P0890: TCM Power Relay Sense Circuit Low

What does P0890 mean?

Some gearboxes draw their power through a relay, such as the transmission control relay in Chrysler's fuse box that feeds the solenoids. P0885 to P0887 cover the coil control of that relay, P0888 to P0892 its sense line, which reads back the switched output and compares it with the command. A dead relay leaves all solenoids without power, so the gearbox drops into its hydraulic emergency gear. P0890 means the relay delivers no voltage despite the command. Subaru documents it in four bulletins from 2022 to 2025 (Ascent, WRX, Impreza, Crosstrek, Forester): after a short trip below 0 °C condensation freezes the ignition relay contacts, the starter does not crank and P0700 often comes along. Engine module software cycles the contacts; the 2025 Forester also gets a vented relay.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Starter does not crank after a short trip in frost (Subaru)
• MIL on, P0700 in the engine module
• False oil level or other warnings

Common causes

• High Relay contacts frozen or corroded (Subaru ignition relay)
• High Outdated engine module software (Subaru)
• Medium Fuse or wire between relay and gearbox module
• Low Weak battery

Likelihood is a general estimate across vehicles; your make and model may differ.