P0037: Downstream Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
P0037 means the engine control module found too little voltage or current in the heater circuit of the oxygen sensor behind the catalytic converter on bank 1. It is usually not urgent for driving, but it turns on the check engine light and can cause a failed emissions test.
You can keep driving
The data lists no limp mode for this code and usually no noticeable drivability problem, so short-term driving is generally fine. Get it fixed soon, because the catalyst monitor cannot complete and an emissions test or readiness check can fail.
What it means
The oxygen sensor behind the catalytic converter (sensor 2) mainly checks whether the converter is working. It contains a small heating element that brings it up to operating temperature quickly. Normally the heater gets battery voltage through a fuse, and the engine control module switches the ground side on and off with a pulsed signal while checking that the circuit responds as commanded. P0037 sets when the module measures a voltage or current that is too low in this control circuit, for example from a short to ground or, depending on the system, a burnt-out heating element. Bank 1 is the side of the engine that contains cylinder 1. Each manufacturer defines which exact fault triggers the general, low or high version of the code. Without heat, the sensor is ready late and the catalyst monitor may not complete.
Likely causes
- Control wire shorted to ground, or heating element burnt outVery likely
A short to ground or a failed element (depending on the system) pulls the heater circuit voltage or current too low, which is exactly what this code reports.
- Supply interrupted or fuse blownPossible
If the heater does not receive battery voltage, the circuit reads low when the module checks it.
- Corroded connector with high contact resistancePossible
Corrosion in the plug restricts current flow to the heater and can make the circuit measure low.
- Output driver or software of the engine control moduleLess likely
A fault inside the module that switches the heater ground can cause the code, but this is the least common cause.
What you may notice
- Check engine light on
- Usually no noticeable drivability problem
- Catalyst monitor does not complete
- Emissions test or readiness check failed
What to check, cheapest first
- 1Read the code with a scanner and note any related codes such as P0036, P0038 or P0141, then clear it and see if it returns. · you can do it
- 2Check the fuse for the oxygen sensor heater circuit and replace it if it is blown. · you can do it
- 3Inspect the wiring and connector at the downstream sensor on bank 1 for damage, melted insulation, chafing against the exhaust, or corrosion. · you can do it
- 4Measure the heater element resistance at the sensor and compare it to the specification for the vehicle to see if the element is burnt out. · mechanic
- 5Check for supply voltage at the connector and test the control wire for a short to ground. · mechanic
- 6If the wiring, fuse and sensor test good, check the engine control module output for the heater circuit. · mechanic
Related codes
Frequently asked questions
Can I keep driving with a P0037 code?+
Usually yes. The data lists no limp mode and typically no drivability problem. Repair it soon because the catalyst monitor cannot complete.
Can a loose gas cap cause P0037?+
No. A gas cap affects fuel vapor system codes. P0037 concerns the heater circuit of the downstream oxygen sensor.
Will P0037 pass an emissions test?+
Probably not. The check engine light is on and the catalyst monitor may not complete, so an emissions test or readiness check can fail.
Can I fix it myself?+
Often yes. The repair is rated medium difficulty with an estimated 0.3 to 1.5 hours, and a fuse, connector or sensor replacement can be done at home with basic tools.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10