Powertrain, generic · Fuel and air metering

P016B Closed Loop Air/Fuel Ratio Control At Limit - System Too Rich

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

With closed-loop control the engine module corrects the injected fuel using the oxygen sensor: short-term fuel trim reacts within fractions of a second, long-term trim stores a learned base correction per load and speed range. Positive values mean fuel is being added because the mixture was lean, negative values mean fuel is being removed; around ±10 % is normal. P016B means the mixture control as a whole has reached its lower limit: it already removes as much fuel as allowed and the mixture is still rich. In substance it matches P0172, but without a bank reference – for manufacturers whose strategy evaluates the control loop as a whole. CARB requires a fault once the adaptation has used up its range. No manufacturer document using exactly this code was found; Hyundai documents the lean counterpart P016C. Typical causes are those of a rich mixture: excessive fuel pressure, leaking injectors or an open purge valve.

Likely causes

Fuel pressure too high / high-pressure pump or regulator fault (direct injection)
Leaking injectors
Purge valve open
Oxygen sensor or air flow/pressure sensor offset, control module software

Symptoms

  • Check engine light on (after two drive cycles)
  • Poor cold start, rough idle
  • Higher consumption, fuel smell
  • Often together with P0172

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–4 h

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

Parts involved

fuel systemfuel injectorsevap purge valve

Related codes

P016CP016AP0172P0175

References: law.cornell.edu, static.nhtsa.gov.