O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 1
Diagnostic trouble code P2238 indicates that the powertrain control module (PCM) has detected a low voltage condition in the positive current control circuit of the Bank 1, Sensor 1 oxygen (A/F) sensor. This means the sensor's signal is falling below the expected operating range, suggesting an issue with the sensor itself or its wiring.
While the vehicle will typically still drive, this code affects the engine's air/fuel ratio management. Prolonged driving with this issue can lead to decreased fuel economy, poor performance, and potential premature wear on the catalytic converter.
Common symptoms
- Illuminated Check Engine Light
- Decreased fuel efficiency
- Rough engine idle
- Hesitation or sluggish acceleration
- Strong exhaust odor (running rich)
Likely causes
- Defective Bank 1 Sensor 1 Oxygen (Air/Fuel Ratio) Sensor
- Damaged, frayed, or melted wiring in the O2 sensor circuit
- Corroded or loose electrical connector at the O2 sensor
- Blown fuse for the O2 sensor heater circuit
- Exhaust leak near the Bank 1 Sensor 1 location
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Visually inspect the Bank 1 Sensor 1 O2 sensor wiring and connector.
Look for: Look for melted, chafed, or broken wires, and check the connector for corrosion, water intrusion, or loose pins. Any physical damage indicates a wiring repair or replacement is needed.
Check the O2 sensor heater circuit fuse.
Look for: Locate the fuse for the O2 sensor heater in the fuse box and test it for continuity. A blown fuse suggests a short circuit in the wiring or the sensor itself.
Measure the voltage at the O2 sensor connector.
Look for: Using a multimeter, check for proper reference voltage and ground at the sensor connector with the key on, engine off. Lack of voltage indicates a wiring issue between the PCM and the sensor.
Test the O2 sensor internal resistance.
Look for: Measure the resistance across the heater circuit pins of the O2 sensor. If the resistance is out of the manufacturer's specified range or shows an open circuit, the sensor is faulty and must be replaced.
Inspect for exhaust leaks near the sensor.
Look for: Listen for ticking sounds or feel for escaping exhaust gases around the exhaust manifold and pipes upstream of the sensor. An exhaust leak can introduce unmetered oxygen, skewing the sensor readings.
This page explains the generic P2238 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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