P0038 OBD2 Trouble Code ✔️ Time to look at some wires!

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P0038 OBD2 Trouble Code

Meaning of P0038 OBD2 Code

The technical definition of P0038 code is: Oxygen Sensor Heater Control Circuit High in Bank 1 Sensor 2

Pro Tip
The meaning of the P0038 OBD2 Trouble Code is a mouthful, but basically the ECM (Engine Control Module) is detecting a problem in the heating circuit in O2 sensor #2.  This O2 sensor is located downstream in the exhaust system (after the catalytic converter).  This sensor monitors the oxygen content in the exhaust gases to help the ECM adjust the air-fuel mixture for optimal combustion.  If you are seeing the P0038 error code, this usually means you gotta wiring issue.

With that being said, the code refers to a fault or problem in the heating control circuits of the O2 sensor (HO2S). This code is closely related to P0037 which is an error caused by a low circuit. On the other hand, P0038 is a circuit high input code. Take note that most problems associated with high input codes are related to excessive voltages in the system or faulty alternators.

This is the reason why this DTC (Diagnostic Trouble Code) should be handled by a professional mechanic. In most cases, the check engine light is triggered by the O2 sensor due to short circuits in the vehicle charging system.

CarsNToys did a good video on troubleshooting this generic DTC on a 2010 Subaru:

What are the causes of P0038 code?

Most of the time, the problem has nothing to do with broken or faulty heated oxygen sensors. The P0038 code is most likely caused by faulty or burnt wiring, which has nothing to do with the sensor per se. Since the O2 sensor and related wiring are located close to the exhaust, it is not uncommon for the wiring to burn or wear out, most especially on older vehicles.

  • Burnt wires
  • Bad ground connections
  • Blown fuses
  • Faulty HO2S sensor
  • ECM issues
  • Certain types of exhaust leaks

Bad wiring and bad ground connections can cause a variety of short circuits in the system, which will also trigger the check engine light. And in some cases, blown fuses in the heater control circuit are the main causes of a P0038 trouble code.

P0038 fault code DTC explained

What are the symptoms of P0038 code?

The symptoms will vary wildly. Some vehicles will have a rich running condition while some may constantly run lean. The P0038 code also means reduced engine power and rough idling. It is not uncommon to see black smoke in the tailpipe along with the presence of a check engine light.

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DTCs like P0038, P0037, P0031 are often seen together when you’re having O2 sensor issues. You may see one or multiple at the same time.

  • Black exhaust smoke
  • Hard Start
  • Rough idling

Hard starting is also a common symptom of the DTC. But in the absence of engine and idling issues, the first thing you might notice is reduced fuel economy and a check engine light. If you notice problems with the exhaust system (such as unnecessary exhaust noise), it can also cause the P0038 OBD2 code to pop up after scanning the CPU.

How much does it cost to fix P0038 code?

It’s hard to say until a proper diagnosis is made. Since the P0038 OBD2 Trouble Code can be caused by many issues, the estimated cost to fix the problem will run anywhere from $70 to $200, but this all depends on the make and model of your vehicle AND whether or not you can do the repairs yourself.

The worst case scenario is replacing the O2 sensor, which will cost from $40 to $80 each (before including labor costs). You can expect to pay less if the check engine code is caused by a basic wiring issue.

Note: it is important to clear the trouble code from the vehicle’s ECM memory after repairs are made.  It is also a good idea to rescan with an OBD2 scanner periodically after a few driving cycles to make sure that everything is OK.


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