Renault DPO Transmission & Peugeot & Citroen with AL4 Transmission

Intermittent fault. Pressure regulation fault, recommendation/ variation.

Symptom, Flashing of the snow or sports light or Automatic Transmission Fault on display. In most cases the transmission will go into the downgraded mode, or limp home. In this mode the transmission is locked in third speed to enable to continue the operation of the vehicle. This is reported by some drivers as a loss of power.

The downgraded mode can be preceded by some very harsh up or down shifts. After stopping and restarting the engine, the transmission will usually return to normal operation. Most of the time the problem appears at unpredictable intervals.

The following fault code is logged in the transmission ECU: “Intermittent fault. Pressure regulation fault, recommendation/ variation”. Cause The pressure regulation fault code is triggered when the ECU senses a difference between the calculated pressure and the actual line pressure in the transmission.

The pressure difference is caused by internal leakage. Internal leaks can 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.

With help of the diagnostic computer, check the transmission line pressure solenoids. The following parameters are expected, At idle in N: 2,4 – 2,8 bars, At idle in D: 2,8 – 3,1 bars, Under full load 2200 rpm: 11,3 – 11,7 bars.

Renault DPO & PEUGEOT & CITROEN AL4 Pressure control solenoids with black connector supersede the earlier white type connector. When replacing early white solenoids with later black type both solenoids must be replaced and the ECU must be reprogrammed to suit new pulse width modulation frequency.
If there is no change in pressures test the pressure sensor and sensor supply. If the pressure sensor is faulty a constant pressure of 6,5 bars is maintained by the system.

Daewoo 4HP16
The 4HP16 unit is a reduction design copy of the ZF 4HP20. 4HP16 is produced under licence from ZF by Daewoo.
Code P0734 Gear Ratio Error In 4TH | Code P0783 3-4 Shift Error

A common cause is a failed C brake moulded piston which has either delaminated, or over stroked the bore and cut the sealing lip,
due to a worn C clutch. Replacing the C frictions, steel plate, and piston can be done in car, via end cover entry without the need to
remove the transmission from the vehicle.

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