U0121 — OBD-II trouble code

A network / communication OBD-II trouble code. Below are the vehicles and failure patterns where owners report it, drawn from NHTSA complaints.

In ProblemsByVin's analysis of the NHTSA owner-complaint record, owners cite U0121 across 18 vehicle failure patterns. Diagnostic codes in complaints are reported by owners and are unverified — they point to where this code shows up, not a confirmed diagnosis. Open a page below for the full pattern (symptoms, mileage, repair costs owners cite).

Vehicles where owners report U0121 18 patterns

2020 Chevrolet Malibu

electrical — Loss of Engine Power and Complete Shutdown

2020 Jeep Gladiator

steering — Electrical/communication failures affecting multiple systems (secondary to steering safety)

2019 Chevrolet Colorado

steering — Power Steering Module Failure

2018 Buick Enclave

brakes — Complete Brake Pedal Failure

2018 Chevrolet Equinox

powertrain — Stability Control / ABS Communication Fault

2017 Mercedes-Benz C-Class

electrical — Multiple Unresolved Electrical System Codes

2015 Ford Explorer

steering — Steering Rack & Pinion Failure (Electronic Power Steering Seizure)

2014 Chevrolet Malibu

electrical — Complete Electrical Shutdown While Driving

2014 Dodge Charger

powertrain — Transmission slipping, rough shifting, loss of power during acceleration

2014 Jeep Cherokee

powertrain — 9-Speed Transmission - Hesitation, Surging, and Erratic Shifting

2014 Mazda CX-5

electrical — Battery drains due to continuous parasitic electrical load

2013 Chevrolet Malibu

electrical — Complete electrical shutdown while driving

2009 Volkswagen GTI

brakes — ABS Control Module Electrical Fault (Insufficient Ground Connection)

2008 Chevrolet Tahoe

electrical — Electrical system power loss and intermittent control failures

2006 Chevrolet Cobalt

electrical — Ignition switch failure and key stuck in ignition

2006 Dodge Charger

cruise control — Post-refuel stalling

2006 Jeep Liberty

fuel system — Air pocket in fuel system / loss of fuel prime

2006 Toyota RAV4

steering — Loss of power steering while driving

Codes are pulled from what owners wrote in their NHTSA filings — they're allegations, not a shop diagnosis. Always confirm with a live scan. Browse all diagnostic codes →