P2C90: Crankcase Ventilation System - Hose A Disconnected
What to do
Open the bonnet and look for a disconnected hose — this is one of the few codes where you may simply see the problem.
Your engine has a ventilation system that draws gases out of the bottom of the engine, and it has detected that one of its hoses has come off. They are usually thick plastic or rubber pipes running between the top of the engine and the intake, and a detached one is often visible.
Get it back on promptly, even though the car drives. With the hose off, pressure inside the engine has nowhere to go and starts pushing outward on the oil seals — which turns a five-minute fix into a crankshaft seal replacement if it is left.
If any work has been done on the engine recently, mention it. A ventilation hose not refitted afterwards is the single most common cause.
You may also notice rough running or a lean-mixture warning — that is the same fault, since the loose hose lets unmeasured air into the engine.
What this code means
The crankcase ventilation system has detected that hose A is disconnected.
This is one of the most useful codes in the corpus, because it names a specific physical thing that has come off — and because the consequence of leaving it is oil rather than a warning light.
The crankcase ventilation system draws blow-by gas out of the engine's bottom end and returns it to the intake, keeping the crankcase slightly below atmospheric pressure. When a hose in that circuit comes off, three things happen at once.
- Unmetered air enters the intake, so the mixture goes lean and the fuel trims run up — often producing lean codes that look like the primary fault.
- The crankcase loses its depression, and pressure that used to be drawn away now pushes outward on every seal. That is how a disconnected hose becomes a leaking crankshaft seal, which is a far larger repair.
- Oil mist is no longer captured, so it escapes into the engine bay instead of being burnt.
Modern engines detect this deliberately, because a ventilation system left disconnected after other work is common and its emissions consequence is real. The letter identifies which hose, and the vehicle's own documentation maps that to a physical run.
This is often a cheap repair caught early and an expensive one caught late. A hose pushed back on and clipped costs minutes; a crankshaft seal replaced because pressure had nowhere to go does not.
Why this page exists when its neighbours do not. Nothing in the public web documents this block — four independent searches established that on 2026-08-10. This code is written because a manufacturer named it, with its definition, in a technical service bulletin filed with the US road safety regulator, and that OEM wording agrees with the standard's own enumeration. Its neighbours have no such document, so they remain undocumented rather than guessed.
Likely causes
Start here
Less common
- Split or disconnected intake boot · moderate
- Heat damage to sensor or wiring · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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