How To Fix P0031? | HO2S Heater Control Circuit Low (Bank 1, Sensor 1)
What does the P0031 HO2S Heater Control Circuit Low (Bank 1, Sensor 1) mean?
P0031 code gets triggered when the Engine Control Module detects that the voltage in the heater circuit of the oxygen sensor is lower than expected. Specifically, we’re talking about the oxygen sensor heater circuit for Bank 1, Sensor 1.
When the P0031 Triggers?
Your vehicle’s oxygen sensor plays a vital role in monitoring the oxygen content in the exhaust gases. It sends this data to the ECU, which then uses it to maintain the optimal air-fuel ratio
The ECU controls the air-fuel ratio by adjusting the timing of the engine’s valves, allowing just the right amount of air and fuel to enter the combustion chamber.
But here’s the thing: an oxygen sensor won’t function correctly until it’s heated to a certain temperature—around 600°F for conventional sensors. That’s where the heater circuit comes in. It’s designed to warm up the sensor quickly, so it starts working sooner.
The ECU regularly checks the heater circuit in the oxygen sensor to ensure it’s functioning correctly. If it finds that the voltage in the heater circuit for Bank 1, Sensor 1 is lower than expected, it will trigger the P0031 code.
What is Bank 1 Sensor 1?
In engines with multiple cylinder banks, like V6 or V8 engines, you’ll have two sides or “banks” of cylinders. Bank 1 typically refers to the side of the engine where cylinder 1 is located, and Bank 2 is on the opposite side.
Each bank has its own exhaust line, and each exhaust line is equipped with two catalytic converters. Now, here’s where the oxygen sensors come in—each catalytic converter has two oxygen sensors: an upstream sensor, which we call Sensor 1, and a downstream sensor, known as Sensor 2.
So, when we talk about Bank 1 Sensor 1, we’re focusing on the oxygen sensor that’s upstream on the side of the engine where cylinder 1 is located.
How To Fix P0031?
Troubleshooting P0031 involves several steps, and we’ll discuss each one in detail. Let’s get started!
Before diving into specific repairs, perform an OBD-II scanner reset to clear the codes. Sometimes, these codes pop up due to recent maintenance work and can resolve themselves after a reset.
To reset the error codes, use an OBD-II scanner. Simply connect the scanner to your vehicle, follow the instructions to clear the trouble codes, and see if the P0031 code reappears.
If the code comes back, it means there’s a persistent issue that needs further troubleshooting.
Step #1 – Start by visually inspecting the heated oxygen sensor.
Carefully examine the sensor itself, along with the wiring and connectors. Look for any signs of physical damage, such as cracks, frayed wires, or loose connections.
Step #2 – Check for a blown fuse and broken wires.
First, locate your car’s fuse box. You’ll need to find the specific fuse that controls the oxygen sensor heater circuit. To do that, check the diagram on the back of the fuse box cover—it’ll tell you which fuse is the one you’re looking for.
Once you’ve found the fuse, inspect it closely. If the fuse link is broken, it’ll need to be replaced.
Next, check the wiring around the oxygen sensor. Look for any broken or frayed wires. If you spot any damage, repair the wires and recheck to see if the P0031 code is cleared.
If the fuse and wiring are in good condition, but the P0031 code persists. Let’s move on to the next step.
Step #3 – Test the oxygen sensor heater.
Oxygen sensors typically have four wires. Two of these wires, usually of the same color, are dedicated to the heater circuit within the sensor.
To test the heater circuit, you’ll need a multimeter. Set the multimeter to check for continuity, then place the probes on the two heater wires. If the circuit has continuity, the multimeter will beep, indicating that the heater is functioning.
If there’s no beep, it means the heater circuit is broken, and you’ll need to replace the oxygen sensor.
