What it means
The heater control circuit for the Bank 1 Sensor 1 heated oxygen sensor is reporting voltage below the expected range.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The heater in the upstream bank 1 sensor 1 oxygen sensor warms the sensor so it can provide useful exhaust readings soon after startup. The module sets P0031 when the heater control circuit voltage is too low, which can result from a wire shorted to ground, an internally shorted heater, or poor connector contact.
Common causes
Most likely first.
- Heater control wire shorted to ground
- Heater element internally shorted
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Increased emissions
- Reduced fuel economy
- Failed emissions test
How to diagnose it
- Record freeze-frame data and check for companion heater or oxygen-sensor codes before clearing the fault.
- Inspect the upstream bank 1 sensor 1 connector and wiring for chafing, heat damage, moisture, or corrosion that could pull the control circuit low.
- Check the heater fuse and connector terminals for a poor fit or corrosion, using the wiring diagram to identify the correct circuit.
- Test the heater control wire for a short to ground and check the sensor heater circuit using the manufacturer's diagnostic procedure.
- If wiring and connections pass, test the sensor heater and module control to distinguish an internal heater fault from a control fault.
Common fixes
- Reconnect or clean the bank 1 sensor 1 heater connector if contact is poor.
- Repair wiring rubbed through to ground or damaged by exhaust heat.
- Replace corroded or loose connector terminals.
- Replace the upstream bank 1 oxygen sensor if its heater is internally shorted.
Can I keep driving?
Driving is generally possible if the engine runs normally, though emissions can be higher before the sensor warms and fuel economy may worsen. Get it repaired soon and avoid relying on the vehicle to pass an emissions test until the fault is fixed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.