P0031 Code – HO2S Heater Control Circuit Low


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