Possible causes

– Faulty Front Heated Oxygen Sensor (HO2S) Bank 1
– Front Heated Oxygen Sensor (HO2S) Bank 1 harness is open or shorted
– Front Heated Oxygen Sensor (HO2S) Bank 1 circuit poor electrical connection
– Inappropriate fuel pressure
– Faulty fuel injectors
– Intake air leaks may be faulty
– Exhaust gas leaks

Tech notes

Replacing the Front Heated Oxygen Sensor (HO2S) Bank 1 usually takes care of the problem

When is the code detected?

The Powertrain Control Module (PCM) monitors the HO2S voltage for being fixed below a predetermined voltage. If the PCM detects the voltage is below a predetermined voltage, the P0131 code is set.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– High Fuel Consumption
– Excessive Smoke from Exhaust

P0131 SATURN Description

The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between the Front Heated Oxygen Sensor (HO2S) high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.
The PCM monitors and stores the heated oxygen sensor (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if majority of the samples are out of the operating range.

SATURN Technical Service Bulletins for P0131 code