P0037 code: O2 Sensor Heater Control Circuit Low (Bank 1, Sensor 2)
P0037 means o2 Sensor Heater Control Circuit Low (Bank 1, Sensor 2). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0037 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.
P0037 symptoms
- 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 P0037
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 →
How to fix P0037
Easy — basic tools, most owners can do this
- Start at the fuse and count the heater codes
A blown heater fuse kills the feed, and on a ground-switched circuit the engine computer then sees the control side sitting low. If P0037 has company from other heater codes, the shared fuse is the obvious first stop. If a new fuse pops the moment the key goes on, unplug the heaters one at a time to find the shorted branch before fitting another.
- Separate the connector and look for water
Under the floor, this plug takes direct road spray. Pull it apart and look for mud, moisture, white or green crust bridging the pins, or a missing seal. Corrosion linking a heater terminal to a grounded one can pull the circuit low by itself; clean with contact cleaner, dry it, and reseal with dielectric grease.
- Measure the element and test for leaks to ground
With the sensor unplugged, an open reading across its heater terminals means the element is burned out. If it reads normally, unplug the module connector as the service manual directs and check each harness-side heater wire to body ground — continuity points to insulation scraped through on a crossmember, exhaust hanger or heat-shield edge.
- Wiggle-test the underbody run
With the key on and engine off, keep a meter on the control wire at the connector and flex the harness along the floor pan and transmission tunnel. A reading that jumps as you move one section marks an intermittent break or chafe right there, often where a rusted clip has let the loom drop.
- Fit a new sensor and re-secure the harness
When the element tested open, replace Bank 1 Sensor 2 and route the new lead through the original clips, well away from the pipe. A downstream harness left dangling rubs through again, and the next P0037 will be a wiring fault instead of a sensor.
DIY or shop? Fuse, connector and multimeter checks need nothing special, and the downstream sensor is a reasonable swap from underneath with the car properly supported. Where it stops being driveway work is a short to ground you can't locate — some downstream leads join the body loom long before they reach the engine computer — or a sensor rusted into a corroded converter shell. A shop with a lift and the wiring diagram will find a hidden short faster than trial and error.
Tools for the DIY steps: Jack stands or ramps · Multimeter · Spare fuses of the correct rating · Electrical contact cleaner · Dielectric grease · O2 sensor socket
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0037.
Start a case with P0037 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0037?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0037: common questions
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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0037 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0037 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.