P0890: why the Jeep factory procedure checks pressure-switch inputs

P0890 needs careful source matching. The catalog calls it a low TCM power-relay sense circuit, while the 2002 Jeep WJ/WG 45RFE/545RFE manual labels its procedure switched battery. In that documented system, the code sets when the TCM detects voltage on a pressure-switch input before it has energized the transmission relay. Do not force the generic short title onto this specific diagnostic tree.

The order of events is the clue

The check runs as the ignition moves into Run, including the transition from cranking. At that point, the controller expects the relay-fed pressure-switch inputs to follow the intended startup sequence. Voltage appearing too early directs attention toward an unwanted electrical feed. It is not a direct measurement showing low hydraulic pressure.

The manual evaluates the 2C, 4C, low/reverse, overdrive and underdrive pressure-switch sense circuits individually for shorts to voltage. That is important because several distinct wires can produce the same startup complaint. Replacing a single switch from a generic code description skips the circuit identification needed by this application.

Bound the conclusion

A normal present test requires intermittent-wiring investigation rather than assuming the historical fault is disproved. The starts-since-set information must also be interpreted according to the manual's last-code limitation.

The appropriate repair evidence identifies which input received unwanted voltage and verifies normal initialization afterward. This article describes the original Jeep procedure as written and does not resolve the catalog wording into a universal rule for P0890. Other transmissions require their own manufacturer procedure.

Source: DaimlerChrysler 2002 WJ/WG transmission diagnostics, physical PDF pages 148–151. The original PDF is also available as WG/02wget.pdf in the factory-manual archive.