P0037 on Subaru: How to Diagnose & Fix
HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
1 Subaru model · 1 documented issue · $150-$450 repair
P0037 on Subaru by model: symptoms, diagnosis and fix
Foresters commonly throw front oxygen/air-fuel-ratio sensor heater-circuit codes (P0031 low, P0037 downstream) as the sensors age. The sensors live on the hot exhaust, so the wiring harness near them turns brittle and chafes, and the internal heater element degrades. The result is an illuminated check-engine light, slightly richer/leaner running while the heater is cold, and a guaranteed emissions-test failure. Many owners replace the sensor only to find the real fault is damaged harness wiring at the connector.
Common Symptoms
- Check-engine light with P0031 or P0037
- Failed emissions/smog test
- Slightly reduced fuel economy
- Occasional rough cold running
- No drivability change in some cases (code only)
How to Fix
Scan and confirm the exact code, then inspect the sensor connector and pigtail for melted, chafed or broken wires before condemning the sensor — repair the harness if damaged. If the heater element itself is open, replace the front air/fuel ratio sensor with the OEM-spec part (Subaru sources Denso/NTK); aftermarket universal sensors often re-trigger the code. Clear codes and verify heater operation.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Subaru 22641AA360 Front Air-Fuel Ratio Sensor
replacement only after P0031/upstream heater or sensor testing confirms failure Fitment/availability: 2009-2010 Forester 2.5L naturally aspirated upstream/front position only; confirm VIN and connector Fitment/availability: Add to Cart l…
- Genuine Subaru 22641AA610 Front Air-Fuel Ratio Sensor
replacement only after upstream heater or sensor testing confirms failure Fitment/availability: 2011-2013 Forester 2.5L naturally aspirated upstream/front position; confirm VIN and connector Fitment/availability: direct product page with…
- Genuine Subaru 22641AA670 Front Air-Fuel Ratio Sensor
replacement only after upstream heater or sensor testing confirms failure Fitment/availability: 2014-2016 Forester 2.5L naturally aspirated upstream/front position only; confirm VIN and connector Fitment/availability: ships in 1-3 busine…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
P0037 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0037 mean on a Subaru?
P0037 stands for "HO2S Heater Control Circuit Low (Bank 1 Sensor 2)." The PCM detects low voltage (short to ground or open) in the heater control circuit of the downstream O2 sensor on Bank 1, Sensor 2. On Subaru it is documented across 1 model: Forester.
What are the most common causes of P0037?
The most common causes of P0037 are: Open/short to ground in heater wiring, Failed O2 sensor heater, Corroded connector, Blown fuse. The specific cause varies by vehicle.
How much does it cost to fix P0037 on a Subaru?
Published repair estimates on Subaru range from $150 to $450 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0037 on a different make?
View P0037 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.