The 2021 Mitsubishi Eclipse Cross's 1.5L turbocharged engine delivers peppy performance when the boost system is sealed and working properly. A P0299 code—Turbo/Supercharger Underboost Condition—indicates the engine isn't reaching expected boost pressure. This results in noticeably reduced power and often traces to a boost leak somewhere in the pressurized intake tract.
Symptoms of Turbo Boost Leak
- Check engine light with P0299 code
- Noticeable loss of power, especially at higher RPM
- Hissing or whooshing sound during acceleration
- Turbo not building boost as expected
- Possible black smoke from exhaust (rich condition from boost compensation)
- Engine may feel sluggish or unresponsive
- Poor fuel economy
Understanding Turbo Boost Systems
The turbocharger compresses intake air, which travels through the intercooler to cool it, then into the intake manifold. This entire pathway—from turbo outlet to intake valves—must be sealed to maintain boost pressure. Any leak allows compressed air to escape, reducing the pressure reaching the cylinders.
Common Boost Leak Locations in the Eclipse Cross
Intercooler Connections
The hot side (from turbo) and cold side (to intake) intercooler pipes use silicone couplings with clamps. These can loosen, crack, or blow off under boost pressure.
Solutions:
- Inspect all intercooler pipe connections
- Tighten loose clamps
- Replace cracked or damaged couplings
Charge Pipe Damage
The plastic or metal charge pipes connecting components can crack, especially if subjected to heat damage or impacts.
Solutions:
- Inspect pipes for cracks or damage
- Replace damaged sections
- Consider upgraded metal pipes if plastic fails repeatedly
Turbo Inlet Hose
The hose between the air filter box and turbo inlet can develop cracks, allowing unmetered air to enter before compression.
Solution: Inspect and replace if damaged.
Intercooler Core Damage
The intercooler itself can develop leaks from corrosion, impact damage, or manufacturing defects.
Solutions:
- Pressure test the intercooler
- Replace if leaking internally
Boost Control Solenoid
The wastegate control solenoid regulates boost pressure. Failures can cause underboost or overboost conditions.
Solution: Test and replace solenoid if faulty.
Wastegate Issues
A stuck-open wastegate allows exhaust to bypass the turbo, reducing boost capability.
Solution: Inspect wastegate operation and actuator.
Finding Boost Leaks
Visual Inspection
Start by visually checking all visible boost pipe connections and hoses for obvious damage, disconnection, or loose clamps.
Pressure Testing
The most reliable method is pressurizing the intake system (with engine off) using shop air or a dedicated boost leak tester. Listen for escaping air and check connections with soapy water.
Smoke Testing
A smoke machine can reveal leaks by making escaping air visible, even in hard-to-see locations.
Diagnosis Steps
- Scan for codes: Confirm P0299 and check for additional codes
- Visual inspection: Check all visible boost components
- Listen for leaks: Hissing during acceleration indicates escaping boost
- Check boost pressure: Compare actual boost to expected values
- Pressure/smoke test: Professionally test for hidden leaks
- Inspect turbo: Check for shaft play or damage
Repair Costs
- Intercooler coupler/clamp: $30-$100
- Charge pipe replacement: $150-$400
- Turbo inlet hose: $50-$150
- Intercooler replacement: $400-$800
- Boost solenoid: $100-$250
- Turbocharger replacement: $1,500-$3,000
- Boost leak diagnosis: $100-$200
The 2021 Eclipse Cross is covered by Mitsubishi's 5-year/60,000-mile warranty. Turbo system components should be covered for defects within this period.