P0037: Heated Oxygen Sensor Heater Control Circuit Low (Bank 1, Sensor 2)

What is P0037?

P0037 is a generic OBD-II diagnostic trouble code (DTC) defined as “Oxygen Sensor Rear Heater Control Circuit Low (Bank 1 Sensor 2).”

For an engine to run efficiently, it needs the correct air-to-fuel ratio. Your vehicle’s powertrain control module (PCM) or engine control module (ECM) ensures that the proper balance of fuel and air is being pumped into the engine.

The powertrain control module or engine control module measures these ratios correctly with the help of sensors placed around the engine. Some of these sensors are oxygen sensors (O2 sensors).

There is one oxygen sensor before the catalytic converter (known as oxygen sensor 1) and another after the catalytic converter (known as oxygen sensor 2). Bank 1 refers to the side of the engine where cylinder one is located. In a 4-cylinder engine, for example, there is only one bank (bank 1).

These sensors give feedback to the powertrain control module on any adjustments that need to be made to the air-to-fuel ratio.

A P0037 code links directly to oxygen sensor 2 on bank 1. For this sensor to give accurate readings, it needs to heat up. To do this, a heating wire (also called a heater element) is placed inside the sensor, quickly heating it to the proper working temperature.

If the PCM detects an irregular voltage measurement from oxygen sensor 2’s heater element, it stores the P0037 code.

In other words, the bank 1 sensor 2 is not receiving the correct battery voltage (0.1V – 0.9V) to reach working temperature and is malfunctioning.

Common symptoms

A P0037 fault code has some noticeable symptoms, which are easy to pick up through daily driving.

These are the most common symptoms of a rear O2 sensor malfunction:

• An illuminated check engine light: The PCM will typically turn on the Check Engine Light for any fault code, which is a general problem indicator.
• Rough idling: This happens when your car’s engine is burning fuel at an inconsistent rate. Rough idling refers to strong engine shaking or a sudden change in RPMs.
• The smell of something burning: Damaged or open circuits can cause electrical components to short and burn. Burnt wiring in the O2 sensors wiring harness can cause the smell and result in a P0037 since the sensor is not receiving the correct voltage.
• Poor emissions: Noticed as either a foul smell coming from the exhaust or smoke.
• Poor engine performance: A bad O2 sensor will cause your car’s air-to-fuel ratio to be incorrect. Your car will not create the correct combustion levels in its engine, resulting in a loss of power.
• Reduced fuel economy: If your air-to-fuel ratio is too rich, your car will use fuel much faster than normal.

Can I still drive?

While the DTC P0037 is not considered a serious problem compared to other fault codes, a P0037 code should not be ignored. Moderate driving is acceptable when your car is experiencing a P0037 code, such as driving it home or to a mechanic for repair.

Driving for extended periods with a bad O2 sensor or P0037 is not advised. Driving with an improper air-to-fuel ratio can cause internal damage to your engine and lead to more problems down the road.

It’s best to fix this code as soon as it is detected.

P0037 causes

The causes of the code P0037 can result from several component failures. Causes can be difficult to pinpoint and require an experienced eye to locate them.

Here are the most common causes:

• Faulty oxygen sensor 2 heater element circuit, offering poor heater resistance (most likely cause)
• Blown heated oxygen sensor fuse
• Poor chassis ground connection
• Open circuit between the ECM connector and HO2S2 (heated oxygen sensor 2)
• Damage to the O2 sensor harness connector wiring.
• Malfunctioning PCM sensor heater driver (unlikely)

Diagnosis

The diagnosis procedure for a P0037 code can be tricky and requires professional equipment and attention to detail to prevent further damage and unnecessary repairs.

Here’s what a mechanic would generally do:

1. Using an OBD-II scanner, a mechanic will reset the OBD-II code and give the vehicle a test drive to see if the code returns. Sometimes, a P0037 code is a simple error or malfunction and needs to be cleared.
2. If the P0037 code returns, the mechanic will turn the ignition switch on and use a multimeter to test the battery voltage measurement of the bank 1 sensor connector (harness connector). Occasionally, the issue may be a poor chassis ground connection or poor bank 1 sensor 2 heater resistance.
3. An inspection will then check for a blown rear sensor fuse. Sometimes the voltage from your car’s battery can blow an old fuse.
4. The mechanic will inspect the oxygen sensor itself for any visible damage.
5. While following your car’s wiring diagram, the mechanic will inspect the wiring harness for any visibly damaged wiring (burnt wiring or open circuit issues). 
6. The mechanic may need to give the PCM a component inspection for any damage or malfunctions. The PCM may be faulty and distorting signals from the O2 sensor.

Here’s what a mechanic would generally avoid doing:

1. Immediately replacing the heated oxygen sensor when they see a check engine light. Replacing the heated rear sensor before ruling out all other potential problems could be costly.
2. Not resetting the fault code before attempting repairs. Sometimes, the code is just an error and will clear after resetting it with the OBD11 scanner. A quick turn of the ignition switch will show if the heater circuit code has cleared or not.

Attempting to re-install your car’s wiring without reference to the vehicle’s specific wiring diagram.

Possible repairs for P0037 & Costs

Engine code P0037 results from any number of faults related to the oxygen sensor. The most important thing is finding out the exact cause of the fault code.

Some common repairs for a P0037 fault code are:

• Replacing the heated oxygen sensor
• Replace a blown heated oxygen sensor fuse
• Repair or replacement of damaged wiring or incorrect wiring installations
• ECM or PCM repair or replacement
• PCM or ECM connector repair or replacement
  

The diagnosis can take between 1-2 hours, and the total labor costs for a DTC P0037 are between $75-$150 — depending on the mechanic’s rate.