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P20BA Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P20BA is an OBD-II Code that refers to Reductant Heater A Control Circuit Performance


A P20BA code is a generic diagnostic trouble code (DTC) which means that the powertrain control module (PCM) has detected improper voltage that is outside the normal parameters within the control circuit for the on-board reductant heater assigned the letter A.

During cold weather, diesel exhaust fluid is kept from freezing by reductant heaters. Depending on the manufacturer, they may be near the DEF reservoir or the reductant injector supply line/s. If the PCM detects a voltage in the control circuit for reductant heater A that is outside of normal expected range, a code P20BA will be stored and a malfunction indicator lamp light up.


Common causes for this code include:

  • Bad Reductant Heater
  • Reductant Heater circuit poor electrical connection
  • Reductant Heater harness is open or shorted
  • Faulty SCR controller/PCM or programming error (rare)


The symptoms of a P20BA code are:

  • Other SCR related codes
  • Vehicle exhaust has excessive black smoke
  • Engine performance has decreased.
  • Fuel efficiency is reduced


To diagnose a P20BA DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data.
  2. Check for external influences.
  3. Poor connection in the reductant heater supply line/s or DEF reservoir
  4. Condition of SCR controller/PCM and freeze frame data. 
  5. If the code was set at a certain temperature and reset, freeze frame data would indicate that it was cold outside when the code was set. This would help the technician to diagnose the problem.
  6. Using a DVOM, check for resistance on the heater supply line/s and look for continuity across the connector pins.
  7. If there is poor connection in either supply line/connector or if reductant heater supply line/s is leaking, replace as necessary and clear codes.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P20BA code:

  • Not checking the freeze frame data to determine the conditions under which the DTC was set.
  • Not checking the documents for the vehicle to ensure that the code is correct and not a different code.
  • Using diagnosis equipment that does not properly interpret the DTCs and advise them of their scan results.
  • Not performing all tests

How serious is this?

A P20BA code is considered to be a serious problem. If left too long this can be very expensive to repair and may include replacing several components that are very expensive such as the catalytic converter. 

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Repair poor connections to reductant heater supply line/s
  • Replace SCR controller/PCM if problem persists.
  • Add more fluid to the DEF reservoir if needed.
  • Remove any access reductant hoses and warranty hoses, clean them out thoroughly before reinstalling new hoses.

Related codes

A P20BA is related to and may be accompanied by the following codes:

P20BB – Reductant Heater Control Circuit Low

P20BC – Reductant Heater Control Circuit High

U0193 – SCR System Fault Condition

U1091 – Common Rail Pressure Control Valve Range/Performance Problem 

U1090 – Common Rail Pressure Control Valve Electrical Problem


In conclusion, the P20BA code is a diagnostic trouble code that refers to the control circuit for reductant heater A. This code is considered to be serious and has a number of possible causes. It can also mean that there are vehicle exhaust issues, poor SCR performance or an expensive catalytic converter replacement is needed. Due to the nature of this problem, it should not be ignored since doing so may cause further damage to the vehicle.