HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
The P0037 code means the vehicle's onboard diagnostic system has detected: HO2S Heater Control Circuit Low (Bank 1 Sensor 2). This is a low severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $80 - $300 (O2 sensor $60-$200; labor $50-$150)
Best-selling code reader on Amazon. Reads and clears check engine codes on any 1996+ vehicle. Under $30.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Essential for diagnosing sensor codes, checking voltage, and testing circuits. Under $15 and pays for itself on the first job.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light on
- Slightly reduced fuel economy
- Delayed catalytic converter monitoring readiness
- No significant drivability symptoms
- May fail emissions inspection
Probable Causes (Ranked by Likelihood)
- Open heater element in the downstream O2 sensor Very High
- Blown O2 sensor heater fuse High
- Broken or disconnected wire in the heater circuit Moderate
- Corroded or damaged sensor connector Moderate
- PCM ground circuit fault Low
Step-by-Step Diagnostic Procedure
-
Check and replace the O2 heater fuse if blown. If it blows again, check for a short in the circuit.
-
Disconnect the bank 1 sensor 2 O2 sensor and measure heater resistance (2-15 ohms typical). Infinite resistance means the heater element is open.
-
Verify battery voltage is present at the heater power pin with key on, engine off.
-
Check the ground circuit from the sensor connector to a known engine ground. Should read near 0 ohms.
-
Inspect wiring for breaks or heat damage, especially where the harness passes near the exhaust system or under the vehicle.
Common Fixes by Vehicle
What techs usually find when diagnosing P0037 on specific vehicles — tap your vehicle for the fix and the exact part:
2000-2015 Toyota Tacoma/Tundra/4Runner 2.7L/4.0L Easy DIY
Downstream (post-cat) O2 sensor on bank 1 heater resistance drops due to exhaust moisture corroding the heater filament. Replace with a Denso direct-fit sensor. Inspect the upstream exhaust for leaks — leaking manifold gaskets shove raw exhaust over the downstream sensor and kill heaters prematurely.
Labor: 30-45 min2005-2014 GM 5.3L/6.0L (Silverado, Tahoe, Suburban, Sierra) Easy DIY
Post-cat O2 on bank 1 heater circuit fails after exhaust manifold bolts break or manifold develops hairline cracks — moisture enters the sensor body and shorts the heater. Replace the sensor AND repair manifold leaks. Use AC Delco or Denso sensors; universal-fit sensors often fail again within 20K.
Labor: 30-45 min2007-2014 Ford F-150 5.4L 3-Valve Easy (sensor), Advanced (studs) DIY
Downstream O2 sensor heater fails due to broken exhaust manifold studs allowing exhaust leak at the sensor location. Replace the sensor with Motorcraft unit and address manifold stud breakage — a known 5.4L 3V issue. Stud extraction usually requires manifold removal.
Labor: 30 min (sensor), 4-6 hr (studs)Frequently Asked Questions
Can I drive with code P0037?
Yes, you can drive normally. The downstream O2 sensor heater failure will not affect engine performance or drivability. It only delays the sensor from reaching operating temperature, which affects emissions monitoring.
What does low circuit mean for P0037?
Low circuit indicates the PCM detected insufficient current flowing through the heater circuit. This usually means an open circuit -- the heater element burned out, a wire is broken, or the fuse is blown.
How long can I drive with P0037 before fixing it?
You can drive indefinitely without engine damage, but you will fail emissions testing with an active Check Engine Light. Fix it before your next emissions inspection. The only impact is slightly reduced fuel efficiency during cold starts.
Sources
This page is built from documented references. Verify against your own service info before repair work.
See All Codes & Fixes for Your Vehicle
Explore More
Was this helpful?
Share carcodefinder.com with a friend who needs to decode their check engine light.