P2C91: Crankcase Ventilation System - Hose B Disconnected
The ECM detects that crankcase ventilation hose B is disconnected based on pressure or vacuum signals. Unmetered air ingress and oil mist escape are possible.
What P2C91 means
P2C91 is a generic OBD-II powertrain code in the emissions group.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Not required
Get it fixed
Post this code once and get quotes from local mechanics. Free to post.
Makes the repair and parts links below specific to your car. Kept in this browser only.
Common causes
- 01Hose disconnected at fittingMost likely
- 02Hose split or perforatedPossible
Can I drive with P2C91?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P2C91
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P2C91. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P2C90. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Check live data
Watch the related sensor and actuator readings in live data (Crankcase vent hose B, Crankcase pressure sensor, Intake manifold) and compare them with expected values in the service information for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Hose disconnected at fitting; hose split or perforated. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
P2C91 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Easy
- Good DIY job?
- Yes, with a scan tool
Basic hand tools; a common first DIY job.
Parts and systems involved
- Crankcase vent hose B
- Crankcase pressure sensor
- Intake manifold
P2C91 FAQ
What does P2C91 mean?
P2C91 means “Crankcase Ventilation System - Hose B Disconnected”. The ECM detects that crankcase ventilation hose B is disconnected based on pressure or vacuum signals. Unmetered air ingress and oil mist escape are possible.
Is P2C91 serious? Can I keep driving?
We rate P2C91 as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P2C91?
The most common causes, from most to least likely: Hose disconnected at fitting; Hose split or perforated. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P2C91?
Typical labor is about $25–$125 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P2C91 myself?
DIY difficulty is easy. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will P2C91 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.