Cause
Leaking or perished vacuum hose
A rubber or plastic hose in the engine's vacuum or crankcase ventilation plumbing, split, hardened or pulled off its stub. Underbonnet heat cycles rubber thousands of times, and it ends brittle — so hoses that were flexible for a decade crack all at once, usually at a bend or where a clip grips them.
A leak here is unmetered air, entering after the sensor that measures intake flow. The engine burns a mixture leaner than it intended, corrects with fuel trim until it runs out of authority, and reports a lean fault whose real cause is a pipe.
On the crankcase ventilation side the consequence is different and worse: the system stops holding the crankcase below atmospheric pressure, and pressure that used to be drawn away starts pushing outward on the oil seals — which is how a split hose becomes a leaking crankshaft seal.
They are cheap parts and they are worth replacing as a set once one has gone, because they all aged together.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (8)
Codes where this is a likely explanation first, rather than merely a possible one.
- P2563 Turbocharger Boost Control Position Sensor A Circuit Range/Performance Likely for this code High
- P2587 Turbocharger Boost Control Position Sensor B Circuit Range/Performance Likely for this code High
- P2598 Turbocharger Boost Control Position Sensor A Performance — Stuck Low Likely for this code High
- P2599 Turbocharger Boost Control Position Sensor A Performance — Stuck High Likely for this code High
- P2C33 Crankcase Pressure Sensor B Circuit Range/Performance Likely for this code Moderate
- P2C90 Crankcase Ventilation System - Hose A Disconnected Likely for this code Moderate
- P2C91 Crankcase Ventilation System - Hose B Disconnected Likely for this code Moderate
- P2675 Air Cleaner Inlet Control Circuit/Open Low
Information, not instruction
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