P0AC4: owner reports and bulletins

Powertrain (generic, all makes). We haven't written the explanation for this code yet. Below is what owners and manufacturers have filed with NHTSA.

Got P0AC4 on your scanner? Tell the mechanic your year, make, model and any symptoms and you'll get the likely cause and what to check first. Ask about this code.

What owners report to NHTSA

9 complaints filed with NHTSA mention P0AC4, 8 of them since 2015, across 2 different models. The component owners most often filed it under: fuel/propulsion system.

Most-reported models

VehicleComplaintsModel years reported
CHEVROLET VOLT82012, 2016, 2017, 2018, 2019

Manufacturer service bulletins that name P0AC4

12 technical service bulletins and manufacturer communications filed with NHTSA mention P0AC4, from 2 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:

  • CADILLAC ELR (2014, 2015, 2016), bulletin 10176301: This Preliminary Information communication provides information to the technician the steps to diagnose and repair vehicles that have Check Engine Light illuminated with an "Engine Unavailable" and "Reduced Propulsion" m…
  • CHEVROLET MALIBU (2016, 2017, 2018), bulletin 10139254: This Bulletin provides ECM reprogramming information to Correct DTC P3260 and P0AC4.
  • CHEVROLET VOLT (2016), bulletin 10135428: 27660 - Service Update. The engine may stall, followed by a Driver Information Center (DIC) message ?Action Required-Engine Not Available?. This will also cause diagnostic trouble codes P0AB9 (Hybrid/EV System Performanc…

Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.