P0987: Jeep's fourth-clutch hydraulic test lacks confirmation

P0987 is identified as a fourth-clutch, or 4C, hydraulic pressure test failure in the 2002 WJ/WG 45RFE/545RFE manual. This gives application-specific meaning to the catalog's pressure sensor/switch E circuit description. It should not be interpreted as a generic instruction to replace a sensor labeled E.

The test deliberately asks for a response

In a forward gear above the stated engine-speed boundary, the TCM briefly commands pressure into an otherwise unpressurized clutch circuit and checks for closure of its pressure switch. The check follows a shift and repeats periodically. Two missed closures set the documented fault. A failed response can reflect pressure delivery, switch feedback or the wiring connecting that feedback to the controller.

The factory sequence prioritizes related line-pressure faults and related gear-ratio or pressure-switch faults. It also examines line-pressure-sensor connection quality before using dedicated simulation equipment. This guards against treating an unreliable pressure reading as proof of an internal hydraulic defect.

Once the feedback path is assessed, contamination in the transmission pan changes the next decision. The manual calls for resolving the source of excessive debris before considering the remaining valve-body and solenoid/range-sensor possibilities. A clean external electrical test is therefore a reason to continue diagnosis, not proof that every internal component is healthy.

Completing the work

Repair verification should establish the expected 4C response under the specified workshop procedure. Do not attempt to trigger this test with improvised driving or pressure checks. The described logic belongs to the cited Jeep five-speed diagnostic branch and cannot establish applicability to other P0987 vehicles.

Source: DaimlerChrysler 2002 WJ/WG transmission diagnostics, physical PDF pages 162–167. The original PDF is also available as WG/02wget.pdf in the factory-manual archive.