P0037: HO2S Heater Control Circuit Low (Bank 1 Sensor 2)

What Is P0037?

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

For an engine to run efficiently, it needs the correct air-to-fuel ratio, which is taken care of by the Powertrain Control Module (PCM) or Engine Control Module (ECM) of your vehicle. 

The ECM uses several sensors placed around the engine to accurately measure the fuel-air mixture ratio entering the engine. Oxygen (O2) sensors form a part of this sensor system of your car.

One oxygen sensor is placed before the catalytic converter (oxygen sensor 1) and another after the catalytic converter (oxygen sensor 2 or the downstream oxygen sensor). Bank 1 refers to the side of the engine where cylinder number one is located. E.g., in an inline 4-cylinder engine, there is only one bank (Bank 1).

These sensors often have a heater element to heat them up for accurate readings. They provide feedback to the ECM about any adjustments that need to be made to the air-fuel ratio, which, in turn, affects the engine speed.

A P0037 code links directly to oxygen sensor 2 on Bank 1. If the ECM detects an irregular voltage measurement from this rear oxygen sensor, it stores the P0037 code.

It implies that sensor number 2 at Bank 1 of the engine isn’t receiving the correct battery voltage (0.1V – 0.9V) or heater current to reach its working temperature — and is malfunctioning.

What Are Common Symptoms of P0037?

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

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

◾ An illuminated Check Engine Light: The ECM will illuminate the Check Engine Light after registering a fault code.

◾ Rough idling: This happens when your car’s engine is burning fuel at an inconsistent rate. Rough idling refers to strong engine vibrations or a sudden change in the engine speed at idle.

◾ Burnt smell: Damaged wiring and open circuits can cause electrical components to get short-circuited and burn. Burnt wiring in the O2 sensor wiring harness can cause a smell and result in the code P0037 since the sensor may not receive the correct voltage.

◾ Emission issues: Noticed as either a foul smell or smoke coming from the exhaust.

◾ Poor engine performance: A bad O2 sensor will throw your car’s air-to-fuel ratio off balance. As a result, your car won’t be able to combust fuel properly, resulting in power loss.

◾ Reduced fuel economy: If the fuel-air ratio in the engine is rich, your car will burn more fuel than necessary, leading to poor fuel economy.

Can I Still Drive With P0037?

While the DTC P0037 is not considered a serious problem compared to other fault codes, it shouldn’t be ignored. 

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

What Are P0037 Causes?

Code P0037 can result from the failure of various components in your car.
Here are the most common:

◾ Faulty heater element circuit: A faulty heating element in the downstream oxygen sensor, offering poor heater resistance.

◾ Fuse issues: A blown fuse of the heated oxygen sensor.

◾ Ground errors: Poor chassis ground connection.

◾ Continuity issues: An open circuit between the ECM connector and the heated oxygen sensor. Also, the wiring harness may get damaged by coming in contact with a moving part, such as the drive shaft, and result in a short circuit.

◾ Harness connector problems: Damage to the O2 sensor harness connector. 

◾ ECM errors: Malfunctioning ECM sensor heater driver (unlikely).

How to Diagnose P0037?

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

Here’s what a mechanic would generally do:

1. Use an OBD-II scanner to reset the OBD-II code and test drive the vehicle 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, turn the ignition switch on and use a multimeter to test the battery voltage at the Bank 1 sensor connector. It should read 12 volts with the engine off. Occasionally, the issue may be a poor chassis ground connection or poor rear O2 sensor heater resistance at Bank 1.

3. Check for a blown fuse of the rear sensor. Sometimes the voltage from your car’s battery can blow an old fuse.

4. Inspect the oxygen sensor for any visible damage.

5. Follow the car’s wiring diagram to inspect the wiring harness for any burnt wiring or open circuit issues.

6. Inspect the ECM or the PCM for any damage. The unit may be faulty and distort signals from the O2 sensor.

Here’s what a mechanic would generally avoid:
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 get cleared after resetting with the OBDII scanner. A quick turn of the ignition key will show if the O2 sensor heater circuit code has cleared or not.

3. Attempting to re-wire your vehicle without reference to its wiring diagram.

What Are Possible Repairs & Costs for P0037?

Engine code P0037 can result from a number of faults related to the oxygen sensor. The most important thing is to find out the exact cause of this heater circuit code.

Some common repairs for a P0037 fault code are:

• Heated oxygen sensor replacement
• Blown heated oxygen sensor fuse replacement
• Repair or replacement of damaged wiring or incorrect wiring installations
• PCM or ECM repair or replacement
• PCM or ECM connector repair or replacement

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