P0037 is a generic OBD II trouble code, which means that it has the same meaning for the Toyota Tacoma as it would for any other car or truck. Diagnosing this code is relatively straightforward. It is usually caused by a bad oxygen sensor, or a wiring issue. This code is closely related to P0031 (same issue, sensor 1 instead of 2).
P0037 Definition + Sensor Location
Bank 1 Sensor 1 Location
- Bank 1 is the side of the engine with cylinder 1. If you have a four cylinder engine or inline six, it’s the only bank.
- Sensor 2 is the second sensor when tracing the exhaust from bank 1.
When the engine is cold, the ECM/PCM has a hard time getting a good reading from the Tacoma’s oxygen sensors. Without a good reading, it is difficult for it to determine the proper air/fuel mixture to give the engine. The heated element in the oxygen sensor heats it up to help get a more accurate reading of the oxygen level in the exhaust gas.
The job of the O2 sensors in your Tacoma is to measure the level of oxygen in the exhaust so that the ECM can make changes to the air/fuel ratio. As stated above, the oxygen sensor has a heater that helps to give it a more accurate reading. When this heater is not operating, it can affect the way that the engine runs. With P0037, the O2 sensor is informing you that the heater circuit resistance is lower than the normal operating range.
This code will often appear with P0171. It indicates that the Tacoma has a lean condition. If these are the only two codes present, fixing what is causing P0037 will more than likely clear the P0171.
Toyota Tacoma: P0037 Symptoms
P0037 is most often not accompanied by any noticeable symptoms as long as it is the only code that is currently stored in the ECM’s memory. If there are symptoms, they’ll be:
- Service Engine Soon Light
- Diminished Fuel Mileage
- Rough Running Engine
- Raw Fuel Smell Coming From Exhaust (particularly when cold)
If the engine is running rough, it very well may be accompanied by the P0300 code. This indicates a random misfire in all of the cylinders.
P0037 Causes: Toyota Tacoma
The most common cause of P0037 is a bad oxygen sensor. It’s, not the only cause though. A quick examination of the Tacoma’s physical wiring harness, as well as the voltage coming from the heated O2 sensor can save you from buying a sensor that you don’t need.
1. Wiring Issue
Due to the location of the oxygen sensors (under your Tacoma, on the hot exhaust pipes), the wiring harness around them is easily susceptible to damage. Hot exhaust can make the wiring harness brittle. A visual inspection will often uncover exposed wiring (that’s shorted) or wiring that is broken altogether. Pay particular attention to anywhere that the harness comes close to touching other metal, and where it is closest to the exhaust.
If the harness looks like it is intact, you’ll next want to to test and make sure that the heated oxygen sensor is getting power. You can take a simple test light and check to see if the harness is getting voltage. If it’s not, check the fuse. Make sure to test the ground circuit for continuity.
If the oxygen sensor is getting power to it, you can check to see if it is getting the correct level of voltage/ohms. Here’s a great video from Ratchets and Wrenches on how to test the wiring on a heated O2 sensor:
2. Oxygen Sensor
It is highly likely that the oxygen sensor has gone bad when you get this code. The good news is, they are affordable and easy to replace.
3. Bad ECM
It is technically possible that the ECM has gone bad when everything seems to be working, but you still get this code anyway. It’s not very likely though. Here’s more on the symptoms of a bad ECM.
Conclusion: P0037 Tacoma
This code is relatively straightforward to diagnose. You’re more than likely going to be changing one of your Tacoma’s oxygen sensors. If there is anything that you would like to add, please feel free to leave a comment below.