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
AUTOMATIC TRANSMISSION
Fault finding - Interpretation of faults
23A
23A - 67V3 MR-372-J84-23A000$450.mif
AJ0 BVA
Vdiag No.: 04, 05
DF256
PRESENT
OR
STOREDERRATIC GEAR JUMPING
1.DEF: Hydraulic, mechanical or electrical fault on solenoid valves, deal with the
other faults first
NOTESConditions for applying fault finding procedures to stored faults:
The fault appears after:
1st case: when driving, in Drive or in Manual
ratio > ratio setpoint,
and output speed ≥ 300 rpm,
and turbine speed ≥ 300 rpm,
and engine speed ≥ turbine speed - 50 rpm,
and (if 1st with engine braking, accelerator pedal ≥ 6.25 % OR,
if 1st, accelerator pedal ≥ 30.75 % OR,
if 2nd to 6th accelerator pedal ≥ 6.25 %).
2nd case: while driving, reverse gear
ratio > ratio setpoint,
and output speed ≥ 300 rpm,
and turbine speed ≥ 300 rpm,
and engine speed ≥ turbine speed - 50 rpm,
and accelerator pedal ≥ 6.25 %.
3rd case: stationary, in Drive or in Manual
Difference between engine speed and mapping > threshold,
and engine speed increases constantly for 250 ms.
4th case: stationary, reverse gear
Difference between engine speed and mapping > 0,
and engine speed increases constantly for 250 ms.
System effects:
No engine torque transmitted to wheels.
Switch to defect mode occurs during vehicle speed safety conditions (vehicle speed
< 32 mph (54 km/h)).
The system effects will vary depending on which solenoid valve is faulty:
–If caused by brake 2 solenoid valve, system switches to fixed 2nd, 3rd or 5th gear
safe mode.
–If caused by clutch 2 solenoid valve, system switches to fixed 2nd, 3rd or 6th gear
safe mode.
–If caused by the clutch 3 solenoid valve, system switches to fixed 2nd, 3rd, 4th or 5th
gear safe mode.
–If caused by clutch 1 solenoid valve, system switches to fixed 3rd, 5th or 6th gear
safe mode.
In all cases, restarting is in 3rd gear.
If vehicle stopped in Drive, system switches to fixed 5th gear if engine speed is lower
than 2000 rpm.
If vehicle stopped in "R" mode, switching to "R" mode is done if engine speed is less
than 2000 rpm.
In reverse, moving off when "kick-down" detected.
AFTER REPAIRDeal with any other faults. Clear the fault memory.
Switch off the ignition, wait 1 minute and carry out a road test followed by another
check with the diagnostic tool.
AJ0_V04_DF256/AJ0_V05_DF256
