👉 P0145 – O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)

I’ll explain it based on P0145, which matches your description exactly.

🔧 What P0145 Means

Bank 1 Sensor 3 =

Bank 1 → side of the engine with cylinder #1

Sensor 3 → downstream O2 sensor (after the catalytic converter)

Slow response means:

The ECM expects the O2 sensor voltage to change within a certain time

The sensor is reacting too slowly or barely changing

🚗 Common Causes (in real workshop conditions)

Ranked from most common to least:

1. Failing downstream O2 sensor (very common)

2. Exhaust leak near the sensor or after the cat

3. Contaminated sensor (oil, coolant, silicone, fuel additives)

4. Wiring issues

High resistance

Corrosion in connector

Melted wires near exhaust

5. Catalytic converter efficiency issues

6. PCM rarely (last thing to suspect)

🧪 Proper Diagnostic Steps (Professional Approach)

1. Check Live Data (Important)

With scan tool:

Monitor B1S3 O2 voltage

Normal downstream sensor:

Should be fairly steady (0.6–0.8V on gasoline engines)

Faulty slow sensor:

Very lazy movement

Stuck near 0.4–0.5V

Takes too long to respond during throttle snap

👉 Compare Bank 1 Sensor 3 with Bank 2 Sensor 3 if available.

2. Visual & Physical Inspection

Check exhaust leaks before or at the sensor

Inspect wiring:

Burnt insulation

Oil contamination

Loose or green/corroded pins

Make sure sensor is tight and not cross-threaded

3. Heater Circuit Check (Very Important)

Even though this is a “slow response” code, heater problems can cause it.

Check for heater-related codes

Verify:

Battery voltage to heater

Good ground

High resistance heater = slow sensor warm-up = P0145

4. Sensor Test (If Needed)

Propane enrichment or throttle snap

Downstream sensor should respond, but slower than upstream

If response is very delayed or flat → sensor is bad

🔁 Most Common Fix

✅ Replace Bank 1 Sensor 3 O2 sensor

Tips for replacement (shop best practice):

Use OEM or high-quality aftermarket

Avoid cheap universal sensors

Apply anti-seize (if not pre-coated)

Clear codes and perform a drive cycle

🚫 Common Mistakes to Avoid

❌ Replacing catalytic converter first

❌ Ignoring exhaust leaks

❌ Using universal splice-in O2 sensors

❌ Not checking heater circuit

🛠️ Quick Shop Summary

Item Check

Code P0145
Sensor Bank 1 Sensor 3
Location After catalytic converter
Most likely fix Replace O2 sensor
Labor time ~0.5–1.0 hr

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