HO2S Heater Control Circuit High Bank 1 Sensor 2
Diagnostic trouble code P0038 indicates that the powertrain control module (PCM) has detected a higher than expected voltage in the heater control circuit for the downstream oxygen sensor on Bank 1 (Sensor 2). This means the PCM is seeing a short to voltage or excessive resistance in the heater circuit, preventing the sensor from reaching its optimal operating temperature quickly.
This code does not typically cause drivability issues or pose an immediate safety risk. However, it should be addressed to ensure proper emissions monitoring and to prevent the vehicle from failing an emissions test.
Common symptoms
- Illuminated Check Engine Light (MIL)
- Failed emissions test
- Slight decrease in fuel economy
- Engine may stay in open loop longer than normal upon startup
- No noticeable drivability symptoms in most cases
Likely causes
- Failed Bank 1 Sensor 2 oxygen sensor (internal heater element failure)
- Short to voltage in the O2 sensor heater circuit wiring
- Corroded, damaged, or loose connector at the O2 sensor
- Blown O2 sensor heater fuse (often caused by a short)
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Visually inspect the wiring and connector for Bank 1 Sensor 2.
Look for: Look for melted, chafed, or broken wires, especially near the exhaust pipe. Check the connector for corrosion, water intrusion, or loose pins.
Check the O2 sensor heater fuse.
Look for: Locate the fuse for the O2 sensor heaters in the fuse box and check if it is blown. A blown fuse indicates a short circuit that must be found before replacing the fuse or sensor.
Measure the resistance of the O2 sensor heater element.
Look for: Disconnect the sensor and use a multimeter to measure resistance across the heater pins on the sensor side. An open circuit (infinite resistance) or a reading out of the manufacturer's specification indicates a failed sensor.
Check for voltage at the O2 sensor heater connector.
Look for: With the key ON and engine OFF, measure the voltage on the harness side of the connector. You should see battery voltage (approx. 12V) on the power feed wire. If voltage is present on the ground/control side when it shouldn't be, there is a short to voltage in the wiring.
Test the ground/control circuit from the PCM.
Look for: Verify that the PCM is providing a ground to the heater circuit (often pulse-width modulated). If the wire has continuity to the PCM but no ground is provided when commanded, the PCM may be faulty.
This page explains the generic P0038 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.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.