DTC P004300 – O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 3)

✅ P0043 – O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 3)

Meaning:
The ECM detects low voltage or insufficient current in the heater circuit of the oxygen sensor Bank 1 Sensor 3 (usually the rear-most sensor after the catalyst on some models).

This means the heater element inside the O2 sensor is not heating whew properly, causing delayed readings.

🔧 Common Causes

1. Faulty O2 sensor (heater element open/weak)

2. Blown O2 sensor heater fuse

3. Open or shorted wiring in heater circuit

4. Corroded O2 sensor connector

5. High resistance in heater ground circuit

6. ECM driver fault (rare)

🔎 Step-by-Step Diagnosis

1. Check O2 Sensor Heater Fuse

Locate EFI / O2 Heater / A/F Heater fuse in fuse box.

If blown → Replace fuse.

If it blows again → Sensor or wiring is shorted.

2. Inspect Wiring and Connector (B1S3)

Check for:

Burnt wires near exhaust

Broken insulation

Loose or corroded pins

Oil or water contamination

Repair as needed.

3. Measure Heater Resistance (Sensor Side)

Unplug the O2 sensor → measure resistance of heater pins.

Typical heater resistance:

3–14 Ω (varies by vehicle)

If:

OL / infinite → heater open → replace sensor

Very high resistance → weak heater → replace sensor

4. Check Power Supply to Heater

With key ON (engine OFF):

One pin should have battery voltage (12V)

If no voltage → trace back to fuse or relay.

5. Check Ground Control from ECM

ECM controls heater ground.

Use test light or multimeter to see if ECM switches the circuit when engine is cold.

If no switching → possible ECM driver issue (rare).

🛠️ Most Common Fixes

⭐ Replace O2 sensor B1S3
⭐ Repair damaged wiring near exhaust
⭐ Replace O2 heater fuse
⭐ Clean or replace corroded connector
⭐ ECM repair (last option)

Welcome to madurai car service 💐🙏.