P0142 moderate

O2 Sensor Circuit Malfunction (Bank 1, Sensor 3)

What does P0142 mean?

The P0142 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit Malfunction (Bank 1, Sensor 3). This is a moderate severity code.

Common Symptoms

  • Check Engine Light on
  • Emissions issue
  • Minor fuel economy change

Probable Causes (Ranked by Likelihood)

  • Failed third O2 sensor (after second catalyst, if equipped) Very High
  • Wiring damage to third sensor High
  • Sensor heater failure Moderate

Step-by-Step Diagnostic Procedure

  1. Locate the Bank 1 Sensor 3 position (typically after the second catalytic converter on longer exhaust systems).

  2. Test sensor voltage, heater resistance, and wiring continuity.

  3. Replace if confirmed faulty.

Frequently Asked Questions

Does my car have three O2 sensors on Bank 1?

Only certain vehicle configurations with two catalytic converters in series on one bank use a Sensor 3 position. Most cars only have Sensor 1 (upstream) and Sensor 2 (downstream).

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