Our 2021 Ford F-150 Hybrid Encounters Failed 12-Volt Battery, Chattering Gear Selector
After a rocky start, our long-term 2021 Ford F-150 Limited hybrid test truck had a good run of towing, hauling and being a zippy, 430-horsepower luxury truck that’s accumulated more than 16,000 miles in the 11 months we’ve owned it. What recently sent our pickup in for unscheduled service (apart from problems that we caused) were two issues: a low-voltage warning that locked out features and a chattering retractable gear selector.
Related: Owning the 2021 Ford F-150
12-Volt Battery State of Charge Low
Nothing says good morning like a large flashing light on the instrument panel proclaiming “12V Battery State of Charge Low.” At around 13,500 miles, our long-term truck began consistently flashing this message when it sat overnight or longer. The battery became so low, in fact, that the truck would occasionally lock out power accessories, such as the power tailgate and power running boards.
Shortly after this message started appearing regularly, the check-engine light illuminated and triggered alerts via the FordPass mobile application: “The powertrain control system has detected the system power supply voltage is lower than desired,” the app said. There was a separate powertrain malfunction and reduced power warning, which, according to the app, “illuminates when the system has detected a powertrain or a four-wheel-drive fault.”
Our Ford dealer diagnosed the state-of-charge problem as a failed 12-volt main battery (one of the two onboard), which it replaced under warranty.
Mike Levine, Ford product communications director, told us the hybrid F-150’s 12-volt system powers everything electrical except for propulsion, which comes from the high-voltage battery powering the drivetrain. The F-150’s two 12-volt batteries — one main under the hood and one auxiliary under the backseat — power vehicle loads like the radio, windows and vehicle startup. During the low-voltage messaging, our truck remained drivable for the roughly 1,500 miles between when we first observed the issue and when we got it fixed. It never left us stranded.
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We also noticed our truck running differently, relying more on the gas engine versus electric-only power, with less overall smoothness. While it wasn’t reported during our service visit, according to the Ford communications team that investigated our truck’s service history, “the performance difference was due to a mid-installed [powertrain control module] connector.” We don’t know how the connector became “mid-installed” (which we take as being only half-connected) or why it wasn’t reported to us during our dealership service.
Either way, after the battery replacement and now fully mounted PCM connector, it’s driven much more like it once did, with a greater propensity to stay in electric-only mode. The engine’s idle-stop cycle and transmission shifting remain harsher than when it was new, but our dealership deemed both as normal operation.
The F-150 hybrid, like many hybrids and electric vehicles, uses a DC-to-DC converter that converts high DC voltages from the hybrid battery pack to power accessories and keep the 12-volt battery charged. This converter replaces the engine-driven alternator found in gas-only cars because hybrids frequently shut off their engines while operating. It’s not uncommon to hear about low-voltage 12-volt batteries prematurely failing or frequently discharging in hybrids and EVs, and we’ll monitor the situation as we continue to put more miles on our F-150 hybrid.
Chattering Gear Selector
The battery wasn’t our F-150’s only recent snafu. It wasn’t that cold out, but our truck’s retractable gear selector developed a case of the shivers. The intermittent chattering didn’t affect the operation of the gear selector, but it was noisy and disconcerting considering the importance of a gear selector operating correctly.
As outlined by Ford’s technical service bulletin 21-2141, our dealership reprogrammed the gearshift module using the latest software. Other symptoms we didn’t observe might have been corrected by this TSB, including not being able to shift out of Park or use the gear-selector stow feature, which retracts to enable a flat surface for laptops or hamburgers. Five hundred miles after the reprogramming, however, the gear selector has been quiet.
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