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P0031 Code: Meaning, Symptoms, Causes, And Fixes


Heated Oxygen Sensor (HO2S) Heater Circuit Low Voltage Bank 1 Sensor 1


The resistance of the heater circuit in bank 1 is too low to heat fuel until it achieves air to fuel ratio of 14:7. The problem is coming from the 1st sensor of bank 1. This code is usually triggered when resistance level is below 0.8A.

Main Symptoms:

Check engine light turns on when you have a P0031 code
When the P0031 trouble code is triggered, Check Engine Light comes on

Possible Causes:

  • Short or open in the O2 heater circuit
  • Defective O2 sensor heater
  • There’s a wiring problem in the circuit leading to the heater. It may be broken or frayed
  • Defective ECM (this is the least likely cause)

Diagnostic Steps:

  • Inspect wiring and power to the O2 sensor and ensure there’s no damage/open/short
  • Use code reader to pull engine codes

Read More: How to Use an OBD-II Scan Tool to Diagnose Your Car

Tim MillerFounderOBD Advisor

I’m Tim Miller from Denver, Colorado. I’m the founder of obdadvisor.com, an automotive blog about "Auto Diagnostic Tools and Repair Guides". My fan page is facebook.com/autozikcom. I've been working as an automotive mechanic and blogger for over 10 years writing articles to share my experiences and expertise.

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