What Does the Engine Code P2BAB Mean?

Engine code P2BAB means your vehicle is emitting excessive NOx.
Written by David Ghanizadeh-Khoob
Reviewed by Melanie Reiff
The presence of engine code P2BAB means that your vehicle is emitting too much nitrous oxide. This is typically caused by an issue in the selective catalytic reduction system. Usually, the code doesn’t pose any dangerous driving conditions, but it will hinder the performance of your engine.
Diagnostic trouble codes (DTCs) are generated by the onboard diagnostics (OBD) system to identify engines issues. If you have an OBD-II reader, or if you have recently had your computer read, it’s important to know what the codes actually represent.
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What does the engine code P2BAB mean?

Definition: NOx exceedance – incorrect exhaust gas recirculation (EGR) flow
Diesel engines have a selective catalytic reduction system that reduces the emissions of oxides of nitrogen (NOx) released from the exhaust. This works by injecting a small amount of reductant into the exhaust gas stream entering the diesel particulate filter. The reductant reacts with NOx to produce nitrogen, oxygen, and water vapor.
The engine control module (ECM) uses sensors upstream and downstream of the diesel particulate filter (DPF) to measure NOx emissions. One sensor is located at the outlet of the engine, the other is located in the DPF measuring emissions exiting the filter.
If excessive NOx emissions are present, the code P2BAB will be set and the ECM will deactivate other systems to prevent any additional damage.
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How much will it cost to fix?

If you don’t have an OBD-II reader, then it will take about one hour of labor to a P2BAB engine code. Most mechanics charge between $75 and $150 per hour.
The cost to repair the issue will vary substantially depending on what is causing the issue. For example, the cost of replacing a NOx sensor is typically between $250 and $350, but if you have to replace the DPF, then the repair could easily cost thousands of dollars.

What can cause the engine code P2BAB?

Dysfunction in any component of the catalytic reduction system can cause engine code P2BAB. Some common causes include:
  • Faulty NOx sensors
  • NOx sensors harness open or shorted
  • Poor electrical connection in the NOx sensor circuit
  • A blockage in the EGR system
  • EGR valve
  • Faulty diesel particulate filter
  • Incorrect or insufficient DPF or NOx recovery fluid
  • A faulty PCM

Common symptoms associated with engine code P2BAB

If the P2BAB engine code is set, your
check engine light
or “service engine soon” light will turn on.
It is common for people to not experience any other obvious signs or symptoms. Sometimes you can notice black smoke being emitted from your exhaust during acceleration, reduced fuel efficiency, or a decrease in engine power.

How serious is the engine code P2BAB?

If you read a P2BAB engine code, you can probably continue to drive your car safely. However, the performance of your engine will be compromised. Also, your car will most likely fail an emissions test.
As a result, it is recommended to resolve the underlying issue as soon as possible.
MORE: How to pass emissions testing

Can I fix the issue myself?

The ease of repair of a P2BAB engine code will depend heavily on the cause. It is crucial to get an accurate diagnosis if you intend to try to do the repair yourself.
Here are some steps to take on the road to solving the problem:
  1. Check for any other OSB-II codes. The excess NOx could be related to another issue that needs to be resolved first
  2. Clear the error codes, drive the vehicle, and see if it reappears
  3. Check your vehicles technical service bulletins (TSB)
  4. Make sure there is sufficient DPF and NOx recovery fluid, and ensure it is the correct type of fluid for your vehicle
  5. Test the O2 sensors and the catalyst
  6. Check for any damage to the wiring, harnesses, connectors, or components
  7. Fix any issues you find
  8. If you don’t find any issues, try replacing the ECM
Troubleshooting and solving the underlying cause of a P2BAB engine code can be a tricky process, so it is recommended to employ a professional to help with the process.
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