P2227 on 2007-2011 Subaru Impreza 2.5i: BARO Sensor and ECM Guide

What's Unique About the 2007-2011 Subaru Impreza

Unlike many vehicles that have an external, easily replaceable BARO sensor, Subaru integrated this sensor directly into the Engine Control Module (ECM) on this generation of Impreza and other models using the EJ253 engine. This design choice means that a P2227 code is not a simple sensor failure, but a failure of a component within the main engine computer itself. As a result, the most common repair is a complete ECM replacement, which is significantly more complex and expensive than a typical sensor swap.

Generation note: This range covers the end of the second generation (2007, GD/GG) and the majority of the third generation (2008-2011, GE/GH/GR/GV). The design of integrating the barometric pressure sensor into the ECM is common across these models with the 2.5i (EJ253) engine.

Symptoms You May Notice

• Check Engine Light is on.
• Reduced engine performance and sluggish acceleration.
• Rough or unstable idle, which may worsen as the engine warms up.
• Decreased fuel economy.
• Engine hesitation or stalling, especially during acceleration or at changing altitudes.

Most Likely Causes

1. Internal Failure of the Engine Control Module (ECM) 🔴 High Probability → Shop Engine Control Module (ECM) The barometric pressure sensor is a non-serviceable component soldered onto the ECM's circuit board. Over time, this internal sensor can fail or drift out of calibration, leading to out-of-range performance and triggering the P2227 code. This is the most widely reported cause in owner forums.
   How to confirm: Use an advanced scan tool to monitor the live data for the BARO sensor. With the Key On, Engine Off (KOEO), the reading should closely match the current local atmospheric pressure (which can be verified with a weather app for your altitude). If the reading is stuck (e.g., at sea level pressure when you are at 5,000 ft) or provides an illogical value, and all wiring is intact, the ECM's internal sensor is faulty.
   Typical fix: There are two main repair paths: 1) Replace the Engine Control Module with a new or remanufactured unit. The replacement ECM must be programmed to the vehicle's VIN and key information. 2) Send the original ECM to a specialized electronics repair service that can diagnose and replace the faulty component on the circuit board. This is often more cost-effective but involves more downtime.
   Est. part cost: $700-$1100 (New OEM), $400-$800 (Remanufactured), $200-$500 (Repair Service)

Rare But Worth Checking

• Wiring Harness or Connector Issue: While far less common than internal ECM failure for this specific code, it's worth checking. A corroded pin or damaged wire at the main ECM connector could theoretically disrupt the circuit, though it's not the typical failure mode.
• Aftermarket ECM/Tuning Calibration Error: If the vehicle has a non-OEM engine control module or has been tuned, it's possible the calibration tables for the barometric pressure sensor are mismatched, causing the ECM to reject otherwise valid sensor data and trigger the code.

Diagnosis Steps

1. Confirm the P2227 code is present using an OBD-II scanner.
2. Use a scan tool capable of viewing live data. Access the Barometric Pressure (BARO) sensor reading (PID).
3. With the Key On, Engine Off (KOEO), compare the BARO sensor reading from the scanner to the actual atmospheric pressure for your location and altitude. A reliable weather app or local weather station data can provide this. For example, at sea level, it should be ~29.9 inHg or ~101 kPa. At 5,000 feet, it should be closer to ~24.9 inHg or ~84 kPa.
4. If the scanner's reading is significantly incorrect (e.g., reading 29.9 inHg when you are in Denver) or stuck at a default value, the sensor is confirmed to be faulty.
5. Since the sensor is internal to the ECM, the next step is a sanity check. Visually inspect the main ECM connectors for any signs of corrosion, moisture, or damage. The ECM is typically located in the passenger footwell, behind the glove box. Clean and reseat the connectors if necessary, then re-check the BARO reading.
6. If the connectors are clean and the sensor reading remains incorrect, the ECM has an internal fault. The next step is to either replace the ECM or send it out for repair.
7. If replacing, ensure the new ECM is the correct part number for the vehicle's VIN, transmission (A/T vs M/T), and emissions standard, and that it is properly programmed to the vehicle.
8. If sending for repair, carefully remove the ECM and ship it to a reputable automotive electronics repair company. Reinstall upon its return.

Parts You'll Likely Need

• Engine Control Module (ECM) (OEM #Varies widely. Examples: 22611AM451 (2007), 22765AB35A (2011 AT PZEV). MUST be verified with VIN.) — This is the most common failure for a P2227 code on this vehicle because the barometric pressure sensor is integrated into it. Part numbers are extremely specific to year, model, transmission, and emissions (Federal or California/PZEV).
  Trusted brands: Subaru (Genuine OEM), Flagship One (Remanufactured), Circuit Board Medics (Repair Service)
  OEM price range: $800-$1200
  Aftermarket price range: $400-$800 (Remanufactured) or $200-$500 (Repair Service)

Platform-Specific Known Issues

• The primary issue for this platform is the integration of the barometric pressure sensor into the ECM, which turns a simple sensor fault into a complex and expensive engine computer replacement or repair.
• Owners on forums frequently express frustration after being advised to replace external MAP or MAF sensors, which does not solve the problem.

Mechanic-Grade Diagnostic Values

• Barometric Pressure (BARO) Live Data PID — expected: Should match local atmospheric pressure at Key On, Engine Off (e.g., ~101 kPa / 29.9 inHg at sea level; ~84 kPa / 24.9 inHg at 5,000 ft).. Failure: Value is stuck, reads an illogical pressure for the altitude, or does not change.
• Internal BARO Sensor Voltage (Theoretical) — expected: A typical, functional external BARO sensor operates within a 0.5V to 4.5V range.. Failure: A voltage outside this range would indicate a fault. However, this is not directly measurable on this vehicle as the sensor is internal to the ECM.

Scan Tool Commands That Help

• Subaru Select Monitor or equivalent professional scanner: Current Data Display > Engine Control System > Atmospheric Pressure — This is the primary diagnostic step to read the live data from the internal barometric pressure sensor to verify if it is rational.
• Subaru Select Monitor or equivalent professional scanner: Immobilizer > Engine Control Module Registration — This function is mandatory after installing a new or used replacement ECM. It pairs the replacement ECM to the vehicle's keys and immobilizer system, allowing the engine to start.

Wiring & Ground Locations

• ECM Main Connectors & Ground — The ECM is located in the passenger-side footwell, typically behind or to the side of the glove compartment.. Since the BARO sensor is internal, its 'circuit' is inside the ECM. A fault could theoretically be caused by a poor power or ground connection to the entire module. Inspecting the main ECM connectors for corrosion or damage is a crucial, though unlikely, final check before condemning the module itself.

Real Owner Repair Stories

• Subaru Impreza Club forum user (2009 Impreza 2.5i non-turbo) — Check Engine Light with code P2227.
  ❌ Tried (didn't work) Checked and cleaned the MAP sensor, Checked and cleaned the MAF sensor, Looked for bad vacuum lines, Reset ECU
  ✅ What actually fixed it The user noted that the official service manual's procedure for P2227 was to replace the ECU, confirming that the BARO sensor is internal and the most likely point of failure is the module itself.

OEM Part Supersession History

• 22611AM450 → 22611AM451 — Revision or update by the manufacturer.
  Heads up: Part numbers are highly specific. Always verify with VIN, transmission type, and emissions standard (Federal vs. PZEV) before ordering.

Model Year Variations Within This Range

• 2007-2011: The most critical variation when replacing the ECM is not just the model year, but the vehicle's specific configuration. The correct ECM part number depends on the transmission (Automatic vs. Manual) and the emissions standard (Federal vs. PZEV/California). An ECM from a car with a different configuration will not work correctly.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Head Gasket Failure (EJ253) 🔴 High — Very common, typically occurs between 80,000 and 150,000 miles. The single overhead cam (SOHC) EJ253 engines in this range are prone to external oil and coolant leaks from the head gaskets.
• Premature Wheel Bearing Failure 🟠 Medium — Commonly reported failure, sometimes as early as 30,000-60,000 miles, though more typical around 100,000 miles. Owners report a humming or grinding noise that changes with vehicle speed. (Ref: Subaru has revised the part design in later years but no widespread recall was issued for this generation.)
• Timing Belt Replacement Interval 🔴 High — This is a critical maintenance item, not a failure, but ignoring it leads to catastrophic engine damage. The service interval is 105,000 miles. It is crucial for owners of used vehicles to verify if and when this service was performed.
• Oil Consumption/Leaks 🟠 Medium — The EJ253 engine is known for oil consumption and leaks from various seals, such as valve covers and the oil pan gasket, as the vehicle ages.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, a used OEM ECM from a reputable recycler is a very common and cost-effective choice, often saving hundreds of dollars compared to a new unit from the dealer.

What to inspect on the donor part:

• Match the OEM part number on your original ECM EXACTLY. Do not use a part that is 'close enough'.
• Verify the donor vehicle had the same engine, transmission (A/T vs M/T), and emissions type (PZEV vs Federal).
• Visually inspect the used ECM for any signs of physical damage, water intrusion, or corrosion on the connector pins.
• Ensure the seller offers a warranty or return policy.

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

• Engine Control Module (ECM). While you can buy used, it should be a genuine OEM part. Unbranded, 'new' aftermarket ECMs are not recommended due to the complexity of vehicle-specific programming and communication protocols.

Aftermarket brands forum-validated for this vehicle:

• For repair services of your existing ECM: Circuit Board Medics, Flagship One.
• For ECM cloning services: Various online providers can perform this service (search 'Subaru ECM cloning').

Brands owners have reported issues with on this vehicle:

• Generic, no-name, or universal engine computers. The ECM must be specific to the Subaru platform.

Real Owner Stories

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

Related OBD-II Codes

• P2229 — Barometric Pressure Sensor 'A' Circuit High. This code was reported by an owner alongside P2227, indicating they are triggered by the same internal ECM sensor failure.
• P0171 — System Too Lean. An incorrect barometric pressure reading causes the ECM to miscalculate air density, leading to an improper air/fuel mixture and potentially triggering fuel trim codes.
• P0172 — System Too Rich. Similar to P0171, a faulty BARO sensor can cause the ECM to command an incorrect fuel mixture, leading to a rich condition and decreased fuel economy.
• P0300 — Random/Multiple Cylinder Misfire Detected. The incorrect air/fuel ratio caused by the faulty BARO sensor can lead to unstable combustion, resulting in the rough idle, hesitation, and stalling symptoms that can trigger a misfire code.
• P0102 — Mass or Volume Air Flow Sensor 'A' Circuit Low. The ECM compares BARO and MAF sensor data. A failed BARO sensor can create a data conflict, potentially flagging the MAF sensor even if it's working correctly. This aligns with owner reports of mistakenly replacing the MAF sensor.

Frequently Asked Questions