P2227 on 2018-2024 GMC Terrain: Causes and Fixes for BARO Sensor Issues

What's Unique About the 2018-2024 Gmc TERRAIN

For the 2018-2024 GMC Terrain, particularly those with the 1.5L (RPO LYX) and 2.0L (RPO LTG) turbocharged engines, the P2227 code is strongly linked to a specific design issue. Moisture, from either high humidity or the PCV system, can accumulate inside the charge air cooler (CAC). In cold weather (consistently below 20°F/-7°C), this moisture can freeze, restricting airflow and causing erratic pressure readings that trigger the P2227 code, often alongside P0299 (Turbo Underboost) or P0300 (Random Misfire). General Motors has issued multiple, evolving versions of Technical Service Bulletin (TSB) #18-NA-020 acknowledging this exact problem and providing a complex diagnostic tree based on build date and climate.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• "Engine Power Reduced" message on the driver information center
• Reduced engine power or sluggish acceleration
• Rough or erratic idle
• Increased fuel consumption
• Engine hesitation or stalling, especially on heavy acceleration after a long drive in humid conditions.

Most Likely Causes

1. Moisture Buildup / Icing in Charge Air Cooler (CAC) 🔴 High Probability As documented in multiple revisions of GM TSB #18-NA-020, these vehicles are susceptible to moisture from high humidity or the PCV system collecting in the CAC. In cold weather, this can freeze and create a blockage, restricting airflow and leading to incorrect pressure readings. The TSB outlines different fixes depending on the vehicle's build date; for example, vehicles built before March 1, 2018, often require a replacement CAC.
   How to confirm: Inspect the inside of the charge air cooler and its ducts for moisture, ice (in cold weather), or a milky, oily residue. This often requires removing the lower air duct. The presence of other codes like P0299 or P0300 is a very strong indicator.
   Typical fix: Follow TSB #18-NA-020. For vehicles built before certain dates (e.g., March 2018), the fix is to replace the charge air cooler with an updated, wider part. For later models or repeat issues, the TSB may recommend cleaning the existing CAC, installing a lower grill shutter or cover to reduce cold air exposure, and/or reprogramming the ECM.
   Est. part cost: $200-$450
2. Faulty Barometric Pressure (BARO) / MAP Sensor 🟡 Medium Probability On these engines, the BARO function is integrated into one of the pressure sensors (e.g., the boost pressure sensor on the intake pipe or the MAP sensor on the intake manifold). These sensors can become contaminated by the oily moisture coming from the CAC, leading to failure. They can also fail on their own, though it's less common than the CAC issue.
   How to confirm: Use a scan tool to monitor the BARO/MAP sensor's live data with the key on, engine off. The reading should match the atmospheric pressure for your altitude. Compare it to a known good vehicle or weather service data. Also, inspect the sensor tip for oil or moisture contamination after removal. The TSB specifically advises cleaning the boost sensor on 2.0L engines.
   Typical fix: Replace the contaminated or failed MAP/BARO sensor. It is critical to address the source of contamination (the CAC) first, otherwise the new sensor will likely fail again. Clean the connector before installing the new part.
   Est. part cost: $40-$100
3. Wiring or Connector Issue ⚪ Low Probability
   How to confirm: Visually inspect the wiring harness and connector for the relevant MAP/BARO sensor. Look for corrosion, bent pins, or chafed wires, especially near the front of the engine bay where damage could occur. Use a multimeter to check for proper voltage, ground, and signal integrity at the connector.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the connector.
   Est. part cost: $10-$50

Rare But Worth Checking

• Clogged Catalytic Converter: A severely clogged catalytic converter can create excessive backpressure, skewing the readings of various pressure sensors and potentially triggering a P2227 code. This is often a downstream effect of other engine problems and is usually accompanied by other codes. One owner of a 2019 Equinox with P0299 reported the ultimate fix was a new catalytic converter.
• Faulty Powertrain Control Module (PCM): This is very rare. The PCM should only be considered after all other possibilities, including the TSB-related CAC issue, sensor failure, and wiring problems, have been exhaustively ruled out.

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs). For this vehicle and code, TSB #18-NA-020 is the most important first step. Note the vehicle's build date to follow the correct diagnostic path in the bulletin.
2. Scan for other codes. The presence of P0299 or P0300 strongly points to the charge air cooler issue.
3. Inspect the Charge Air Cooler (CAC) system. Disconnect the lower air duct from the CAC and check for any signs of water, ice, or an oily, milky residue. Even a small amount can cause this issue.
4. Inspect the BARO/MAP sensor(s). Remove the sensor(s) and check the tip for oil or moisture contamination. The TSB specifically calls out cleaning the boost sensor on 2.0L engines.
5. Analyze live sensor data. Use an OBD-II scanner to view the BARO pressure reading with the key on and engine off. Compare this reading to the known atmospheric pressure at your elevation to see if it's plausible.
6. Perform a smoke test. The TSB recommends a smoke test of the entire charge air system (from turbo to throttle body) to check for leaks, which would also cause incorrect pressure readings.
7. Inspect wiring. If the sensor reads incorrectly and is not contaminated, check its connector and wiring for damage, corrosion, or looseness.

Parts You'll Likely Need

• Charge Air Cooler (OEM #85046823) — This is the most common failure point leading to code P2227 on this specific vehicle, as documented by GM's own service bulletins. The original design is prone to moisture collection.
  Trusted brands: ACDelco (GM Genuine), Spectra Premium
  OEM price range: $300-$450
  Aftermarket price range: $200-$350
• Manifold Absolute Pressure (MAP) Sensor — This sensor, which includes the BARO function, can fail on its own or become contaminated by the moisture from a faulty charge air cooler. A Reddit user with a 2019 Equinox and codes P2227/P0299 reported the fix was a bad MAP sensor.
  Trusted brands: ACDelco, Bosch, Delphi
  OEM price range: $60-$120
  Aftermarket price range: $40-$80

Related Codes That Often Appear With This One

• P0299 — This code for 'Turbocharger/Supercharger Underboost' is often triggered when a frozen or moisture-filled charge air cooler restricts airflow, preventing the turbo from building the expected amount of boost.
• P0300 — This code for 'Random/Multiple Cylinder Misfire' can occur when a sudden gulp of water that has pooled in the charge air cooler is drawn into the engine during acceleration.
• P0234 — This code for 'Turbocharger/Supercharger Overboost' is also mentioned in later versions of TSB 18-NA-020, suggesting that erratic pressure fluctuations from the CAC issue can also cause overboost spikes.

Technical Service Bulletins (TSBs) & Recalls

• 18-NA-020: Malfunction Indicator Lamp Illuminated with DTC P0300 and/or P0299/P2227 Set. This bulletin, in its many versions, confirms that moisture buildup in the charge air cooler is a known cause for these codes and provides a detailed, evolving set of diagnostic and repair procedures based on build date and climate.

Platform-Specific Known Issues

• GM Technical Service Bulletin #18-NA-020 has been revised numerous times (e.g., Feb 2019, Apr 2020, Mar 2021, Jan 2023), indicating the complexity of the issue. Early fixes focused on replacing the CAC on vehicles built before March 2018. Later revisions added procedures for installing grill shutters/covers in cold climates and ECM reprogramming for 1.5L engines to change shift patterns and reduce the likelihood of freezing.

Mechanic-Grade Diagnostic Values

• MAP/BARO Sensor 5V Reference Voltage — expected: Approximately 5.0 Volts. Failure: Voltage significantly lower than 5.0V indicates a wiring or ECM issue.
• MAP/BARO Sensor Signal Voltage (Key On, Engine Off) — expected: Approximately 4.5 - 5.0 Volts, corresponding to atmospheric pressure.. Failure: Voltage outside the typical 0.5V - 4.5V operating range.
• MAP/BARO Sensor Signal Voltage (Engine Idling) — expected: Voltage should drop to approximately 1.0 - 1.5 Volts due to engine vacuum.. Failure: Voltage does not drop significantly after starting the engine, or remains steady regardless of engine load.
• MAP/BARO Sensor Ground Circuit Voltage — expected: Less than 100 millivolts (0.1V). Failure: Voltage higher than 0.1V indicates a poor ground connection, which can skew sensor readings.

Scan Tool Commands That Help

• GDS2 (GM Dealer Tool): ECM Reprogramming / Software Calibration Update — For 1.5L (LYX) engines, a specific calibration update is available to change transmission shift patterns in cold weather, reducing the chance of CAC icing. This is a key step in the latest version of TSB 18-NA-020.
• GDS2 or equivalent professional scan tool: Clear DTCs — Required after performing repairs to turn off the check engine light and reset the system's fault status.

Wiring & Ground Locations

• MAP Sensor Connector — The MAP (Manifold Absolute Pressure) sensor, which incorporates the BARO function, is typically located on the intake manifold, near the throttle body. On the related Chevy Equinox, it is easily accessible on the front of the intake manifold.. The connector and its wiring are the primary interface between the sensor and the ECM. Corrosion, bent pins, or harness damage can cause the range/performance fault. The TSB for the 2.0L engine specifically calls for cleaning the boost pressure sensor, which is similarly exposed.

Real Owner Repair Stories

• Reddit user B_randen (2019 Chevrolet Equinox AWD 1.5L with 167,000 miles) — Check Engine Light with codes P0299 and P2227, 'Engine Power Reduced' message, and significantly limited power when going uphill, especially in very cold weather.
  ❌ Tried (didn't work) The user first sought advice before attempting repairs.
  ✅ What actually fixed it The final update posted by the owner was simply: 'Update: it was a bad MAP sensor.'

"I Checked Everything" — The Actual Cause

• Multiple versions of GM's TSB #18-NA-020 explicitly state that if a smoke test of the charge air system finds NO leaks, but codes P2227, P0299, and/or P0300 are present, the technician should NOT assume the system is fine. Instead, the TSB directs them to proceed with replacing the charge air cooler (on vehicles built before a specific date) or perform other procedures like installing grill covers or reprogramming the ECM. This indicates that a leak-free system can still be the source of the problem due to internal moisture or icing.

OEM Part Supersession History

• 23270538, 84454110, 85163204, 87830393, 87863765 → 85046823 — The original Charge Air Cooler (CAC) design was prone to moisture accumulation. The updated part is a newly designed, wider cooler intended to mitigate this issue.
  Heads up: The newly designed charge air cooler (85046823) is wider and is NOT compatible with the original lower air baffle on the vehicle. The baffle must also be replaced to accommodate the larger cooler.

Model Year Variations Within This Range

• 2018 models built on or before March 1, 2018: Per early versions of TSB 18-NA-020, if codes P2227/P0299 are present and no leaks are found, the default procedure is to replace the charge air cooler with the updated part.
• 2018-2019 models built on or before January 5, 2019: A later TSB revision extended the build date cutoff for mandatory charge air cooler replacement.
• 2018+ (especially 1.5L LYX engine): The latest TSB versions (e.g., Jan 2023) have shifted strategy. CAC replacement is now only mandated for pre-March 2018 builds that haven't already had it replaced. For the 1.5L engine, a new ECM calibration is recommended to alter transmission shift patterns at highway speeds in cold weather, reducing the potential for ice buildup. This software fix is now a primary countermeasure.
• All years in cold climates: For conditions where icing occurs, later TSBs introduced the option of installing a lower grill shutter or cover to reduce the CAC's exposure to cold air, a procedure not mentioned in the earliest bulletins.