Turbo Underboost (P0299) & Loss of Power on 2020 Buick Encore GX – Real Diagnostic Story from PROFIX in Norman
A 2020 Buick Encore GX came to PROFIX Auto Repair in Norman with loss of power on startup and a P0299 underboost code. See how our technicians diagnosed a worn wastegate linkage, why a full turbo replacement was needed, and how we got the vehicle back to full power.
When a 2020 Buick Encore GX loses power right after starting and sets a P0299 turbo underboost code, it’s rarely as simple as “the turbo is bad.”
At PROFIX Auto Repair in Norman, we dig deeper with proper diagnostics—even when multiple codes and a recent repair are already involved.
Customer Concern
A customer brought in their 2020 Buick Encore GX with loss of power. The check engine light was on and the vehicle wasn’t delivering the performance it should.
Thorough Diagnosis Revealed the Real Problem
Our technician started by scanning for codes and found several present, including P0102 (mass air flow sensor circuit), communication codes with the MAF sensor, and issues related to the engine control module and DC/DC converter.
Following GM service bulletin #22-NA-008 (which addresses broken ground or data wires commonly causing these exact codes), we located and repaired a broken wire. The codes cleared and the vehicle seemed fine - at first.
We then took it for a test drive. After about 7 miles, the P0299 turbocharger underboost code returned. Live data showed the turbo was trying to make boost, but something wasn’t right.
We followed GM’s diagnostic procedure for P0299 step-by-step:
- Confirmed the MAP sensor and boost pressure sensor were reading correctly with key on/engine off.
- Commanded the wastegate solenoid on and off—it was clicking and functioning.
- Performed a smoke test on the charge pipes and intake—no leaks.
- Did a vacuum test on the wastegate actuator.
That’s when we found the real issue.
The Root Cause: Worn Wastegate Linkage
The wastegate linkage inside the turbo had excessive play and was loose. On these GM 1.2L turbo engines, a worn wastegate doesn’t close fully under boost. This creates an exhaust leak that lets boost pressure escape instead of going into the engine—exactly what triggers P0299 and the power loss the customer felt.
We also found a decent amount of oil in the turbo inlet pipe and noted the engine was low on oil—both common secondary effects of an internal turbo issue. There was even a noticeable rattle on cold start, which is classic for wastegate linkage problems.
Here’s a quick video our technician recorded showing the excessive play in the wastegate linkage:
The Result
The Encore GX is now back to full power with no underboost issues or check engine light. The customer got a lasting repair instead of temporary symptom chasing.
Key Takeaways
- P0299 underboost is often caused by wastegate problems rather than complete turbo failure.
- Multiple codes (especially wiring/MAF communication issues) can mask or coexist with turbo problems—always perform complete diagnostics.
- On modern GM 1.2L/1.3L turbo engines, the wastegate linkage is internal; when it wears, full turbo assembly replacement is usually required.
- Proper testing (vacuum, solenoid command, visual play check, and live data) saves time and money long-term.
- Regular oil changes and addressing low oil levels promptly help protect turbos.
If your Buick Encore GX, Trax, or other GM 1.2L/1.3L turbo vehicle is showing loss of power, a check engine light, or a P0299 code, bring it to PROFIX before it gets worse. These issues rarely fix themselves and can lead to bigger (and more expensive) problems.
We proudly serve Norman and the surrounding Cleveland County area at both of our locations:
PROFIX Auto Repair – West
1121 Rambling Oaks Dr
Norman, OK 73072
📞 (405) 310-2279
🕒 Monday–Friday: 7:30 AM – 5:00 PM
Leon’s PROFIX Auto Repair – East
521 N Porter Ave
Norman, OK 73071
📞 (405) 364-2799
🕒 Monday–Friday: 7:30 AM – 5:00 PM
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