P0299 on 2020-2025 Buick Encore GX: Turbo Underboost Causes and Fixes

What's Unique About the 2020-2025 Buick Encore GX

The 2020-2025 Encore GX and its platform mate, the Chevrolet Trailblazer, are prone to several specific issues that trigger P0299, as documented by GM's own Technical Service Bulletins (TSBs). These include a vacuum line to the wastegate solenoid being restricted by adhesive from the factory (TSB PIP5978), premature wear of the turbocharger's wastegate linkage causing a rattle (TSB 23-NA-058, superseding PIP5829A), and potential charge air cooler icing in very cold weather (TSB 21-NA-293). GM has also issued software updates to the Engine Control Module to address false P0299 codes (TSB PIP5903).

Symptoms You May Notice

• Check Engine Light illuminated
• "Engine Power is Reduced" message on the driver information center
• Significant loss of acceleration or sluggish performance
• Vehicle enters "limp mode," limiting speed and power
• Hissing or whistling noises from the engine bay, indicating a boost leak
• Rattling noise from the engine compartment on a cold start, which may stop once warm [TSB #PIP5829A]
• Jerking or shuddering during acceleration

Most Likely Causes

1. Worn Turbocharger Wastegate Linkage 🔴 High Probability This is a well-documented failure. TSB 23-NA-058 (which replaces PIP5829A) directly addresses a cold start rattle and P0299 caused by premature wastegate linkage wear. The wear prevents the wastegate from closing fully, allowing boost to leak. A GM technician confirmed this is a common failure requiring turbo replacement, often between 20k-50k miles.
   How to confirm: Listen for a distinct rattle from the turbo area on a cold start. A technician can use a long screwdriver or pry bar to gently touch the wastegate actuator rod; if the noise is dampened or stops, the linkage is worn. [TSB #PIP5829A] TSB 23-NA-058 specifies a physical wear check: if the clearance between the actuator rod link-end and the wastegate arm pin is more than 1.5 mm, the turbo should be replaced.
   Typical fix: The official fix is to replace the entire turbocharger assembly, as the linkage is not serviced separately. GM issued Special Coverage N232407740 for certain 2020 Buick Encore GX vehicles with the 1.2L engine, extending the warranty on the turbocharger to 15 years or 150,000 miles.
   Est. part cost: $800-$1500
2. Restricted Wastegate Solenoid Vacuum Line 🔴 High Probability TSB #PIP5978 specifically calls out that the vacuum supply line from the vacuum pump to the wastegate solenoid can be restricted with adhesive bonding material from the factory. [TSB #PIP5978] This prevents the wastegate from being controlled properly.
   How to confirm: Visually inspect and physically check the vacuum line (GM Part Number 55513554 for the 1.2L) between the vacuum pump and the wastegate solenoid for kinks, blockages, or visible adhesive at the hose ends. [TSB #PIP5978]
   Typical fix: Clear the restriction or replace the affected vacuum hose assembly. TSB PIP5978 advises replacement. [TSB #PIP5978]
   Est. part cost: $20-$50
3. Outdated Engine Control Module (ECM) Calibration 🟡 Medium Probability GM has released software updates to correct logic that could falsely trigger a P0299 code. TSB #PIP5903 explicitly mentions updating the ECM calibrations for this DTC.
   How to confirm: A GM dealership or qualified shop with access to GM's service information system (TIS2Web) must check the vehicle's current calibration ID against the latest available software.
   Typical fix: Reprogram the Engine Control Module with the latest software calibration. This is a dealer-only operation.
   Est. part cost: $0 (parts), $100-$200 (labor)
4. Charge Air Cooler (CAC) Icing ⚪ Low Probability In extremely cold weather (below 0°F / -18°C), condensation can freeze inside the charge air cooler (intercooler), creating a blockage that restricts airflow. TSB #21-NA-293 documents this concern and provides a specific ECM calibration to help mitigate it. This condition can also increase crankcase pressure, potentially causing oil leaks.
   How to confirm: This issue is diagnosed by inspecting the charge air cooler and its plumbing for ice or significant water accumulation, particularly after short trips in sub-freezing temperatures. The issue may resolve itself after the engine warms up fully.
   Typical fix: Thaw and drain the charge air cooler system. Install the updated ECM calibration per TSB 21-NA-293. In some cases, a winter grille cover may be recommended.
   Est. part cost: $0-$100
5. Boost/Vacuum Leak ⚪ Low Probability
   How to confirm: Perform a smoke test on the intake and charge air system to identify leaks from cracked hoses, loose clamps, or a damaged intercooler.
   Typical fix: Repair the source of the leak, which usually involves replacing a hose, tightening a clamp, or replacing the intercooler.
   Est. part cost: $20-$400

Rare But Worth Checking

• Faulty Turbocharger Bypass or Wastegate Solenoid: While the linkage is more common on this platform, the controlling solenoid can also fail electrically or mechanically. A diagnostic scan tool can command the solenoid to operate while a technician checks its function with a vacuum gauge.

Diagnosis Steps

1. Check for Special Coverage: Enter the vehicle's VIN into the GM warranty system to check for Special Coverage N232407740 (for 2020 1.2L models) or other applicable programs.
2. Scan for Codes: Read all stored DTCs to see if codes like P0234, P0236, or P0420 are present, which can guide the diagnosis.
3. Check for TSBs: Review all applicable TSBs, especially 23-NA-058 (wastegate), PIP5978 (vacuum line), 21-NA-293 (CAC icing), and PIP5903 (software).
4. Cold Start Rattle Test: Listen for a rattle from the turbo area on a cold start. If present, perform the wastegate actuator rod touch test as described in TSB PIP5829A to confirm linkage wear.
5. Inspect Vacuum Line: Remove and inspect the vacuum hose between the vacuum pump and wastegate solenoid for adhesive blockages per TSB PIP5978.
6. Check Software Version: If no mechanical faults are found, have a dealer verify the ECM calibration is up to date per TSB PIP5903.
7. Perform Smoke Test: If leaks are suspected, perform a smoke test on the entire intake and charge air system.
8. Monitor Boost Pressure: Use a scan tool to monitor desired vs. actual boost pressure during a test drive to confirm the underboost condition in real-time.
9. Test Solenoids: If other tests are inconclusive, test the wastegate control solenoid and bypass valve for proper electrical and mechanical function using a vacuum gauge and scan tool commands.

Parts You'll Likely Need

• Turbocharger Assembly (OEM #25204082 (for 1.2L LIH per Special Coverage N232407740)) — This is the required fix for the common problem of a worn wastegate linkage, which is integral to the turbo.
  Trusted brands: ACDelco (OEM)
  OEM price range: $1000-$1700
  Aftermarket price range: $700-$1200
• Engine Control Module (ECM) Reprogramming — GM has issued software updates to fix erroneous P0299 codes (TSB PIP5903) and to mitigate CAC icing issues (TSB 21-NA-293). This is a dealer-only labor operation.
  OEM price range: $100-$250 (Labor)
• Turbocharger Wastegate Solenoid Vacuum Hose (OEM #55513554 (for 1.2L LIH per Special Coverage N232407740)) — A specific TSB (PIP5978) mentions this hose can be restricted from the factory, causing an underboost condition.
  Trusted brands: ACDelco (OEM)
  OEM price range: $20-$50
  Aftermarket price range: $10-$30

Related Codes That Often Appear With This One

• P0234 — Turbocharger Overboost Condition. Can appear with P0299 in cases of CAC icing or erratic wastegate control. [TSB #21-NA-293]
• P0236 — Turbocharger Boost Sensor 'A' Circuit Performance. Can be set alongside P0299 if the system is experiencing erratic boost levels due to CAC icing or other issues. [TSB #21-NA-293]
• P0420 — Catalyst System Efficiency Below Threshold. A failing turbo can leak oil into the exhaust, contaminating and destroying the catalytic converter over time.

Technical Service Bulletins (TSBs) & Recalls

• PIE0831A: Initial information gathering from GM regarding P0299.
• PIP5978: Notes the possibility of a restricted vacuum supply line to the wastegate solenoid.
• PIP5903: Recommends updating Engine Control Module calibrations for P0299.
• 21-NA-293: Details issues with charge air cooler icing in extreme cold causing P0299.
• PIP5829A: Addresses P0299 and/or cold start rattle caused by turbocharger wastegate linkage wear.
• N232407740: Special Coverage program for turbocharger failure on some 2020 1.2L models, often related to P0299.

Platform-Specific Known Issues

• TSB #23-NA-058 / PIP5829A: Documents P0299 and/or a cold start rattle caused by premature wear on the turbocharger wastegate linkage. The fix is turbo replacement.
• TSB #PIP5978: A restricted vacuum supply line to the wastegate solenoid due to factory adhesive can cause P0299.
• TSB #21-NA-293: In extreme cold, ice can block the Charge Air Cooler (CAC), causing P0299 and other codes. An ECM update is available to help manage this.
• Special Coverage N232407740: Extends the warranty for turbocharger failure on certain 2020 1.2L Encore GX models to 15 years or 150,000 miles.

Mechanic-Grade Diagnostic Values

• Turbocharger Wastegate Linkage Play — expected: Less than 1.5 mm of clearance between the actuator rod link-end and the arm pin.. Failure: Clearance greater than 1.5 mm or significant ovalization of the arm hole indicates excessive wear requiring turbo replacement.
• Wastegate Regulator Solenoid Vacuum at Idle — expected: Less than -17 kPa (-0.17 bar, 5 in Hg). Failure: If vacuum is -17 kPa or greater at idle, the solenoid valve may be faulty.
• Wastegate Regulator Solenoid Vacuum at >5000 RPM — expected: Greater than -50 kPa (-0.5 bar, 15 in Hg). Failure: If vacuum is less than -50 kPa when commanded by the scan tool, the solenoid valve may be faulty.
• Desired vs. Actual Boost Pressure (Scan Tool Live Data) — expected: Actual boost pressure should closely track desired boost pressure under load.. Failure: A large, persistent gap, such as Desired: 137 kPa vs. Actual: 35 kPa, confirms a significant underboost condition.

Scan Tool Commands That Help

• GDS2 (or equivalent professional scanner): Intake System Learned Values Reset — This procedure is required after replacing the turbocharger or the Engine Control Module (ECM) to allow the system to learn the characteristics of the new components.
• GDS2 (or equivalent professional scanner): Turbocharger Learn / Wastegate Learn — After replacing the turbocharger, this function commands the ECM to cycle the wastegate actuator through its full range of motion to learn the new open and closed positions.
• GDS2 (or equivalent professional scanner): Engine Speed Control — Used during diagnosis of the wastegate solenoid to command engine RPM to over 5000 RPM while a technician measures vacuum with a gauge to verify solenoid function under specific conditions outlined in TSBs.

Wiring & Ground Locations

• G101 (Potential) — A common GM ground point located at the front of the engine on the lower block.. This ground is often responsible for the Engine Control Module (ECM) and Transmission Control Module (TCM). A poor connection could cause erratic sensor readings or control issues, though it's not a primary cause for P0299.
• G103 (Potential) — A common GM ground point, often found on the left frame rail or on the cowl above the brake booster.. A poor connection at G103 has been documented on other GM vehicles to cause widespread communication and voltage issues with various modules, including the ECM.
• Tachometer Signal (for diagnostics) — On the 1.2L engine, this signal can be accessed at the Camshaft Position Sensor connector (black, 3-pin) at pin 3. The wire color is Yellow/Violet.. Provides a reliable engine speed signal for diagnostic purposes if a scan tool is not available or to verify scan tool readings.

Real Owner Repair Stories

• Reddit user Olgingerass, self-identified GM Technician (2023 Buick Encore GX, 26,800 miles) — P0299, "Engine Power is Reduced" message.
  ✅ What actually fixed it The root cause was identified as premature wastegate linkage failure. The wear in the linkage prevents the wastegate from fully closing, causing the underboost condition. The fix is a complete turbocharger replacement. The technician noted this failure is common between 20k-50k miles.
• Reddit user (2022 Buick Encore GX, 64,000 miles) — P0299, engine underboost issue.
  ✅ What actually fixed it The turbo needed to be completely replaced. The user noted that the Encore GX and Chevy Trax are essentially the same vehicle and share this common problem.
• YouTube video comment (Buick Encore (Ecotec Turbo)) — Initial turbo failure, followed by a second turbo failure shortly after replacement.
  ❌ Tried (didn't work) Replacing the turbocharger once.
  ✅ What actually fixed it The second failure was caused by the repair shop reusing the original, clogged turbo oil feed line. The final fix required another new turbo AND a new turbo oil feed line. The user recommends replacing the oil feed line any time the turbo is replaced on these engines.

OEM Part Supersession History

• 55513088, 55514781, 55515879, 55515934 → 25204082 — This is the turbocharger assembly for the 1.2L (LIH) engine. The multiple supersessions suggest revisions were made to the part over time, likely to address the common wastegate linkage wear issue.
  Heads up: When replacing the turbo, using the latest part number (25204082) is critical to ensure you have the most updated design.

Model Year Variations Within This Range

• 2020-2023: For the 1.3L (L3T) engine, a change was made to the Mass Air Flow (MAF) sensor design. If the ECM is replaced, it must be programmed with the correct calibration that matches whether the vehicle has the single-sensor or dual-sensor MAF to avoid setting other DTCs.
• 2024: A specific emission recall (A242435780) was issued for 2024 Encore GX models with the 1.2L engine to reprogram the ECM. The original software could cause improper ignition timing after an Auto Stop/Start event, leading to a rough running engine or engine knock.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Brake Booster Electronic Failure 🔴 High — Affects early model years (2020-2021) and was subject to a safety recall. Caused by contamination in the electronic brake boost system. (Ref: GM Recall A202307260 / NHTSA 20V-603)
• Premature Engine Mount Wear 🟠 Medium — Owners report excessive vibration at idle or clunking noises when shifting, which can be symptomatic of failed motor mounts. This is a general issue not specific to one TSB.
• Electrical Glitches (Infotainment/USB) 🟡 Low — Some owners report issues with USB ports not charging or connecting properly, and general infotainment system bugs.
• Brake System Hard Pedal/Noise 🟠 Medium — Complaints of a hard brake pedal, reduced braking power, and noise have been noted by owners of 2020-2021 models. This is separate from the electronic booster recall but related to overall brake performance. (Ref: Recall A202307262)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific P0299 issue, a used turbocharger is NOT recommended. The primary cause is a known design flaw leading to premature wear of the wastegate linkage, with failures reported as early as 20,000-50,000 miles. A used part from a donor vehicle is highly likely to have the same defect or significant wear.

Donor-vehicle mileage cap: roughly under 10000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Verify the part number is the latest superseded version (25204082 for 1.2L).
• Physically inspect the wastegate actuator arm for any play or looseness. Per TSB 23-NA-058, more than 1.5mm of play indicates failure.
• Inspect turbine blades for any signs of impact, chipping, or scoring.
• Check for excessive shaft play (in/out and side-to-side).

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

• Turbocharger Assembly: Given the multiple OEM part revisions to fix the wastegate issue, an OEM part (specifically the latest part number) is the only way to guarantee you are getting the corrected design. Aftermarket units may not have incorporated these specific revisions.
• ECM Reprogramming: This is a software update that can only be performed by a GM dealer or a shop with a subscription to GM's TIS2Web service.

Brands owners have reported issues with on this vehicle:

• Unbranded or no-name turbochargers from online marketplaces should be avoided due to the high likelihood they are based on the original, flawed design and have poor quality control.

Real Owner Stories

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

Related OBD-II Codes

• P0234 — Mentioned as a related diagnostic code to check for when troubleshooting boost control issues.
• P0236 — A boost sensor circuit performance code that may be stored alongside P0299 during diagnosis.
• P0420 — A catalyst efficiency code that can result from long-term turbocharger or wastegate failure leading to oil consumption or improper combustion.

Frequently Asked Questions