P0801

P0801 is the electrical-circuit fault for the Reverse Inhibit Control Circuit — the TCM (or BCM on some applications) commands a solenoid or relay to physically block reverse engagement above a programmed road speed (typically 5-7 mph), and the driver circuit reads open, shorted, or out-of-spec. Cheapest-first: scan for companion codes (a lone P0801 with no P0700/P0715 is almost always external wiring), then unplug the reverse inhibit solenoid connector at the transmission and ohm the solenoid pin-to-pin. Typical PCS-B/inhibit-style solenoid spec lands 8-30 ohms cold; on/off inhibit solenoids on Subaru 4EAT/Toyota A340 spec 11-15 ohms, and infinite (open) or under 3 ohms (shorted) condemns the solenoid outright. Then ohm pin-to-ground on each leg — anything under 100k ohms to case ground on what should be a floating circuit means insulation breakdown from ATF migration up the harness. Back-probe the driver circuit with a low-amp clamp and watch for the commanded 0.5-1.5 A pulse on key-on; absent current means TCM driver fault or open wire upstream. Expensive-misdiagnosis caveat: on Chrysler 545RFE/68RFE the reverse inhibit logic lives inside the integrated solenoid pack assembly (TRS + pack on the valve body), so a clean P0801 with no movement issues frequently presents as a single-circuit code when the actual problem is the entire solenoid pack going progressively out of tolerance — replacing one wire or chasing one pin is wasted labor when the whole pack is shedding debris.

Vehicle-specific patterns: 1998-2005 Subaru Forester/Outback/Legacy with the 4EAT throws P0801 from the dropping resistor or the reverse inhibit solenoid in the valve body itself — the solenoid is accessible after pan drop, $80-150 part, plus filter and fluid. 1995-2004 Toyota 4Runner/Tacoma and early Lexus GS300/LS400 with the A340/A340E (and A343F variant) sets the equivalent OE code from the inhibitor switch on the trans range sensor going out of adjustment or developing internal corrosion — RepairPal and AAMCO both flag this as the #1 cause on those platforms, $120-250 for the switch. 2003-2010 Dodge Ram 1500/2500 with the 545RFE and later 68RFE set P0801 frequently from solenoid pack degradation at 70,000-150,000 miles — the SAE J2012 code points at one circuit but the pack as a whole is the failure, and Chrysler dealers commonly replace the full solenoid pack assembly ($500-900 parts + labor at independents per AAMCO survey data). 2007-2014 Nissan Frontier/Xterra with the RE5R05A throws it from internal harness chafe at the case connector pass-through. Estimated repair: $150 to $900.