P0038 – O2 Sensor Heater Control Circuit High (Bank 1 Sensor 2)

✅ DTC P0038 – Meaning 

Bank  Sensor 2 = downstream O₂ sensor (after catalytic converter).
Circuit High = the heater control circuit has higher than expected voltage, usually due to:

Open circuit

Short to battery voltage

Poor ground

Faulty sensor heater element

Wiring damage

🔧 Common causes

1. Faulty O₂ sensor (B1S2) heater element
2. Short to battery in heater power supply

3. Open circuit in heater ground

4. Blown or damaged fuse (O2 heater fuse)

5. Corroded or loose connector

6. ECM/PCM driver fault (rare)

🧰 Step-By-step diagnostic procedure

1.Confirm the Power Supply to Heater

Key ON (engine OFF)

Check the O₂ heater B+ supply pin on the O₂ sensor connector
Expected reading: 12V

If you see more than 12–14V, wiring may be shorted.

2. Check the Ground Side (Control Side)

The ECM usually switches the heater ground.

Using a test light between battery positive & heater ground pin:

Light ON = ground OK

No light = broken ground circuit or ECM driver issue

If the ECM wire shows constant battery voltage, it indicates: ✔ short to power

3.Check Resistance of Heater Element

Disconnect O₂ sensor & measure heater resistance:

Normal: 3–15 ohms (varies by vehicle)

Over 20–30 ohms = heater open → replace sensor

0–1 ohm = shorted heater → replace sensor

4. Inspect Wiring Harness

Look for:

Wires touching exhaust pipe → melted insulation

Rodent damage

Corroded connector pins

Oil contamination inside connectors

Pay special attention to the heater power wire (usually white).

5. Check O₂ Heater Fuse

Some vehicles have a dedicated fuse:

“HTR”, “A/F HTR”, “O2 Heater” etc.
If the fuse keeps blowing:
→ heater circuit short to ground or shorted heater in sensor.

6. Replace Bank 1 Sensor 2 if Needed

If:

Heater resistance is bad

No wiring damage

Fuse OK

Then the sensor is faulty → replace B1S2 O₂ sensor.

7. ECM/PCM Driver Check (Last)

Only if:

Power supply OK

Wiring OK
New O₂ sensor still gives P0038

Then ECM heater driver may be stuck HIGH.

Very rare.

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