HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
Code P0037 means the heater control circuit for Bank 1 Sensor 2 (downstream O2 sensor) is reading low voltage — the circuit is low when the heater is commanded on. This indicates a short to ground in the heater wiring or an internally shorted sensor heater element.
What You Might Notice
- Check engine light on
- Catalyst monitor may not complete
- May fail emissions test
- No driveability impact in most cases
Most Common Causes
- 1
Short to ground in heater wiring (Bank 1 Sensor 2)
Heater power wire has shorted to ground, pulling circuit voltage low.
- 2
Internally shorted downstream O2 sensor
The heater element inside Bank 1 Sensor 2 has shorted, causing a low-voltage reading.
How to Diagnose It
- 1
Check Short to ground in heater wiring (Bank 1 Sensor 2) — Heater power wire has shorted to ground, pulling circuit voltage low.
- 2
Check Internally shorted downstream O2 sensor — The heater element inside Bank 1 Sensor 2 has shorted, causing a low-voltage reading.
How to Fix It
- 1
Inspect heater wiring for shorts to ground
Check harness near the catalytic converter for chafing against the exhaust or chassis.
- 2
Test heater resistance for internal short
Very low or zero resistance at the sensor heater terminals confirms an internal short.
- 3
Replace Bank 1 Sensor 2 downstream O2 sensor
Install OEM-quality replacement.
- 4
Clear and verify
Confirm heater circuit passes after a drive cycle.
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