ZF 4HP 16 - Automatic Transmission (Non-Europe or N. American Emissions)

DTC P1855 (Non-Europe or N. American Emissions)

Circuit Description

The shift solenoids are 2 identical, normally open electronic exhaust valves that control upshifts and downshifts in all forward gear ranges. These shift solenoids work together in a combination of ON and OFF sequences to control the line pressure and shift mechanisms, such as clutches and brakes.

Solenoid 2 controls the high or low of the line pressure, the flow to each clutch valve, by the operation type ON/OFF. For example, solenoid 2 is ON, line pressure will be low, 599-799 kPa (87-116 psi) (6-8 bar). Solenoid 1 is OFF, line pressure will be high, 1 599-1 799 kPa (232-261 psi) (16-18 bar). Solenoid 2 controls the oil flow to clutch valve E or lock-up clutch valve by the ON/OFF signal.

The transmission control module (TCM) monitors numerous inputs to determine the appropriate solenoid state combination and transaxle gear tor the vehicle operating conditions.

Conditions for Setting the DTC

* Solenoid wiring open

* No DTC P1853, P1854.

* Immediately after the above condition occurs

Action Taken When the DTC Sets

* The hold lamp will blink.

* The 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.

Conditions for Clearing the Hold Lamp/DTC

* The hold lamp will turn OFF when the malfunction has not occurred after 3 ignition cycles.

* 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 P1855 sets, the possible cause of the fault could be solenoid 2.