HO2S Heater Control Circuit Low Bank 1 Sensor 2
The Powertrain Control Module (PCM) detected that the heater circuit for the downstream oxygen sensor on Bank 1 (Sensor 2) has a voltage lower than the expected threshold. This typically indicates a short to ground in the wiring or a failure within the sensor's internal heating element.
This code is not an immediate safety hazard and will rarely cause drivability issues. However, it should be diagnosed and repaired soon to restore proper emissions monitoring and pass state inspections.
Common symptoms
- Illuminated Check Engine Light (MIL)
- Failed state emissions test
- Extended time for the oxygen sensor to reach operating temperature
- Slight decrease in fuel economy in some vehicles
- No noticeable drivability issues in most cases
Likely causes
- Failed Bank 1 Sensor 2 oxygen sensor (internal heater element failure)
- Damaged, chafed, or melted wiring harness leading to the oxygen sensor
- Poor electrical connection or corrosion at the O2 sensor connector
- Blown oxygen sensor heater fuse (often caused by a short circuit)
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Scan for additional codes and clear them to see if P0037 returns.
Look for: If the code returns immediately upon starting the engine, it confirms a hard fault in the heater circuit rather than an intermittent glitch.
Visually inspect the wiring and connector for Bank 1 Sensor 2.
Look for: Look for melted wires from exhaust heat, chafing against the chassis, or corrosion and pushed-out pins inside the connector.
Check the oxygen sensor heater fuse(s) in the power distribution box.
Look for: A blown fuse indicates a short circuit, often caused by the O2 sensor wiring touching the hot exhaust pipe.
Measure the resistance of the heater element across the O2 sensor's heater pins using a multimeter.
Look for: An infinite reading (OL) or a reading outside the manufacturer's specification (typically 3-30 ohms) indicates a failed internal heater, meaning the sensor must be replaced.
Verify voltage and ground at the O2 sensor harness connector with the key on, engine off.
Look for: You should see battery voltage (12V) on the power feed and a good ground on the control circuit; a lack of voltage points to a wiring, fuse, or PCM issue.
This page explains the generic P0037 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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