case of irregularity,
–an information display: gear lever position/gear engaged/brake pedal depressed indicator light/lever position in P
or N request indicator light.
On the gear lever:
–Position: P / R / N / D / M+/-,
–Shift-lock: lever lock.
MR-372-J84-23A000$135.mif
