Fuel and air

P016C — Closed-Loop Air/Fuel Control at Limit: System Too Lean

Severity: medium Drive with care, to a shop

What P016C means

The engine control module keeps the air/fuel mixture near stoichiometric using oxygen sensor feedback and fuel trim adjustments. P016C sets when the trim has reached its maximum fuel-adding limit and the mixture is still lean. The cause is usually extra air, too little fuel, or a sensor giving false readings.

Symptoms

  • Check Engine light on
  • Rough idle
  • Hesitation or stumbling on acceleration
  • Loss of power
  • Poor fuel economy
  • Possible misfires
  • Higher emissions

Possible causes

  1. Intake air leak: hoses, intake manifold gasket, vacuum lines
  2. Exhaust leak ahead of the oxygen sensor
  3. Low fuel pressure: weak pump, clogged filter, bad regulator
  4. Clogged or faulty fuel injectors
  5. Faulty or contaminated oxygen sensor or MAF sensor
  6. Damaged oxygen sensor wiring or connector
  7. PCV system leak

How to diagnose

  1. Scan all codes and freeze-frame data, and address other codes first (MAF, misfires)
  2. Read short-term and long-term fuel trims at idle and at about 2,500 rpm
  3. Inspect intake ducts and vacuum lines, and smoke-test for leaks or watch trims react
  4. Inspect the exhaust for leaks near and before the O2 sensors
  5. Test fuel pressure and whether it holds after shutdown
  6. Check MAF and O2 sensor data with a scan tool and inspect wiring and connectors
  7. Check injector circuits and compare cylinder balance
  8. Clear the code after repair and road-test

Common fixes

  • Repair intake leaks: replace hoses, boots or gaskets
  • Seal or replace the leaking exhaust section
  • Replace the fuel filter or pump if pressure is low
  • Clean or replace injectors
  • Replace a faulty O2 sensor, or clean or replace the MAF sensor
  • Repair sensor wiring and connectors

Questions and answers

What does P016C mean?

The computer found the mixture too lean and the fuel trims ran out of range to fix it. Common causes are air leaks, weak fuel delivery or a bad sensor.

Can I drive with P016C?

Briefly, yes, but don't put it off. A lean mixture can cause misfires and overheat the catalytic converter.

Should I replace the O2 sensor for P016C?

Not first. Check for air leaks, fuel pressure and fuel trims first, since the sensor often just reports a real problem.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.