DTC P0142 – O2 Sensor Circuit (Bank 1 Sensor 3) for your car service business.

✅ DTC P0142 — O₂ Sensor Circuit (Bank 1 Sensor 3)

Meaning

This code indicates that the third oxygen sensor on Bank 1 is showing a circuit problem (usually low activity, slow response, or incorrect voltage).

👉 Bank 1 = side with cylinder 1
👉 Sensor 3 = downstream O₂ sensor after the second catalytic converter (found usually in V6/V8 and dual-cat systems)

🔧 Symptoms

Check Engine Light ON

High emissions

Poor fuel economy

Sometimes no drivability issue

🛠 Possible Causes

1. Faulty O₂ sensor (Bank 1 Sensor 3)

2. Damaged wiring or connector

melted wires near exhaust

broken insulation

3. Blown heater fuse (if sensor has heater circuit)

4. Exhaust leak after catalytic converter

5. ECU driver issue (rare)

🔍 Step-by-Step Diagnostic Guide

1. Visual Inspection

Lift vehicle and inspect B1S3 wiring & connector

Look for:

burnt wires near exhaust pipe

loose connector

corrosion in pins

➡️ Repair any damaged wiring first.

2. Check Sensor Voltage (Using Scanner)

B1S3 should stay mostly stable ~0.6–0.8V
(downstream sensor shows steady reading; upstream sensors fluctuate)

If:

Stuck at 0V → open circuit / wiring issue / bad sensor

Stuck at 1V → short to power / rich condition / bad sensor

Slow response → failing sensor

3. Check Heater Circuit

Since most S3 sensors have heaters:

Test resistance across heater terminals
Typical spec: 3–15 ohms

If open circuit → sensor heater failed → replace sensor.

4. Check Power & Ground

Using multimeter:

12V supply from heater fuse

Good ground continuity

If missing → repair power/ground circuit.

5. Check Exhaust System

Ensure no leaks near or after catalytic converter
A leak can confuse downstream sensor readings.

6. Replace Sensor (If Confirmed Faulty)

Use OEM quality O₂ sensor only

Apply anti-seize if sensor manufacturer recommends

Clear codes and test drive

🎯 Quick Fix Summary

Issue Fix

Sensor dead / no voltage Replace B1S3 O₂ sensor
Wiring burnt / loose Repair wires, connectors
Heater circuit open Replace sensor or fix fuse
Exhaust leak Weld/repair leak
ECU issue ECU repair (rare)

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