P20BA – Reductant heater control A – circuit performance problem

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By Randy Worner (Contact Me)
Last Updated 2016-08-26
ASE/ACA World Class Technician
CodeFault LocationProbable Cause
P20BA Reductant heater control A - circuit performance problem
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Wiring, reductant heater, ECM

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Table of Contents

  1. What Does Code P20BA Mean?
  2. What are the common causes of code P20BA?
  3. What are the symptoms of code P20BA?
  4. How do you troubleshoot code P20BA?
  5. Codes Related to P20BA
  6. Get Help with P20BA

What Does Code P20BA Mean?

Reductant heater

The reductant heater control system is used by the Powertrain Control Module (PCM) to heat up the Diesel Exhaust Fluid (DEF) to prevent it from freezing. Diesel exhaust fluid is sprayed inside the catalytic converter to reduce NOx emissions. There are 2 different heating systems at work here; one is for the DEF Supply Line and the second is for the DEF Tank Heater. This code is aimed at the DEF Supply Line Heater. The DEF Tank Heater is usually part of the DEF Supply Pump Assembly although some manufacturers may have them as separate units.

A control unit/module is responsible for operating the DEF system heaters. Manufacturers will differ on which control unit or module this is. This unit determines how much DEF is sprayed into the exhaust based upon input from the PCM. It also determines when the heaters are turned on for both the tank and for the supply line. In either heater’s case, as the temperature of the DEF falls below the 32 degree mark, the PCM will have the control module operate the various DEF system heaters. Anytime there is a problem in the heating system, the DEF control unit/module reports this to the PCM. The PCM sets the applicable trouble code in memory and turns on the Malfunction Indicator Light (MIL). Once the DEF control unit/module can operate the heater again within 3 consecutive key cycles, the PCM will turn off the MIL and the code will become stored.

Code P20BA will set when the either the power or ground circuit voltage is too low or too high when it should not be, or the heater does not operate within the time frame specified by the manufacturer.

What are the common causes of code P20BA?

  • Faulty connections at the DEF control unit/module/DEF Supply Line Heater – given its location and the environment it lives in – likely.
  • Failed DEF Supply Line Heater – shorted – possible
  • Failed PCM –highly unlikely

What are the symptoms of code P20BA?

  • Malfunction Indicator Light “ON”
  • Reduced Engine Power
  • Message Center / Instrument Cluster displaying Engine Power Is Reduced

How do you troubleshoot code P20BA?

First, take a look and see if there are any technical service bulletins (TSB) for your particular vehicle. There may be an update, or known fix put out by the manufacturer that can save you from wasting time and money.

Next, see if there are any other diagnostic fault codes. Diagnose current faults first, in the order in which they are stored. Misdiagnosis occurs when this code is diagnosed when it is a stored code, especially while other codes are active. Also, check for active DEF Tank Heater and DEF Supply Pump fault codes. If these codes are present, diagnose them before attempting to diagnose the P20BA.

If the P20BA is the only active fault code present, and there are no updates/TSBs for your particular vehicle, then the next step is to locate the DEF Supply Line Heater, which is close to the DEF Supply Pump on the DEF tank. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burn spots or melted plastic. Pull the connectors apart and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt or possibly green in color versus the normal metal color you are probably used to seeing. You can get some electrical contact cleaner at any parts store if cleaning of the terminals is needed and a light plastic bristle brush to clean them with. Afterwards let them air dry, get some dielectric grease and put some where the terminals come into contact.

If you have a scan tool that is capable of running an Actuator Test or a Relay Test, you will need to operate the DEF Line Heater Relay. Once you have done that, clear codes and see if the P20BA code returns. If it does not, then the connections were most likely your problem.

If the P20BA code does return, we will need to test the heater and its associated circuits. Typically, there are 2 wires at the DEF Supply Line Heater.

For this code, the easiest thing to do unplug the DEF Supply Line Heater connector. With the scan tool hooked up, see if code P20B9 DEF Supply Line Heater Circuit High Input is now active after 15 seconds. If this happens, then the wiring, DEF control unit/module and PCM are good. The most likely problem is the DEF Supply Line Heater.

If the P20BA code stays active and the P20B9 does not set, we will need to test the heater’s associated circuits. At this point it may be wise to seek assistance from a trained automotive diagnostician. And remember, PCMs must be programmed, or calibrated to the vehicle in order to be installed correctly.


P20B9 Reductant Heater A Control – Circuit Open – voltage on these circuits are high/open.

P20BB Reductant Heater A Control – Circuit Low – voltage on these circuits are low/grounded.

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