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DTC codes / P2Cxx · Hybrid propulsion / P2C91

P2C91Crankcase Ventilation System - Hose B Disconnected

P2C91 indicates that the engine control module has detected a disconnected or open circuit in the crankcase ventilation system hose designated as Hose B. The computer monitors the pressure or flow within the crankcase ventilation system and sets this code when the expected signal from Hose B is missing or out of range, typically due to a physical disconnection or a failed sensor.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaHybrid propulsion

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Rough idle or engine stumbling due to unmetered air entering the crankcase
  • Increased oil consumption or oil seepage from seals because crankcase pressure is not regulated
  • Whistling or hissing noise from the engine bay caused by a disconnected hose
  • Possible lean fuel trim codes or driveability issues if the leak is significant

Common causes, most likely first

  1. Hose B physically disconnected, cracked, or broken
  2. Hose B clogged with oil sludge or carbon deposits
  3. Crankcase ventilation pressure sensor faulty or contaminated
  4. Wiring harness to the sensor or valve damaged (open, short, or corroded connector)
  5. Failed crankcase ventilation valve or diaphragm
  6. Engine vacuum leak elsewhere in the system misreported as Hose B
  7. ECM software issue or internal fault (rare)

How to diagnose and fix it

  1. Inspect Hose B and its connections for looseness, cracks, or disconnection; reconnect or replace as needed
  2. Check for obstructions or sludge buildup in Hose B and clean or replace it
  3. Test the crankcase ventilation pressure sensor with a multimeter and compare readings to specifications
  4. Inspect the wiring and connector at the sensor for damage or corrosion; repair as necessary
  5. Verify the crankcase ventilation valve operates correctly and replace if defective
  6. Perform a smoke test to check for other vacuum leaks in the system
  7. Clear the code and test-drive to confirm the repair; if the code returns, consult factory service information for further diagnostics

Don't overlook the simple hose connection

  • A loose or disconnected Hose B is often the result of recent maintenance work, such as an oil change or air filter replacement, where the hose was accidentally knocked off.
  • The code can be set by a sensor that is reading correctly but is contaminated with oil residue, causing a false signal; cleaning the sensor may resolve the issue without replacement.
  • On some vehicles, the crankcase ventilation system uses a heated hose or a sensor integrated into the valve cover, so a fault in that assembly can mimic a simple hose disconnection.
  • A disconnected Hose B may not cause any driveability symptoms, leading owners to ignore the code, but prolonged operation can lead to seal leaks and increased emissions.
  • Always check for technical service bulletins (TSBs) for the specific vehicle, as some manufacturers have updated hose designs or software calibrations to address this code.

Can I keep driving with P2C91?

It is generally safe to drive short distances to a repair shop, but avoid prolonged driving or heavy loads because a disconnected crankcase ventilation hose can cause oil leaks and increased emissions. If you notice rough running or oil leaks, stop driving and have the vehicle inspected promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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