ZF 4HP 16 - Automatic Transmission (European and N. American Emissions)
DTC P1855 (European and 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, if solenoid 2 is ON, the line pressure will be low, 599-799 kPa (87-116 psi) (6-8 bar). Solenoid 1 is OFF, the line pressure will be high, 1 599-1 799 kPa (232-261 psi) (16-18 bar). Solenoid 2 controls the oil flow to the clutch valve E or the 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 for 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 malfunction indicator lamp (MIL) will illuminate.
* 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 the ignition is OFF/ON: 3rd gear by hydraulic control. P, R, and N are also possible.
Conditions for Clearing the MIL/DTC
* The MIL 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.