P0299 on 2007-2021 Mitsubishi Outlander Diesel: Turbo Underboost Causes and Fixes

What's Unique About the 2007-2021 Mitsubishi Outlander

The Mitsubishi Outlander diesel models in this year range use two different engines: a 2.0L VW-sourced 'DI-D' engine (engine code BSY, 2007-2012) and Mitsubishi's own 2.2L '4N1' engine (engine code 4N14, 2012-2021). While the P0299 code means the same for both, the most common failures are often simple mechanical issues rather than turbo failure. Owners frequently report problems with boost leaks from hardened rubber seals on the charge pipes or, notably, a small port for the boost pressure sensor getting clogged with carbon, leading to a false underboost reading. The boost control solenoid is also a frequent point of failure that can be mechanically faulty even if it tests correctly for electrical resistance.

Generation note: This range covers two Outlander generations. The 2nd Gen (2007-2012) typically used a 2.0L DI-D diesel engine sourced from Volkswagen (engine code BSY). The 3rd Gen (2013-2021) used a 2.2L diesel engine made by Mitsubishi (engine code 4N14). While the causes for P0299 are similar (boost leaks, sensor issues), the exact part numbers for hoses, seals, and sensors will differ between these engines. The 2.0L VW engine is also known for sticky turbo vanes, while the 2.2L Mitsubishi engine is noted for the MAP sensor port clogging.

Symptoms You May Notice

• Significant loss of engine power (Limp Mode).
• Check Engine Light is on.
• Poor acceleration and sluggish performance.
• Engine RPM may be limited (e.g., will not rev over 2000-3000 RPM).
• Hissing, whistling, or whirring sounds from the engine bay, especially under acceleration.
• Visible black smoke from the exhaust under load, indicating a rich condition from a boost leak.

Most Likely Causes

1. Boost Leak from Intercooler Hoses/Seals 🔴 High Probability → Shop Intercooler The rubber seals on the turbo outlet and throttle body inlet pipes are a very common failure point. They harden, wear out, and fail over time, causing pressurized air to leak. Hidden cracks can open up under pressure.
   How to confirm: Visually inspect all charge pipes between the turbo, intercooler, and intake manifold. Look for loose clamps, cracked hoses, or oily residue around connections, which indicates a leak. A smoke test is the most effective method to pinpoint hard-to-see leaks. 🎬 See how to find and fix common intercooler hose leaks
   Typical fix: Replace the worn seals or the entire hose assembly if it is cracked. Ensure all clamps are tight. Owners report success by replacing just the seals on the turbo outlet and throttle body inlet ducts.
   Est. part cost: $20-$120
2. Clogged Boost Pressure (MAP) Sensor Port 🔴 High Probability On the 2.2L 4N14 engine in particular, the small passage in the intake manifold leading to the boost pressure sensor is highly prone to clogging with carbon and soot. This prevents the sensor from reading the actual boost pressure, tricking the ECU into thinking there is an underboost condition even when there isn't one.
   How to confirm: Remove the boost pressure sensor from the intake manifold. Carefully inspect the small port it sits in. Use a small pick, wire, or a small drill bit (turned by hand) to gently probe the hole to see if it is blocked with hard carbon deposits.
   Typical fix: Carefully clean the carbon out of the sensor port using a pick and carburetor cleaner. Also, clean the sensor tip itself if it is oily or sooty. This often resolves the code with no parts required and is a widely recommended first step after checking for obvious leaks. 🎬 Watch: How to clean carbon from the 4N14 intake manifold
   Est. part cost: $0-$15
3. Faulty Turbo Boost Control Solenoid 🟡 Medium Probability The vacuum solenoid that controls the turbo's actuator can fail. Forum users report that it can fail mechanically (getting stuck) while still testing correctly for electrical resistance (e.g., showing 10-14 Ohms). This prevents it from applying the necessary vacuum to the actuator to build boost.
   How to confirm: With the engine running, use a vacuum gauge to check for vacuum at the solenoid and at the turbo actuator. Use a scan tool to command the solenoid on and off to see if it functions and affects the vacuum signal. If the solenoid has vacuum going in but not coming out when commanded, it has failed.
   Typical fix: Replace the boost control solenoid. This is a common fix reported by owners after checking for leaks.
   Est. part cost: $50-$150
4. Sticking Variable Geometry Turbo (VGT) Vanes ⚪ Low Probability Like many diesel engines, carbon buildup from short trips or EGR issues can cause the internal vanes that regulate exhaust flow within the turbo to stick. If they stick in the 'open' position, the turbo cannot build sufficient boost at lower RPMs. This is noted as a particular issue on the 2.0L VW engine.
   How to confirm: Attempt to move the turbo actuator rod by hand (when the engine is off and cool) or with a vacuum pump. It should move smoothly through its full range of motion (approx. 10-15mm). If it is sticky, gritty, or seized, the vanes are likely carboned up.
   Typical fix: Sometimes, a sustained high-speed drive ('Italian tune-up') can help clear the vanes. In other cases, the turbo must be removed for professional cleaning. More often, the entire turbocharger assembly is replaced.
   Est. part cost: $800-$2000

Rare But Worth Checking

• Blocked Air Filter: → Shop Air Cleaner Assembly A severely clogged air filter can starve the turbo of air, preventing it from building boost. Always check this first as it's a simple and cheap fix.
• Cracked Intercooler: → Shop Intercooler Less common than hose leaks, but a crack in the intercooler itself will cause a significant boost leak. A smoke test will reveal this.
• Blocked DPF or Catalytic Converter: → Shop Catalytic Converter A severe restriction in the exhaust system can create backpressure that prevents the turbo from spooling up effectively. This is usually accompanied by other exhaust-related codes like P1498 or P2463.
• Leaking Vacuum Lines: Small vacuum lines controlling the turbo actuator or other components can crack or split, causing a loss of control over the turbo. These leaks can be hard to see.

Diagnosis Steps

1. Read the fault codes with an OBD-II scanner to confirm P0299 is the primary code. Note any other codes like P0106.
2. Perform a thorough visual inspection of the entire air intake system. Start at the air filter box and trace the piping to the turbo, then from the turbo to the intercooler, and finally from the intercooler to the engine's intake manifold. Look for loose clamps, disconnected hoses, cracks, or oily residue which indicates a leak.
3. Specifically for the 2.2L 4N14 engine, remove the Boost Pressure (MAP) sensor from the intake manifold. Inspect the sensor tip and, more importantly, the port it mounts into for heavy carbon buildup. Carefully clean the port with a pick or soft wire.
4. Check the engine air filter to ensure it is not clogged.
5. If no obvious issues are found, perform a smoke test on the intake system to definitively identify any pressure leaks from cracked hoses, seals, or the intercooler.
6. Test the turbocharger's wastegate actuator. For vacuum-operated systems, apply vacuum with a hand pump to see if the actuator rod moves smoothly through its full range of motion. Check all associated vacuum lines for cracks or leaks.
7. Test the boost control solenoid. Confirm it is receiving power and check if it is correctly modulating vacuum to the actuator. Remember that it can fail mechanically even if it passes an electrical resistance test.
8. If all external components check out, the issue may be internal to the turbocharger (sticking VGT vanes or bearing failure), requiring removal for inspection or replacement.

Parts You'll Likely Need

• Intercooler Hose or Seal Kit (OEM #1505A568 (Hose for 2.2L 4N14, 2012-2020), 1505A056 (Hose for 2.0L BSY, 2007-2012)) — The rubber hoses and their integrated seals are a very common failure point, leading to boost leaks that directly cause P0299.
  Trusted brands: Mitsubishi Genuine, Aftermarket hose kits (e.g., from D2P Autoparts)
  OEM price range: $80-$150
  Aftermarket price range: $40-$80
• Boost Pressure Control Solenoid — This solenoid controls the turbo actuator and can fail mechanically, preventing the turbo from building boost. It's a frequent culprit when no leaks are found.
  Trusted brands: Pierburg, Mitsubishi Genuine
  OEM price range: $100-$200
  Aftermarket price range: $50-$120
• Boost Pressure Sensor (MAP Sensor) (OEM #1865A210) — While the sensor itself is often robust, it can fail. More commonly on the 2.2L 4N14, the port it reads from gets clogged, leading to a misdiagnosis of a bad sensor.
  Trusted brands: Mitsubishi Genuine, Denso, Bosch
  OEM price range: $90-$180
  Aftermarket price range: $40-$100

Related Codes That Often Appear With This One

• P0106 - Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem: This code can appear with P0299, especially when the MAP sensor port is clogged, as the sensor gives an erratic or implausible reading.

Platform-Specific Known Issues

• A known issue is the clogging of the small port for the boost pressure (MAP) sensor in the intake manifold with carbon, particularly on the 2.2L 4N14 engine. This is a very common cause of a false P0299 code.
• The seals on the intercooler pipes are a frequent failure item, leading to boost leaks. Owners often replace just the seals or the entire pipe assembly to resolve the issue.
• The vacuum-operated boost control solenoid is known to fail mechanically, getting stuck internally, even when electrical tests show it as functional.

Mechanic-Grade Diagnostic Values

• Boost Pressure (MAP) Sensor Voltage Range — expected: 0.25 V to 4.75 V. Failure: Voltage outside this range, or not changing with engine load.
• Boost Pressure (MAP) Sensor Reading at Idle — expected: Approximately 28-30 kPa. Failure: A reading that is significantly higher or lower, or does not match a reading from a manual vacuum gauge.
• Boost Control Solenoid Resistance — expected: No reliable Ohm value is available for diagnosis.. Failure: A resistance test is not a reliable method for condemning this part. A solenoid can have correct resistance but be mechanically stuck. A functional test using a vacuum pump and applying 12V to check for clicking and vacuum hold/release is the correct procedure.

Scan Tool Commands That Help

• Mitsubishi MUT-III or equivalent professional scan tool: Turbo Actuator Test / VGT System Check — This bidirectional command should be used after confirming no boost leaks. The tool commands the VGT actuator to sweep through its full range of motion. The technician can then observe if the actuator moves smoothly without sticking or binding, which would indicate a problem with the actuator or the internal turbo vanes. Some tools can also read error codes directly from the actuator module and perform calibration after a new actuator is installed.

Wiring & Ground Locations

• ECM Ground — Generally on the engine block. One specific ground point mentioned in service documents is G108 on the cylinder block.. A high-value forum report identified a P0234 (overboost, often related to P0299 causes) as being caused by a poor ECM ground. High paint buildup under the ground connection point on the engine block caused high resistance. Cleaning the paint from the ground point and re-securing the connection resolved the issue. This can cause erratic sensor readings and incorrect turbo control.
• Engine Control Module (ECM) — Typically located behind the driver or passenger side kick panel in the cabin.. If wiring issues are suspected, technicians will need to access the ECM to test for continuity and voltage at the pins corresponding to the MAP sensor, boost control solenoid, and other related components.

Real Owner Repair Stories

• YouTube video by 'DIY Khan' (Mitsubishi Outlander with 2.2L 4N14 Diesel Engine) — Loss of power, blowing smoke.
  ❌ Tried (didn't work) Initial diagnosis pointed towards general power loss issues.
  ✅ What actually fixed it The root cause was a completely blocked MAP sensor port in the intake manifold. The video shows the removal of the intake manifold, revealing it was heavily clogged with carbon. The small passage to the sensor was entirely blocked, preventing it from reading boost. The fix was to thoroughly clean the intake manifold and the sensor port.
• Forum user on Mitsubishi-Forums.com (2009 Outlander 2.0L BSY Diesel) — Limp mode, loss of power, P0234 (overboost) code which has similar root causes to P0299.
  ❌ Tried (didn't work) Living with the problem for years, resetting the light.
  ✅ What actually fixed it The user suspected sticking VGT vanes due to carbon buildup from the EGR system. As a last resort before replacing the turbo, they injected 'Mr. Muscle' oven cleaner foam into the exhaust side of the turbo through the O2 sensor port. After letting it soak and then driving the vehicle, the turbo began functioning correctly again, resolving the limp mode. This confirms that carbon buildup on the VGT mechanism is a real-world cause on the VW-sourced BSY engine.

"I Checked Everything" — The Actual Cause

• If a smoke test is performed and no leaks are found in the charge air system (hoses, intercooler, etc.), this is a critical diagnostic step that strongly points away from a simple boost leak. The P0299 code is now more likely being caused by a component failure rather than a leak. The diagnostic priority should shift to: 1. Clogged MAP Sensor Port (especially on 2.2L 4N14): The system is sealed, but the sensor cannot read the pressure that is present. 2. Faulty Boost Control Solenoid: The solenoid is not commanding the turbo actuator correctly due to an internal mechanical or electrical failure. 3. Sticking VGT Vanes/Actuator: The turbo itself cannot respond to commands to build boost due to internal mechanical binding from carbon or actuator failure. A clean smoke test is not an 'all clear'; it's a sign to look deeper at the control and mechanical side of the turbo system.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• DPF System Blockage and Regeneration Failure 🔴 High — Common for vehicles used primarily for short, low-speed journeys. Can occur at any mileage if regeneration cycles are not completed.
• Automatic/CVT Transmission Failure or Hesitation 🔴 High — Reported across multiple model years, particularly 2014-2018. Symptoms like whining, hesitation, or shuddering can appear. Some sources state the lifespan can be 100,000-150,000 miles. (Ref: Recall for 2019-2022 Outlander Sport for unexpected downshifts (software issue). TSB 20-23-001REV also exists for transmission problems.)
• Power Tailgate Malfunction 🟡 Low — Commonly reported across various model years. Often caused by an accidentally pressed deactivation button in the cabin, not an actual fault.
• Premature Brake Wear 🟠 Medium — Owners of later models (e.g., 2018) have reported needing to replace pads and sometimes rotors earlier than expected, sometimes around 23,000 miles.
• EGR System Clogging 🟠 Medium — Like many modern diesels, the EGR system can become clogged with carbon, leading to performance issues and fault codes.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For major structural components like a replacement intercooler (if the original is cracked) or entire charge pipe assemblies, a used part from a low-mileage donor can be a cost-effective option. Visual inspection for damage is usually sufficient.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For hoses, squeeze the rubber to ensure it is still pliable and not hard or brittle.
• Check for oily residue inside the pipes, as excessive oil may indicate the donor vehicle had severe blow-by or a failing turbo.
• Inspect intercooler fins for excessive damage or corrosion that could impede airflow.

OEM-only on this vehicle (don't cheap out):

• Boost Pressure Sensor (MAP Sensor): Forum reports and general mechanic experience suggest that aftermarket sensors can have a high failure rate or provide inaccurate readings, leading to a repeat diagnosis. A user reported an aftermarket MAP sensor failing in just two months.
• Turbocharger Assembly: While expensive, a new or professionally remanufactured OEM turbocharger is strongly recommended over a used one from a junkyard. The history and internal condition (bearings, seals, vane mechanism) of a used turbo are unknown and it is a high-labor job to replace if the used part is faulty.

Aftermarket brands forum-validated for this vehicle:

• Pierburg: Often the OEM supplier for boost control solenoids, making their branded part a reliable alternative to the dealer part.
• D2P Autoparts: Mentioned by owners as a source for affordable aftermarket intercooler hose kits.

Brands owners have reported issues with on this vehicle:

• Unbranded 'no-name' electronic sensors (like MAP sensors) from online marketplaces. These are frequently cited as having poor quality control and short lifespans.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0106 — Often appears alongside P0299 on the 2.2L engine when carbon buildup in the intake manifold affects the boost pressure sensor's ability to read correctly.

Frequently Asked Questions