P04700 – O₂ Sensor Heater Circuit Bank 1 Sensor 3 (commonly written as P0470 / P04700 depending on scanner).

What the code means

Bank 1 Sensor 3 (B1S3) is the downstream oxygen sensor after the catalytic converter on Bank 1.

The code indicates a problem with the heater circuit, not the sensor’s oxygen reading itself.

The heater helps the O₂ sensor reach operating temperature quickly. If the heater isn’t working, the ECU sets this code.

Common Causes 

1. Burnt or open heater circuit inside the O₂ sensor

2. Blown O₂ heater fuse

3. Damaged wiring (very common near exhaust)

4. Bad ground or poor connector contact

5. ECU issue (rare)

Quick diagnostic steps (technician workflow)

💥 Visual inspection (don’t skip)

Check wiring near exhaust and cat:

Melted insulation

Broken or stretched wires

Unplug the sensor and look for:

Corrosion

Loose or pushed-back pins

> ⚠️ 70% of these codes are wiring or sensor failure.

💥 Check heater resistance (sensor test)

Unplug B1S3 O₂ sensor

Measure resistance across heater pins (usually same-color wires)

Typical spec:

5–20 ohms (varies by manufacturer)

Results:

∞ (open circuit) → Replace sensor

0–1 ohm → Shorted heater → Replace sensor

💥 Check power supply (key ON)

One heater wire should have battery voltage

If no voltage:

Check O₂ heater fuse

Check relay (if applicable)

💥 Check ground control

Other heater wire is ECU-controlled ground

Use test light or scope:

ECU should pulse ground after startup

No ground = wiring or ECU issue

💥 Clear code & road test

Clear codes

Drive until closed loop

If code returns → confirm repair

Customer symptoms

Check engine light

Usually no drivability issue

Possible:

Slight MPG drop

Failed emissions test

Repair recommendation (what usually fixes it)

Replace Bank 1 Sensor 3 O₂ sensor
(Use OEM or high-quality brand — cheap sensors cause repeat comebacks)

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