OBD-II reference

All 9.533 generic OBD-II codes, explained in detail.

Causes, inspection steps and sources — a comprehensive DIY archive. Created and maintained with love for the detail. Good luck and have fun!

Powertrain generic / SAE

P016B

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

Closed-loop fuel trim hit its lean correction limit because mixture is structurally too rich. Likely fuel pressure too high, leaking injector, or O2 sensor reporting too lean.

SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number1 / 6B

Possible causes

  • Injector leaking high

Symptoms

  • Check engine light on
  • Increased fuel consumption
  • Black smoke from exhaust on acceleration
  • Smell of unburned fuel, fouled spark plugs

Inspection / repair

  • Difficulty: hard
  • DIY: shop recommended
  • Estimated cost: 150–2000 €
  • Estimated time: 1–6 h
  • Component: fuel pressure regulator
  • Component: fuel injectors
  • Component: oxygen sensor
  • MIL / check engine light
  • emissions-relevant
  • drive cycle required
  • limp mode possible

Sources

References

How to read OBD-II codes

The first letter names the vehicle system, the second digit distinguishes generic from manufacturer-specific, the remaining digits group fault area and number.

PPowertrain: engine, transmission, emissions
BBody: chassis trim, comfort, interior
CChassis: suspension, brakes, steering
UNetwork: CAN, control modules, communication