P0037 Code: O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
By understanding the P0037 code and its implications, car owners can take a more proactive approach to maintaining their vehicles, ultimately saving time, money, and ensuring their car runs at its optimal level.
Quick Answer
P0037 means the engine computer has detected a low electrical condition in the Bank 1 Sensor 2 oxygen-sensor heater control circuit. Sensor 2 is the downstream oxygen sensor located after the catalytic converter. The code does not automatically prove that the sensor itself is bad. Check the heater fuse or power supply, exhaust-damaged wiring, connector terminals, and heater resistance before replacing parts. If testing confirms an open or out-of-spec heater, replace the correct direct-fit downstream sensor and verify that the monitor completes without P0037 returning.
Safety note: Let the exhaust cool before inspection. If you must work underneath the vehicle, use the manufacturer-approved lifting points and properly rated support stands. Never rely on a jack alone.
What Does P0037 Mean, and Where Is B1S2?
The full definition is HO2S Heater Control Circuit Low, Bank 1 Sensor 2. “HO2S” means heated oxygen sensor. Its heater brings the sensing element up to operating temperature quickly after a cold start, allowing the emissions system to begin monitoring sooner.
Bank 1 is the side of the engine containing cylinder No. 1. An inline engine has only one bank. On a V-engine, Bank 1 may be on either side, so do not assume it is always the driver or passenger side. Sensor 2 is the downstream sensor installed after the catalytic converter. For a visual explanation, see A-Premium’s guide to upstream and downstream O2 sensors.
How Is P0037 Different From Similar O2-Sensor Codes?
| Code | Circuit Identified | Key Difference |
|---|---|---|
| P0037 | Bank 1 Sensor 2 heater control circuit low | Electrical heater-control fault |
| P0137 | Bank 1 Sensor 2 signal circuit low voltage | Concerns the sensor signal, not specifically the heater |
| P0141 | Bank 1 Sensor 2 heater circuit malfunction | Broader heater-performance fault |
| P0038 | Bank 1 Sensor 2 heater control circuit high | High rather than low circuit condition |
| P0057 | Bank 2 Sensor 2 heater control circuit low | Same fault family on Bank 2 |
How Serious Is P0037, and What Are the Symptoms?
P0037 is usually not an immediate breakdown code. Because the downstream sensor mainly monitors catalytic-converter performance, many vehicles continue to start, accelerate, and idle normally. However, the failed heater can delay sensor warm-up, prevent the oxygen-sensor heater monitor from completing, keep the Check Engine light on, and cause an emissions inspection failure. Leaving the fault unresolved also hides whether the catalyst-monitoring system is functioning as designed.
A steady warning light with otherwise normal operation generally allows a careful trip to a repair facility. Stop driving and investigate separately if the light flashes, the engine misfires heavily, the exhaust becomes unusually hot, or the vehicle loses power. Those are not normal consequences of P0037 alone and may indicate another fault that could damage the catalytic converter.
Common Symptoms of P0037
- Check Engine light
- P0037 stored or pending in the ECM
- Oxygen-sensor heater or emissions readiness monitor not complete
- Failed emissions inspection
- Little or no noticeable change in everyday drivability
Poor fuel economy, rough idle, hesitation, or stalling should prompt a scan for additional codes and a wider engine diagnosis. Do not automatically attribute those symptoms to the Bank 1 Sensor 2 heater.
What Causes P0037?
- Open or out-of-spec heater element: the heater inside the downstream O2 sensor can fail electrically.
- Fuse, relay, or power-feed problem: the heater may not receive its specified supply voltage.
- Heat-damaged wiring: a harness routed too close to the exhaust can melt, chafe, or short.
- Connector damage: loose locks, spread terminals, corrosion, moisture, or overheated pins can add resistance or interrupt the circuit.
- Open, short-to-ground, or high-resistance circuit: the fault may be between the sensor and ECM rather than inside the sensor.
- ECM/PCM driver fault: possible, but uncommon and considered only after the sensor, power supply, connector, and harness pass testing.
Diagnostic shortcut: If several O2-heater codes appeared at the same time, inspect the shared fuse, relay, power feed, and harness routing before buying multiple sensors. If a replacement fuse blows again, locate the short instead of installing another fuse.
How Do You Diagnose P0037?
Diagnose the electrical path in a fixed order so one code does not become an unnecessary sensor purchase:
- Use an OBD-II scanner to record stored and pending codes plus freeze-frame data. Do this before clearing anything.
- Confirm the exact B1S2 location using the year, make, model, engine, and vehicle-specific service information.
- Look for other heater codes. Check the specified heater or EFI fuse and relay; do not rely on a generic fuse number.
- With the exhaust cool, inspect the harness near the exhaust pipe, heat shields, clips, and underbody. Look for melted insulation, rubbing, previous splices, or impact damage.
- Disconnect the connector as directed and inspect the lock, seal, pins, and terminals for looseness, corrosion, water, or heat discoloration.
- Measure heater resistance at the correct sensor terminals and compare it with the exact service specification. An open reading or out-of-range result can support sensor replacement.
- Verify the specified power feed and the ECM-controlled side of the circuit. Follow the service procedure because heater-control strategies differ.
- If necessary, test continuity, shorts, and voltage drop between the sensor and ECM. Consider module testing only after the rest of the circuit passes.
| Test Result | What It Means | Next Step |
|---|---|---|
| Heater is open or outside specification | Internal heater may have failed | Confirm terminals, then replace the correct sensor |
| No specified power at the connector | Supply-side fault | Check fuse, relay, and power-feed wiring |
| Power is present but the control path is open | Harness or connector fault | Repair the circuit before replacing the sensor |
| Fuse blows again | Short or excessive current remains | Locate the short before fitting another fuse |
| Sensor and circuit pass | Intermittent terminal or module issue is possible | Use the OEM intermittent-fault and ECM test procedure |
Avoid electrical damage: Do not apply battery voltage to sensor or ECM terminals, pierce sealed wires, or guess at pin functions. Use the correct wiring diagram, terminal test method, and meter settings for the vehicle.
How Do You Fix P0037?
Match the repair to the confirmed result. Repair damaged wiring and restore heat-safe routing; replace corroded or heat-damaged terminals or the connector pigtail; correct a fuse, relay, or power-feed fault only after finding its cause; and replace B1S2 when the internal heater fails its specified test. ECM diagnosis is a final step, not a first guess.
Do not replace the upstream sensor, catalytic converter, or every O2 sensor simply because P0037 is stored. One confirmed Bank 1 Sensor 2 heater fault normally calls for one targeted repair.
Why Choose A-Premium Parts to Repair P0037?
Diagnosing a failed Bank 1 Sensor 2 oxygen sensor is hard enough—finding the exact replacement shouldn't be. A-Premium simplifies your repair with guaranteed-fit precision.
- Precision Fit Mentality: Filter by exact year, engine, emissions, and B1S2 location to get the right sensor the first time.
- Plug-and-Play Easy: Direct-fit connectors preserve OEM wiring—no splicing, no guesswork, no extra delay.
- Zero-Risk Protection: Backed by 90-day free returns, fast free shipping, 24/7 support, and full warranty protection.
How Much Does P0037 Cost to Fix?
The cost depends on whether P0037 comes from a small electrical fault, the downstream sensor, inaccessible wiring, or the ECM. The following U.S. figures are planning ranges, not vehicle-specific quotes:
| Confirmed Repair | Typical U.S. Range | Main Cost Driver |
|---|---|---|
| Electrical diagnosis | About $80–$200 | Pinpoint testing time and local labor rate |
| Fuse, terminal cleaning, or simple connection repair | About $50–$250 | Whether the underlying short is easy to find |
| Connector pigtail or localized wire repair | About $150–$500 | Access, number of damaged wires, and sealing/routing work |
| Oxygen-sensor replacement | Average $300–$450 | Vehicle-specific sensor price, corrosion, and access |
| Extensive harness repair | About $400–$1,500+ | Harness length, disassembly, and heat or impact damage |
| ECM replacement and programming | Often $900–$1,600+ | Module source, programming, and confirmed driver failure |
How Do You Confirm the P0037 Repair?
- Confirm the wiring is secured away from the exhaust and the connector is fully locked.
- Clear the code only after the repair is complete.
- Run the manufacturer’s confirmation procedure or appropriate drive cycle.
- Rescan for stored and pending codes.
- Check whether the oxygen-sensor heater and emissions readiness monitors have completed.
If P0037 returns immediately, prioritize a hard open, short, missing power supply, or failed heater. If it returns intermittently, inspect for loose terminals, heat-related expansion, vibration, moisture, or a harness that moves into contact with the exhaust. Clearing the light without repairing the circuit resets readiness monitors and does not prove the vehicle will pass inspection.
FAQs
Can I drive with a P0037 code?
Usually, a vehicle with only P0037 and a steady Check Engine light remains drivable for a short trip to diagnosis. Do not ignore the code because readiness and emissions testing may be affected. Stop if the light flashes or severe drivability symptoms appear.
Can a blown fuse cause P0037?
Yes. A heater power-supply fuse can cause P0037, especially when several heater codes appear together. If the fuse blows again, find the short or excessive-current condition before replacing it again.
Is Bank 1 Sensor 2 upstream or downstream?
Bank 1 Sensor 2 is downstream of the catalytic converter on the cylinder No. 1 bank. On an inline engine, there is only Bank 1.
Does P0037 always mean the oxygen sensor is bad?
No. A failed internal heater is one cause, but the fuse, relay, connector, power feed, control wire, or ECM driver can also set the code. Test the circuit before replacing the sensor.
Can I test the O2-sensor heater with a multimeter?
Yes, if you have the correct wiring diagram, terminal identification, and resistance specification for the vehicle. Do not guess at terminals or apply battery voltage to the circuit.
Will clearing P0037 make the car pass an emissions test?
Not by itself. Clearing codes resets readiness monitors. The fault must be repaired, the required monitors must run, and P0037 must not return.
