P0037 OBD-II Trouble Code: HO2S Heater Control Circuit Low (Bank 1, Sensor 2)

P0037 trouble code definition

P0037 is the code for HO2S Heater Control Circuit Low (Bank 1, Sensor 2)

What the P0037 code means

P0037 indicates that, for the engine to run correctly, the exhaust must have a specific air fuel ratio of 14.7 to 1 as determined by the Heated oxygen sensors (HO2S), which detects the oxygen content of the vehicle exhaust. This information is then sent to the Engine Control Module (ECM) to adjust the amount of fuel delivered to the engine. An HO2S is heated to ensure very rapid data transmission to the ECM’s closed loop system, which helps control emissions during start up and when the engine is cold or warming up.

What causes the P0037 code?

If the code is cleared and reset, and then the Check Engine Light and the OBD-II code comes back, the HO2S sensor for the engine bank 1 and sensor #2, which is to the rear of the catalytic converter, is not sending the correct information to the ECM and may be damaged or defective. The sensor may have a bad internal heater element, or it could have a bad ground, a failed 12 volt battery input or connector. It is quite rare if the ECM is defective.

What are the symptoms of the P0037 code?

The ECM detects the O2 sensor heater circuit low current or an open circuit and will enter failsafe mode until the ignition is turned off. The failsafe mode will cause various drive complaints depending on the vehicle and manufacturer of the vehicle and ECM programming. This failsafe mode will continue until the problem is repaired. Some of the common drive problems in failsafe mode can be hesitation, running rough, and low power. The Check Engine Light will come on once the ECM detects the low control circuit.

How does a mechanic diagnose the P0037 code?

P0037 is only diagnosed with an OBD-II scanner. The mechanic must reset the OBD-II code and test drive the vehicle to see if the code returns. If it comes back, the mechanic should check both power and ground to the sensor including inspecting the wiring and sensor. Many of the problems on this code are wiring-related due to the heat of the exhaust.

Common mistakes when diagnosing the P0037 code

Do not immediately replace the HO2S before checking all related wiring and the connector closely. The mechanic should ensure there is 12 volts to the sensor and the ground is good. Also, check both sides of the connector wiring to ensure the connector is good.

How serious is the P0037 code?

The P0037 code will usually be preceded by the Check Engine Light coming on the vehicle’s dash display while it is in operation. The vehicle can still be driven, but it should be properly diagnosed as soon as possible to prevent more issues like sensor loop errors, high fuel consumption, poor operation, or damage to other components.

Often times, if the Check Engine Light came on immediately at start up, the OBD- II system can be reset and the vehicle will operate normally.

What repairs can fix the P0037 code?

The most common potential repairs to address the P0037 code are as follows:

1. Have a certified technician verify the code with a scanner. Reset the fault codes and perform a road test.

2. If the P0037 code returns, then follow the test procedure. It can have several problems, but wiring being damaged by excessive heat from the exhaust is most common. Make certain the wiring is good and has proper voltage and ground to the sensor before replacing the sensor.

Test Procedure

With the key on and the engine off, use a voltmeter to check for 12+ volts fused battery feed to the heater element. If there is no voltage present, repair the open or short in the 12 volt feed circuit by first determining if it is necessary to replace any fuse blown from the short. If the battery feed is intact, remove the ground (control) circuit from the ECM wiring connector and check for resistance on the circuit. If there is infinite resistance, repair the open in the circuit. If the control circuit checks out, suspect a bad O2 sensor. Replace and re-check.

Having experienced this problem in the past, the most common problem is damage to the sensor wiring, either from improper installation or the wiring clamps failing causing the wires to touch the exhaust system, including the catalytic converter which is the hottest part of the exhaust. The rear sensor is most likely to be removed or exposed to physical damage during work on the exhaust or driveline which creates many potential problems. If the wiring on the sensor itself is damaged, do not try to repair it as it most likely will not work properly. In these cases, just replace the sensor.

Additional comments for consideration regarding the P0037 code

Many vehicles with mileage over 100,000 have momentary sensor problems that usually occur during start up or prolonged stress situations on the drive train. If the Check Engine Light comes on and the vehicle seems to be operating normally, the OBD-II system can be reset using the scanner and the problem may not reoccur. This is why it is important to verify the fault and reset it before doing any repairs.

Need help with a P0037 code?

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