OBD codes / P0037
P0037
ModerateO2 Sensor Heater Control Circuit Low (Bank 1, Sensor 2)
There's no urgency behind the wheel with P0037 — the engine's fuel control doesn't rely on the downstream sensor, so the car drives exactly as before. Treat it as an emissions and inspection issue: get it repaired at a convenient time, and sooner if a smog check is coming up.
What this code means
Behind the catalytic converter on the cylinder-1 side of the engine sits the downstream oxygen sensor — Bank 1, Sensor 2 — whose readings tell the computer whether the converter is actually cleaning the exhaust. Its built-in heater exists so that this monitoring can start soon after a cold start instead of waiting for the exhaust to heat the sensor naturally. P0037 records that the computer measured lower-than-expected voltage in that heater's control circuit: in practice, either the wiring is shorted to ground somewhere, or the heater element inside the sensor has failed open so the circuit goes dead when the heater is switched on. Age is the usual villain — heater elements are consumable parts that eventually burn out — with underbody wiring damage a solid second, since the harness to a downstream sensor lives in the splash-and-salt zone. A blown fuse can produce the same result. Drivability stays normal; the check-engine light and a paused converter monitor are the actual consequences.
Symptoms you might notice
- Check-engine light, typically the only sign
- No noticeable change in power, idle, or fuel economy
- Vehicle will not pass an OBD emissions test with the code set
What it costs to fix
Typical range: $125–$400 · about ~0.3–1.2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Downstream oxygen (O2) sensor | $30–$200 | ~0.3–1.2 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
| Heater-circuit fuse | $1–$10 | ~0.1–0.3 hrs |
Part cost is the smaller variable here; access is the bigger one. Some downstream sensors are easy to reach from underneath, others hide above the exhaust or behind heat shields. Rust-belt cars add time for seized threads and crusty connectors.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0037 for my exact vehicle →
Frequently asked
Can I just clear P0037 and forget it?
You can clear it, but it will return once the computer retests the heater circuit — usually within a drive cycle or two. Clearing also resets the emissions monitors, which need to complete before an inspection, so it doesn't help you pass a test.
What usually causes P0037?
A burned-out heater element inside the Bank 1, Sensor 2 oxygen sensor is the top cause, which means sensor replacement. Underbody wiring shorted to ground and corroded connectors are next — worth a look first, since a downstream harness takes plenty of abuse from road spray.
How is P0037 different from P0036?
Both concern the same downstream heater, but P0036 is a generic circuit fault while P0037 says specifically that the circuit read low — pointing toward a short to ground or a dead-open heater element. That direction helps a technician narrow the diagnosis.
How hard is this repair for a DIYer?
The sensor swap is straightforward with an O2 sensor socket and a way to get safely under the car — ramps or jack stands. The heater wiring runs low along the body, so if the sensor tests fine, chasing the wiring fault takes a multimeter and more patience.
Seeing P0037 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0037 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.