P016C
Closed Loop Air/Fuel Ratio Control At Limit - System Too Lean
Closed-loop fuel trim hit its rich correction limit because mixture is structurally too lean. Likely vacuum leak, low fuel pressure, or contaminated MAF.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Common causes
Ordered by how often each turns out to be the cause.
- Vacuum leakCommon
Parts involved
- Intake System
- Fuel Pressure Regulator
- Mass Air Flow Sensor
P016C is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.