Error Code P0037 is defined as (HO2S) Heated Oxygen Sensor Heater Control Circuit Low, Bank 1 Sensor 2. This refers to a problem with the heater element circuit of the HO2S. It’s triggered when the PCM (powertrain control module, also called ECM or engine/electronic control module) detects an excessive low voltage through the HO2S.


The job of the HO2S is to read the oxygen content of the exhaust system and send that information to the PCM. The Bank 1, Sensor 2 refers to Bank 1’s second sensor on the back. The PCM will then use the information to monitor the catalytic converter’s efficiency. Heater element plays a very important component for its function.

For the engine to run properly, the exhaust must have the specified air/fuel ratio of 14.7 to 1. It is the job of the HO2S to determine this ratio and the exhaust’s oxygen content. The sensor sends its reading to the PCM, and the PCM automatically adjusts the level of fuel being delivered to the engine.

The PCM controls the function of the heater, it’s what activates the sensor to warm up and get to its operating temperature. This will allow the engine to enter the closed loop faster and with reduced emissions on cold startup. The PCM also continuously monitors the heater circuit for any abnormal voltages, or in some cases, even the amperages. Oxygen sensor heater is controlled in one of two ways, and that differs in the make of the vehicle/engine. One is that, the PCM directly controls voltage feed that is sent to the heater, either directly or through the HO2S relay, while the vehicle’s common ground supplies the ground. The other way is that, a fused 12V battery feed (B+) which feeds the 12V to heater element at any given moment the ignition is on. A driver in the PCM is provided to control of the heater, which ultimately controls the heater circuit’s ground side.

Knowing which type of vehicle you have is important, as the PCM activates the heater through different circumstances. If the PCM reads that the voltage is too low in its heater circuit, then the Error Code P0037 may be triggered.

Common Symptoms

The primary symptom will be the activation of the Check Engine light.

Should the PCM will detect the problem with the oxygen sensor heater circuit, be it low current or open circuit, it will automatically enter failsafe mode until the engine is turned off. Depending on the manufacturer and the make of the vehicle, this will cause different drivability issues, such as:

  • Hesitation
  • Rough running
  • Lack of power

Possible Causes

The most common cause of this error code is that, the HO2S bank 1, sensor 2 (located at the back of the catalytic converter of the engine) is unable to send the correct data to the PCM, which may suggest damage or a defect with the sensor.

The sensor may have a bad internal heater element. It could also be a case of bad ground or failed 12V battery input or connector.

Some common causes of this error code are:

  • Physical damage on the heated oxygen sensor
  • Failed Bank 1, 2 O2 sensor heater element
  • Failed PCM O2 sensor heater driver
  • Shorted or ground control circuit
  • Or shorted or ground voltage feed

How to Check

To diagnose for this error code, mechanics use the OBD-II scanner to test and re-test the vehicle, and then take it for a test drive to see if the code returns. Should it come back, the mechanic will then check the sensor for both power and ground, including its wiring. Many error codes are actually triggered by faulty wiring.

How to Fix

Conduct a though visual inspection of the Bank 1, Sensor 2 of the HO2S and its wiring harness. Repair or replace any damage to the sensor or its wiring system if needed.

Then, make sure the wiring is properly routed from the exhaust. If everything seems to be in good condition, unplug the HO2S Bank 1, Sensor 2 and check whether there is 12V B+ with the key on, engine off. Depending on the vehicle’s system, you can also check whether there is ground.

Then, check whether the ground for Heater Control circuit is intact. If it is, then remove the oxygen sensor and check for any signs of damage. If you have access to resistance specs of the vehicle, use the Ohmmeter and conduct a resistance test of the heater element. Should you detect infinite resistance, then that means there is a problem of open heater. For this, you need to replace the oxygen sensor.

Wiring damage caused by excessive heat is usually the cause of this error code, along with other related error codes. Thus, fixing usually starts with inspection and repair of any wiring issues. Make sure the wiring system is all in good condition, with proper voltage and ground, before you think of replacing the sensor.

Though you most definitely can drive the vehicle with this error code, it is important to fix it as soon as possible to prevent further issues such as sensor loop errors, poor operation, high fuel consumption, or damage to other components of the engine.