# "Heater Control Circuit Low" P0031



## pscd27 (Jan 12, 2005)

Not sure if anyone can help me with this. I have a 2002 Sentra SE-R and my check engine soon light came on. So I went to autozone and did the free diagnostic test. They said the issue # was P0031 and "Heater control circuit low". Has anyone come across the same problem and if so, what does it mean? Thanks for your help.


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## lshadoff (Nov 26, 2002)

P0031 is a malfunction in the first Oxygen Sensor Heater. The ECU detected a voltage which is too low.

This is due to either a bad connection or a defective O2 sensor.

Lew


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## pscd27 (Jan 12, 2005)

Perfect! Thanks for your help. So the 02 sensor basically monitors the air going to the engine...


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## pscd27 (Jan 12, 2005)

Actually, I take that back. Does is monitor the exhaust?


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## lshadoff (Nov 26, 2002)

pscd27 said:


> Perfect! Thanks for your help. So the 02 sensor basically monitors the air going to the engine...


The O2 sensor is in the exhaust, and measures unconsumed oxygen. This is related to the air-fuel ratio going into the cylinders.

The Mass Airflow Meter (MAF) measures the air going into the engine.

Lew


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