P0038 High HO2S Heater Control Circuit (Bank 1 Sensor 2)

Definition of Code P0038

Code P0038 is a generic powertrain code that indicates a problem in the heated oxygen sensor (HO2S) heater control circuit located downstream of the catalyst on bank 1 (Bank 1 Sensor 2).

Specific Definitions

• Generic: HO2S Heater Control Circuit High (Bank 1 Sensor 2)
• Nissan Specific: Heated Oxygen Sensor (HO2S) 2, Bank 1 – High Heater Voltage

This Diagnostic Trouble Code (DTC) applies to all OBD-II compliant vehicles (from 1996 onwards), including Toyota, Volkswagen, Ford, Dodge, Honda, Chevrolet, Hyundai, Audi, Nissan, etc.

🛠️ Repair procedures may vary depending on the vehicle’s make, model, and year.

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HO2S Sensor Operation and Fault Causes

Modern engines are equipped with heated oxygen sensors (HO2S) that provide essential data to the Powertrain Control Module (PCM) to monitor catalyst efficiency.

The Bank 1 Sensor 2 HO2S is located after the catalytic converter. It includes an integrated heating element that helps it reach optimal operating temperature more quickly, allowing the system to enter closed-loop operation faster for better air/fuel mixture management.

Typical Sensor Configuration

Modern sensors typically have 4 wires:

• 2 wires for the O₂ signal
• 2 wires for the heating element

The PCM controls and monitors the heating element according to two possible configurations:

1. Direct control via the PCM or an HO2S relay, with ground provided by the chassis
2. Constant 12V power supply (B+), with the PCM controlling the ground side via an internal circuit

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Symptoms of Code P0038

• Illuminated Malfunction Indicator Lamp (MIL / Check Engine)
• Possible increase in fuel consumption
• Failure of emissions tests
• No other noticeable symptoms in most cases

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Possible Causes of Code P0038

• Faulty HO2S Bank 1 Sensor 2
• Open (cut) heater control circuit
• Short circuit to battery voltage (B+)
• Open ground circuit
• Short circuit to ground in the control circuit
• PCM failure (rare)

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Diagnosis and Solutions for P0038

1. Preliminary Visual Inspection

• Check the HO2S Bank 1 Sensor 2 and its wiring harness
• Look for damaged, melted, exposed wires, or contact with the exhaust
• Repair or replace any damaged components

2. Electrical Verification

• Disconnect the sensor and measure the supply voltage (12V B+)
• Check for continuity and absence of short circuits on the circuits
• Test for a good ground on the control wire

3. Heater Element Test

• Remove the sensor if necessary
• Using an ohmmeter, test the heater element’s resistance according to manufacturer specifications
• Infinite resistance indicates an open circuit, meaning a faulty sensor

4. Sensor Replacement

• If the heating element is out of specifications, replace the HO2S
• Use an OEM quality or equivalent sensor
• Clear the fault codes after repair

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Consequences and Recommendations

This code does not directly affect engine performance, but it can interfere with cold fuel management and prevent catalyst diagnostic tests.

A new or high-quality sensor is recommended to avoid premature failures. If in doubt about the wiring or PCM, consult a qualified technician.