02 Sensor Circuit Malfunction (Bank 1 Sensor 3)
Bank 1 Sensor 3 (downstream O2 sensor) circuit malfunction detected. Engine may run rich/lean and emissions increase, but driveability is usually acceptable.
What You Might Notice
- Check Engine Light illuminated
- Decreased fuel economy
- Increased tailpipe emissions
- Possible rough idle
- No noticeable symptoms sometimes
Most Common Causes
- 1
Faulty O2 Sensor
Sensor element degraded or internal failure preventing proper voltage signal.
- 2
Wiring or Connector Issue
Damaged wires, corrosion, or loose connectors interrupting signal to PCM.
- 3
Shorted Signal Wire
Signal wire shorted to voltage, ground, or another circuit causing invalid readings.
- 4
PCM or Module Fault
Rare internal PCM failure in O2 sensor circuit processing.
How to Diagnose It
- 1
Check Faulty O2 Sensor — Sensor element degraded or internal failure preventing proper voltage signal.
- 2
Check Wiring or Connector Issue — Damaged wires, corrosion, or loose connectors interrupting signal to PCM.
- 3
Check Shorted Signal Wire — Signal wire shorted to voltage, ground, or another circuit causing invalid readings.
- 4
Check PCM or Module Fault — Rare internal PCM failure in O2 sensor circuit processing.
How to Fix It
- 1
Replace O2 Sensor
Install new Bank 1 Sensor 3 (downstream/postcat) oxygen sensor.
- 2
Repair Wiring and Connectors
Inspect and repair damaged sensor wiring, connectors, or corrosion.
- 3
Check Sensor Heater Circuit
Verify heater supply voltage and ground connections are intact.
- 4
PCM Reprogramming/Replacement
If wiring and sensor are good, PCM may need reflash or replacement.
Need a deeper diagnosis?
Search for related repair guides or browse by system.