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2020 Civic Si Turbo Lag/Boost Loss - Wastegate Issue?

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Mike T. · rep 0 · May 22, 2:42 AM · 1 replies · solved · Question

Vehicle: 2020 Honda Civic Si

Hey everyone, I've got a 2020 Honda Civic Si with about 40,000 miles on it, and lately, I've been feeling a noticeable drop in power, almost like significant turbo lag or even complete boost loss at times. It's not consistent, but it's definitely there, especially when I try to accelerate hard.

I've also started hearing a slight rattling sound from the engine bay, particularly when I let off the throttle after boosting. I'm wondering if this could be related to the wastegate. I've seen some discussions online about wastegate issues with these 1.5T engines.

Has anyone else experienced this with their Civic Si? What was the culprit, and how did you get it fixed? Any specific things I should tell my mechanic to look for?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:42 AM

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ClearTheCode admin answer:

The symptoms you're describing – power loss, turbo lag, and a rattling sound – are indeed indicative of potential issues with the turbocharger system, particularly the wastegate, on your 2020 Honda Civic Si's 1.5T engine.

  1. Wastegate Actuator/Arm: A common issue is wear or looseness in the wastegate actuator arm or its linkage. This can cause the wastegate to not close properly, leading to boost leaks and a loss of power. The rattling sound you hear could be this loose linkage.
  2. Turbocharger Health: While less common at 40,000 miles, internal wear of the turbocharger itself (e.g., bearing play) can also lead to reduced efficiency and noise. However, the wastegate is a more frequent culprit for these specific symptoms.
  3. Boost Leaks: Check all intercooler piping and connections for any cracks or loose clamps. Even a small leak can significantly impact boost pressure.
  4. Sensor Malfunctions: A faulty MAP (Manifold Absolute Pressure) sensor or O2 sensor could send incorrect readings to the ECU, causing it to limit boost or adjust fuel delivery improperly.

Diagnostics:

  • A check engine light might illuminate, potentially storing codes like:
    • P0299: Turbocharger/Supercharger Underboost Condition
    • P0234: Turbocharger/Supercharger Overboost Condition (less likely with power loss, but possible if wastegate is stuck closed intermittently)
    • P0101: Mass Air Flow (MAF) Circuit Range/Performance Problem
  • A mechanic with a diagnostic scanner can monitor live data for boost pressure, wastegate duty cycle, and sensor readings to pinpoint the exact issue.

When to See a Shop:

  • Immediately: If the power loss is significant, the rattling becomes louder, or a check engine light comes on. Continuing to drive with a malfunctioning turbo system can lead to further damage.
  • A Honda dealership or a performance-oriented independent shop familiar with turbocharged Honda engines will be best equipped to diagnose and repair this. They can perform a smoke test for boost leaks and physically inspect the wastegate assembly.
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