Fix P2279: Mechanic’s solutions that WORKED

The P2279: Intake Air System Leak indicates a fault in the vehicle’s intake air system, specifically pointing out an air leak. This leak allows unmetered air to enter the engine, disrupting the air-fuel mixture and potentially causing issues such as rough idling, stalling, and reduced fuel efficiency. It’s a critical error that should be addressed to ensure the vehicle runs smoothly and maintains optimal performance.

P2279 quick overview

Meaning	P2279: Intake Air System Leak
Is it serious?	This code is serious as it indicates a significant air leak in the intake system, which can affect the engine’s performance and efficiency.
Possible causes	– Cracked or disconnected vacuum hoses – Leaks in the intake manifold gasket – Faulty PCV valve or system – Issues with the crankcase ventilation system – Damaged intake air ducts – Malfunctioning mass airflow sensor
How to diagnose?	Perform Smoke Test: Use a smoke machine to identify any leaks in the intake system. Inspect Vacuum Hoses: Check for cracks or disconnections in the vacuum hoses. Examine Intake Manifold Gasket: Look for signs of wear or damage in the intake manifold gasket. Check PCV Valve/System: Evaluate the PCV valve and system for blockages or malfunctions. Inspect Intake Air Ducts: Look for damage or leaks in the intake air ducts. Test Mass Airflow Sensor: Assess the functioning of the mass airflow sensor.

How to fix P2279 – learn from mechanics

I looked into P2279 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Honda

Vehicle Information: 2005 Honda CR-V LX 2.4L

Issue + Repair History:

• P2279 code returned after 2 weeks.
• No issues with start, idle, run, or drive.
• Checked IAC, brake booster, evap solenoid.
• Problem began after starter and PCV replacement.
• Replaced intake gasket, PCV valve, hose, and some vacuum hoses.
• P1077 fixed by replacing IMRC valve and solenoid.
• P2279 returned, sealed intake and added PCV hose restrictor.
• Discovered engine is from a 2003 CR-V, unknown actual mileage.
• Exhaust cam worn but not replaced.

Other OBD2 Codes + Test Results:

• P2279: Intake Air System Leak

Suggestions to Fix Issue:

• Inspect air bypass thermal valve on the throttle body.
• Change the evap solenoid if leaking vacuum when closed.
• Check if Permatex sealant dissolved by blow-by.
• Use smoke machine to check for leaks.
• Ensure IMRC valve is positioned correctly and sensor is OEM.
• Check the valve with two hoses on driver side (possibly related to idle control).

Final Fix:

• Cleared throttle plate position memory, resolving P2279.
• Left thermal valve blocked as it doesn’t affect operation and isn’t monitored by the computer.
• Adjusted tight intake and exhaust valves.
• Kept old CANP solenoid as replacement leaked more.

Case #2: Honda

Vehicle Information: 2005 Honda Accord SE 3.0L

Issue + Repair History:

• Code P2279: air intake system leaking.
• Checked cam timing; cam and crank timed correctly.
• Performed vacuum leak test with smoke machine; no leaks found.
• Adjusted valve clearance while engine was cold.
• Performed idle relearn procedure manually.
• Code cleared, but returned after a few miles.
• Previous shop replaced timing belt.

Other OBD2 Codes + Test Results:

• P2279: Air intake system leaking.

Suggestions to Fix Issue:

• Check the diagnostic chart for Code P2279.
• Inspect for air leaks between the air filter box and throttle body.
• Look for cracks/holes in duct, filter box, loose clamps, dirty/failed MAF.
• Check the brake booster for leaks.
• Consider the possibility of a sensor problem, such as IAT.
• Check and possibly replace the PCV valve.
• If equipped with a mass airflow sensor, clean it.
• Relearn the electric throttle-by-wire with the HDS scantool if the throttle body was previously cleaned.

Final Fix:

• The issue was traced to an engine problem.
• Cylinder pressure testing revealed a slight leak in cylinder number 5.
• This issue caused rough idling and affected the MAP reading, leading to the P2279 code.
• The vehicle had a history of a broken timing belt after replacement, and the cylinder heads were removed but not fully serviced.

Case #3: Mercedes

Vehicle Information: 2015 Mercedes-Benz C300 2.0L

Issue + Repair History:

• Car runs well for 2-3 minutes, then MIL flashes and stays on.
• Multiple misfire codes and P2279 code indicating a vacuum leak.
• No external vacuum leaks found.
• Previous shop replaced fuel injectors.
• Engine sounds noisy despite regular oil changes with Liqui Moly.
• Questioned possible crankcase ventilation system issue.

Other OBD2 Codes + Test Results:

• P2279: Vacuum leak.

Suggestions to Fix Issue:

• Check injector coding due to injector replacement history.
• Examine PCV system, particularly for sticking check valve in the vent line.
• Perform vacuum testing on the PCV system.
• Inspect the induction system for the turbo, specifically for any broken ventilation hoses.

Final Fix:

• Contacted previous shop: PCV/Oil Separator and injectors were replaced and coded.
• Engine had severe noise from the front and was 2.5 qts low on oil.
• Leak down and compression test showed Cylinder #1 failure.
• Borescope revealed severe scarring on cylinder wall, metal found in oil.
• ECM may have misinterpreted data as an air intake leak.

Case #4: Audi

Vehicle Information: 2006 Audi A4 2.0L Turbo Auto Trans

Issue + Repair History:

• MIL on with codes P0507, P2187, P2279.
• TSB suggested replacing crankcase vent system pressure valve and hose.
• Replaced valve and hose, but CEL returned with same codes after a mile.
• Checked for vacuum leaks but found none.
• Questioned if the valve could be defective.

Other OBD2 Codes + Test Results:

• P0507: Idle high.
• P2187: Bank1 lean.
• P2279: Leak in intake.

Suggestions to Fix Issue:

• Consider using parts directly from the dealer.
• Check if the scanner properly cleared the codes.
• If idle is high and O2 sensors lean, inspect the IAC and tap on it to see if the idle comes down.

Final Fix:

• Installed an updated crankcase vent valve from Audi.
• Cleared codes, test drove for 10 miles, and the light stayed off.
• Returned the vehicle to the owner; issue resolved.

Case #5: Land Rover

Vehicle Information: 2011 Land Rover Range Rover Sport HSE 5.0L

Issue + Repair History:

• Stalls after warming up at idle every 3-5 minutes, restarts immediately.
• Initially had codes P0087 and P2279.
• Replaced both high-pressure pumps, resolving P0087.
• Replaced right valve cover to replace oil separator, resolving P2279.
• Tried new crank sensor, issue persisted.
• No current codes, but still stalls when warm.

Other OBD2 Codes + Test Results:

• Now normal.

Suggestions to Fix Issue:

• Check if supply side fuel pressure is maintained.
• Determine what is lost during stall: low side pressure, spark, or both.
• Scope cam and crank sensors during stalling.
• Check if stalling is due to too low base idle.
• Inspect intake air hoses for cracks post-MAF and consider throttle body service.
• Check supply pump pressure to ensure it isn’t cutting out.
• Scope Autologic scan data for detailed analysis.

Final Fix:

• Issue turned out to be a low fuel pressure sensor problem.
• Replaced the low fuel pressure sensor, resolving the stalling issue.

Advice	Brief Description of Diagnostic Step
Perform Smoke Test	Conduct a smoke test to locate any vacuum leaks in the intake system.
Check PCV System	Inspect the Positive Crankcase Ventilation (PCV) system for faults or blockages.
Inspect Intake Manifold	Examine the intake manifold for leaks or damage.
Evaluate Fuel System	Assess fuel injectors, pressure pumps, and related components.
Check Engine’s Air Induction System	Inspect air filters, hoses, and connections for leaks or obstructions.
Monitor Sensor Data	Use diagnostic tools to monitor readings from relevant sensors.
Inspect Crankcase Vent Valve and Hose	Check the condition and functionality of the crankcase vent valve and hose.
Verify Throttle Body Function	Assess the throttle body for proper operation and cleanliness.
Analyze Engine Compression	Perform a compression test to identify any cylinder-specific issues.
Reset and Recalibrate Systems	After repairs, reset and recalibrate systems such as the idle control.