ZF 4HP 16 - Automatic Transmission (European and N. American Emissions)

DTC P1871 (European and N. American Emissions)

Circuit Description

The pressure control valves 3,4,5 and 6 are precision electronic pressure regulators that control the operation of the clutches, brakes and lock-up clutch.

The valve reduces the system pressure with which the downstream solenoid valves and electrical pressure regulating valves are supplied. It is possible to use smaller solenoid valves as a result. The pressure control solenoid valves require a constant input pressure.

Conditions for Setting the DTC

* If the voltage applied to high side driver is higher than 6V with high side driver switch off status, then a fault is detected.

* Immediately after the above condition occurs.

Action Taken When the DTC Sets

* The malfunction indicator lamp (MIL) will illuminate.

* The transmission control module (TCM) will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer.

* Adopt Emergency/ Substitute mode and constant 4th gear by hydraulic control.

* After ignition OFF/ON : 3rd gear by hydraulic control. Possible P, R and N also possible.

* Power supply cut off to the pressure control solenoid valve.

Conditions for Clearing the MIL/DTC

* The MIL will turn OFF when the malfunction has not occurred after three-ignition cycle.

* A history DTC will clear after 40 consecutive warm up cycles without a fault.

* Using a scan tool can clear history DTCs.

Diagnostic Aids

When DTC P1871 sets, the possible cause of the fault could be the solenoid valve power supply line.