P0AA4: Mach-E and E-Transit faults after junction-box replacement

P0AA4 normally directs attention toward a high-voltage battery contactor circuit, but Ford SSM 51705 describes a repair-history condition that changes the next step. The affected case occurs after high-voltage battery junction box replacement on 2021–2023 Mustang Mach-E or 2022–2023 E-Transit vehicles.

The previous repair is part of the diagnosis

Ford lists P0AA4 with several other possible battery energy control module faults. The vehicle may show a wrench indicator, reduced power, a Stop Safely Now message or a high-voltage battery warning in FordPass. The bulletin says BECM software may be responsible for this post-replacement condition. It does not establish a software cause for every contactor fault before any repair has occurred.

Record which codes are present in the BECM, the warnings shown and the date and details of the junction-box replacement. A previously completed hardware repair and a continuing diagnostic occurrence count are separate issues; immediately ordering another junction box would skip the bulletin’s specified software step.

The documented next step

Ford directs the workshop to run the BECM diagnostic-trouble-code occurrence-counter reset application in FDRS. This is a named service application, not simply erasing codes with a generic reader. If the concern persists, the bulletin returns the technician to normal diagnosis in Workshop Manual section 414-03A.

Follow any stop warning and arrange suitable assistance rather than testing whether reduced-power operation improves. High-voltage contactors and the junction box require trained service procedures. This source provides no owner-level electrical test and does not authorize opening the battery enclosure or bypassing a contactor.

Source and applicability

Ford SSM 51705: 2021–2023 Mustang Mach-E and 2022–2023 E-Transit after high-voltage battery junction-box replacement.

SSM 51705 — NHTSA manufacturer communication 10237965, physical PDF page 1.