Flashing of the "Snow" or/and "Sports" light then the transmission went into the downgraded mode. In this mode the transmission was locked in third gear to enable to continue the operation of the vehicle following by a loss of power. The downgraded mode sometimes preceded by some very harsh [jerking] shifts. However after stopping and restarting the engine, the transmission would usually return to normal operation.
Most of the time the problem appears at unpredictable intervals. Some incidences were on a daily basis, sometimes may have weeks of trouble free operation between incidents.
At SC I was told the following fault code was logged in the transmission ECU: "Intermittent fault. Pressure regulation fault, recommendation/variation"
Being a technical person I usually ask for the explanation. I was told the pressure regulation fault code was triggered when the ECU senses a difference between the calculated pressure and the actual line pressure in the transmission. The pressure difference was caused by internal leakage. Internal leaks could be caused by mechanical wear, a leak between valve body and transmission casing, incorrect adjustment of the manual valve index spring.
The most common cause however is the pressure regulation solenoid valve.
The diagnosis was not straightforward, several operations were required to eliminate possibilities.
- Transmission fluid
- ATF level was checked in the transmission. [Note: Low or high fluid levels are equally harmful]
- ATF was placed in a clean container for examination.
- Pressure sensor
- With help of the diagnostic computer the transmission line pressure was checked.
The following parameters were observed.
At idle in N around 2.6 bars.
At idle in D around 3 bars.
Under full load 2200 rpm: 11.5 bars.
- Since there was change in pressures, no need to test the sensor and sensor supply.
- Solenoid Valves
- Pressure regulation valve and the converter lock-up valves were replaced.
- 2 seals behind the valve body are correctly fitted. The seals were not replaced.
- After fitting the valve body, the selector index spring was adjusted
- The multi-function switch was also adjusted.
- Before fitting the pan , the 2 magnets presence was assured.
- ATF was refilled and adjusted the level.
- The transmission ECU software was updated for the new solenoid valve because the older software versions are not compatible with the new Borg Warner valves.
The transmission didn't need to be overhauled or replaced because the fluid sample was normal like fresh ATF, i.e transparent. Fluid drained from a transmission that has been in operation for some time is usually dark in colour and lacks transparency, this is acceptable and not necessarily an indication of an internal fault. Caution was exercised with the fluid assessment.
Note: A faulty sensor maintain constant pressure of 6,5 bars. This would also mean that the transmission would be in Limp Home Mode and that the fault is permanent. Since the problem usually was intermittent the pressure readings would check out OK most of the time. Since no other problems have been found so far, diagnose continued...
The operations outlined obove resolved the pressure regulation problem.
If the problem couldn't be resolved Valve-body probably need to be replaced. Worse case, the whole Transmission required overhaul or replacement.
- Only use genuine Peugeot ATF.
- The fluid level must be correct.
- The correct adjustment of the manual valve index spring is very important.
- Adjust the multi-function switch after the valve adjustment.
- Cleanliness is absolutely essential when working on the transmission.
Is is good to know...
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