DTC P0063 – HO2S Heater Control Circuit Low (Bank 2 Sensor 1).

✅ P0063 — HO2S Heater Control Circuit Low (Bank 2 Sensor 1)

This code means the upstream oxygen sensor (Bank 2 Sensor 1) heater is drawing too little current → usually caused by an open heater circuit, blown fuse, poor ground, or wiring issue.

🔧 Possible Causes

Most common (90% cases):

1. O2 sensor heater element open (sensor faulty)

2. Blown O2 heater fuse

3. Heater power supply (12V) missing

4. Broken wire / damaged connector

5. Poor ground connection

6. High resistance in the heater circuit

🧰 Quick Checks Before Diagnosis

1. Identify Bank 2 Sensor 1

Bank 2 = side NOT containing cylinder 1

Sensor 1 = upstream (before catalytic converter)

🔍 Step-by-Step Diagnosis

✅ Step 1 — Check O2 Heater Fuse

Most vehicles have:

EFI fuse

O2 heater fuse

ECM/PCM fuse

➡️ If blown → replace.
➡️ If it blows again → wiring short or heater short.

✅ Step 2 — Check Sensor Connector

Look for:

Oil contamination

Water entry

Burned pins

Loose terminals

Fix any corrosion or pin tension issues.

✅ Step 3 — Measure Heater Resistance

Unplug B2S1 O2 sensor.

Typical heater resistance:

3–20 Ω (most cars)

If:

OL / Infinite → heater open → replace sensor

Less than 1 Ω → internal short → replace sensor

✅ Step 4 — Check 12V Power Supply

With ignition ON:

One heater wire must have battery voltage (12V)

If no power:

Blown fuse

Wiring open

Relay/ECM driver issue

✅ Step 5 — Check Ground Control from ECM

The ECM completes the circuit.
Use test light → connect:

Test light to battery (+)

Probe heater ground wire at connector

If test light does NOT flash when engine starts → ECM not grounding.

➡️ Could be wiring open
➡️ Rarely ECM driver faulty

✅ Step 6 — Wiggle Test

While monitoring live data or test light:

Wiggle wiring harness

Look for intermittent heater operation

If flickers → repair broken wire internally.

🛠 Most Common Fixes

🎀 Replace Bank 2 Sensor 1 O2 sensor
🎀 Repair damaged wiring near exhaust manifold
🎀 Replace blown O2 heater fuse
🎀 Clean/repair connector
🎀 Repair heater power wire open
🎀 Repair ECM ground circuit wire

📌 Symptoms of P0063

Check Engine Light

Low fuel mileage

Rough cold start

Engine takes longer to enter closed-loop mode

Welcome to madurai car service 💐🙏.