P0037: HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
The heater control circuit for the downstream oxygen sensor on bank 1, after the catalytic converter, is reading low.
What P0037 means
P0037 points to the heater control circuit for the downstream oxygen sensor on bank 1. The computer has measured a low reading on that circuit, which usually means the heater has shorted, the control wire is shorted to ground, or the heater has lost power. RepairPal names oxygen sensor failure, wiring issues and, more rarely, the engine computer as causes. The downstream sensor is mainly used to check the catalytic converter, so drivers usually notice nothing except the check engine light. The catalyst monitor needs a warm, working downstream sensor, though, so the readiness test may not complete and the car can fail an emissions inspection. Shops start with the fuse and connector, then measure heater resistance and check the harness for a short to ground. Downstream wiring often runs close to the exhaust and under the floor, so heat and corrosion damage are common. The fix is usually a sensor, sometimes a wiring repair.
Common symptoms
- Check engine light on
- Usually no change in driveability
- Slightly higher fuel consumption on some cars
- Converter monitor not ready
- Failed emissions or readiness check
Most common causes
- Downstream oxygen sensor heater failure
- Heater control wire shorted to ground
- Blown heater fuse
- Corroded connector under the car
- Engine computer heater driver fault (rare)
What to check yourself first
Check the heater fuse and the downstream sensor connector, which often collects water and road salt. Measure heater resistance across the heater pins. Look for wiring touching the exhaust.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace oxygen sensor | $440-$523 | RepairPal lists replacing the oxygen sensor as the common repair. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | For a shorted or corroded circuit. |
| Check engine light diagnosis at a shop | $125-$183 | Separates a sensor failure from a wiring fault. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
Related repair guides
- Tundra in Limp Mode With Code P2440 or P2442? The Air Injection Pump Problem Explained
- Ram 1500 Ticking on Cold Start? Broken Exhaust Manifold Bolts, Repair Cost and What to Ask
Related codes
- P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)
- P0031 HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
- P0030 HO2S Heater Control Circuit (Bank 1 Sensor 1)
- P0136 O2 Sensor Circuit (Bank 1 Sensor 2)
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)