What Does the Engine Code P2238 Mean?

When your car shows the P2238 engine code, it means the voltage in your engine is too low.
Written by Kaitlin May
Reviewed by Melanie Reiff
If your car is displaying the engine code P2238, it means there’s a snag in the circuit system that maintains the right amount of voltage in your engine. This isn’t a cause for panic, but it’s an issue to address before it causes you to fail your emissions test.
Fixing a flat tire is one thing, but understanding the whys and hows behind diagnostic trouble codes (DTCs) like this one can help you differentiate between minor and major
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What does the engine code P2238 Mean?

Definition: O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 1
P2238 is a generic code for the engine control module (ECM) in any vehicle manufactured from 1996 onward, and it’s triggered when there’s a short circuit in the heater control circuit of the
O2 sensor
The ECM is the brain behind your engine. It manages the air-fuel ratio that keeps your car running safely. When the voltage detected by the ECM is outside of normal limits due to issues surrounding your O2 sensor, you’ll need to have it replaced.

How much does it cost to repair?

O2 sensor replacement
can cost anywhere between $75 and $150, and it takes about an hour to resolve. This will depend on your location, the
make and model of your vehicle
, and your engine type.

What can cause the P2238 engine code?

Some potential issues that could set off the P2238 engine code include: 
  • The front heated O2 sensor (Bank 1) is defective
  • The front heated O2 sensor (Bank 1) harness is open or has a short circuit
  • There’s a faulty electrical connection in the front heated O2 sensor (Bank 1)

Common symptoms of the P2238 engine code

An immediate warning sign that your O2 sensor is in trouble will be your
Check Engine Light
. Depending on your vehicle’s manufacturer, you’ll also notice drivability issues initiated by the ECM when it defaults to either failure mode or open loop fuel control.
There are different indicators for both operating systems. If your car shifts into failure mode fuel control, this is how you’ll know:
  • Your engine will be lazy in its acceleration
  • There will be stiffness in your throttle pedal
  • Additional warning signs (oil, battery, etc.) will be triggered
  • Your car won’t start at all
Open loop fuel control is another term for your engine throwing intuition to the wind and running on whatever levels of fuel and air are available. Heavy acceleration is a surefire sign that your engine has conceded to P2238, which can cause damage to your car in the long run.

How serious is the P2238 engine code?

If you don’t want to feel like your car has a mind of its own when it’s accelerating or decelerating at elevated levels, it’s best to get some eyes on code P2238 before more detrimental problems arise.
With the front heated O2 sensor circuit being shorted and the voltage too low, the ECM is left with no other option than to either place the engine in failure mode or open loop fuel control, and trust us—you don’t want to deal with either situation.
Not only is it not safe for you or your car, but it can also be the reason you fail an emissions test, which will keep you off the road anyway.

Can I fix the P2238 engine code myself?

If you’re hands-on when it comes to your
car repairs
, it’s possible to diagnose the issue by inspecting the relevant wiring harness and connectors. You can visually assess any damage, such as broken, bent, twisted, or corroded connector pins.

Common mistakes you can make

Without the help of a trained eye, though, there are some common mistakes that can trip up a P2238 diagnosis:
  • Clearing codes for the ECM before verifying the main failure using freeze frame data
  • Replacing the O2 sensor before the failure is confirmed
  • Failure to diagnose wiring short and replacing the O2 sensor instead

Tips for diagnosing the P2238 code

Since engines are more complex than ever, it’s a good idea to take your car to an experienced mechanic to verify the issue. 
These are the steps a mechanic will take to properly diagnose engine code P2238:
  • Run a scan for codes, record the current code in the ECM, and refer to the freeze frame data to identify the failure
  • Cross-reference the O2 heater sensor circuit and the other O2 sensors at the same voltage and input levels
  • Look for any open or short circuits in the O2 heater sensor circuit
  • Rule out a wiring issue to the power relay or ground with testing
  • Evaluate the wiring harness to identify circuit issues between the O2 sensor and the ECM

Replacing the O2 sensor

To replace the O2 sensor, follow these steps: 
  • Replace the O2 sensor when the heater circuit is shorted
  • Fix the wiring or connector pin for the O2 sensor
  • Replace the power relay if the testing pinpointed a damaged circuit
  • Replace the ECM entirely if it was damaged by the shorted circuit or sensor

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