Powertrain, generic (extended)

P21A1 Cylinder 6 Air-Fuel Ratio Imbalance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P21A1 marks cylinder 6, the last cylinder of an inline six or V6. The clearest example comes from the 2025 RAM 1500 with the 3.0 Hurricane twin-turbo inline six: the charge-air cooler housing had a loose crimp that let boost escape, the cylinders filled unevenly and P21A1 set together with other cylinder codes, accompanied by a whistle and lower boost; the cooler was inspected and replaced if needed. Toyota listed P219A, P219B and P219C to P21A1 for the 2015 Tacoma 1GR-FE and worked through a leak-down test to a valve job. Kia replaced high-pressure injectors and fuel lines on the 2022 Carnival 3.5 GDI, while Audi corrected a software setting on 2010 to 2012 3.0 TFSI models. A code for the last cylinder alone is no reason to suspect sensor or ECM before injector and compression are checked.

Likely causes

Charge-air cooler or boost leak (turbo engines, e.g. RAM 3.0 Hurricane)
Faulty injector at cylinder 6
Valve leakage at cylinder 6
ECM software setting (e.g. Audi 3.0 TFSI)

Symptoms

  • Check engine light on
  • Whistling noise and reduced boost with a charge-air leak
  • Possible P0306 or rough running

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–2,500
Time0–10 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injector

Related codes

P219AP219BP21A0P21A2P0306

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.