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2017 CT6 3.0TT Reduced Power & Turbo Lag - P0299 Code

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Nicole W. · rep 0 · May 22, 3:57 AM · 1 replies · solved · Question

Vehicle: 2017 Cadillac CT6 Platinum

My 2017 Cadillac CT6 Platinum with the 3.0TT engine has been feeling sluggish lately. I've noticed a significant reduction in power, especially when accelerating from a stop or trying to pass on the highway. There's also a noticeable turbo lag that wasn't there before.

The check engine light came on, and when I scanned it, I got a P0299 code, which points to "Turbocharger/Supercharger Underboost." Has anyone else experienced this with their 3.0TT CT6? What was the fix? I'm hoping it's something simple and not a major turbo replacement.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:57 AM

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ClearTheCode admin answer:

The P0299 code, indicating an underboost condition, is relatively common on turbocharged engines, including the 3.0TT in your 2017 Cadillac CT6. This means the engine's boost pressure is lower than what the Powertrain Control Module (PCM) expects.

Common Causes:

  1. Vacuum Leaks: A leak in the vacuum lines controlling the wastegate actuator can prevent the wastegate from closing properly, leading to low boost.
  2. Wastegate Actuator/Solenoid Failure: The actuator itself or its control solenoid can fail, causing the wastegate to remain partially open.
  3. Charge Air Cooler (Intercooler) Leaks: Leaks in the intercooler or its piping can allow boost pressure to escape.
  4. Diverter Valve/Bypass Valve Issues: A faulty diverter valve (also known as a bypass valve) can fail to hold pressure, venting boost prematurely.
  5. Turbocharger Failure: While less common, a failing turbocharger (e.g., worn bearings, damaged compressor wheel) can also cause underboost.
  6. Boost Pressure Sensor Malfunction: A faulty sensor might report incorrect boost levels, though this usually comes with other diagnostic codes.

When to See a Shop:

It's crucial to have this diagnosed by a qualified technician as soon as possible. Continuing to drive with an underboost condition can lead to:

  • Further engine performance degradation.
  • Increased fuel consumption.
  • Potential damage to other engine components if the underlying cause is severe.

A shop will typically perform a smoke test to check for leaks, inspect the wastegate operation, and monitor boost pressure with a diagnostic scanner to pinpoint the exact cause. Early diagnosis can prevent more costly repairs down the line.

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