P20BA Reductant Heater A Control Circuit Performance

OBD-II DTC Datasheet

Reductant Heater Control Circuit Performance A

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code and applies to many OBD-II diesel vehicles (1996 and newer). This may include, but is not limited to, Ford, Mercedes Benz, Sprinter, Audi, Ram, Chevrolet, Dodge, BMW, GMC, etc. Despite the general nature, the exact repair steps may vary depending on the model year, brand , transmission models and configurations. ...

A stored P20BA code means that the powertrain control module (PCM) has detected an abnormal voltage that is outside the normal range of expected values on the control circuit for the onboard reductant heater, indicated by the letter A. This designation is used when multiple reductant heaters are in use, refer to manual vehicle repair to determine which A circuit is right for your application.

The catalyst system is responsible for reducing (mostly) all other exhaust emissions, although some applications are also equipped with a NOx trap.

Exhaust Gas Recirculation (EGR) systems take another step in reducing NOx emissions. However, today's larger, more powerful diesel engines cannot meet strict federal (US) emission standards with just an EGR system, a particulate filter / catalytic converter, and a NOx trap. For this reason, selective catalytic reduction (SCR) systems have been invented.

SCR systems inject a reducing agent compound or Diesel Exhaust Fluid (DEF) into the exhaust gases upstream of the particulate filter and / or catalytic converter. The precisely calculated DEF injection raises the temperature of the filter element and allows it to work more efficiently. This extends the service life of the filter element and helps reduce emissions of harmful exhaust gases into the atmosphere.

The entire SCS system is monitored and controlled by either the PCM or a stand-alone controller (which interacts with the PCM). In any case, the controller monitors the O2, NOx and exhaust gas temperature sensors (as well as other inputs) to determine the appropriate timing for the DEF (reductant) injection. Precision DEF injection is required to keep the exhaust gas temperature within acceptable parameters and to optimize the filtration of pollutants.

Reducing agent heaters are used to prevent diesel engine exhaust fluid from freezing at extreme temperatures. These heaters are usually located in the DEF reservoir and / or in the supply hose (s) of the reducing agent nozzle.

If the PCM detects an abnormal voltage that is outside the normal range of expected values on the control circuit for reductant heater A, a P20BA code will be stored and the malfunction indicator lamp may illuminate.

Reducing agent heaters can be located inside the DEF tank (example shown here):

What is the severity of this DTC?

The saved P20BA code should be treated as serious and should be resolved as soon as possible. The SCR system could be disabled because of this. Catalyst damage can occur if the conditions that contributed to the code persistence are not corrected in a timely manner.

What are some of the symptoms of the code?

Symptoms of a P20BA DTC may include:

Reduced engine performance
Excessive black smoke from vehicle exhaust
Decreased fuel efficiency
Other codes related to SCR

What are some of the common causes for the code?

Reasons for this code may include:

Poor reductant heater
Open or short circuit in the reducing agent heater control circuit
Reducing agent temperature sensor defective
Bad SCR / PCM controller or programming error

What are some steps to troubleshoot the P20BA?

To diagnose the P20BA code, you will need access to a diagnostic scanner, digital volt / ohmmeter (DVOM), and vehicle-specific source of diagnostic information.

If you can find a Technical Service Bulletin (TSB) corresponding to the year of manufacture, make and model of the vehicle; as well as engine displacement, stored code / codes and symptoms detected, it can provide useful diagnostic information.

You should begin your diagnosis by visually inspecting the harnesses and connectors of the reductant heater system. Burnt or damaged wiring and / or connectors must be repaired or replaced before proceeding.

Then connect the scanner to the vehicle diagnostic socket and retrieve all stored codes and corresponding freeze frame data. Make a note of this information before clearing codes and test driving the vehicle until the PCM enters ready mode or the code is reset.

The code is intermittent and can be much harder to diagnose (currently) if the PCM goes into ready mode. In this case, the conditions that contributed to the retention of the code may need to worsen before an accurate diagnosis can be made.

If the code resets, search your vehicle information source for diagnostic block diagrams, connector pinouts, connector face views, and component test procedures and specifications. You will need this information to complete the next step in your diagnosis.

Use DVOM to check the power supply of the SCR / control system. Check fuses with a loaded circuit to avoid misdiagnosis. If appropriate power (battery voltage) and ground circuits are found, use the scanner to activate the reductant heater / s and check the control circuit output voltage. If the voltage is insufficient, suspect the controller is defective or has a programming error.

If the output voltage circuit is within specifications, use the DVOM to test the reducing agent heating element in question. If the heater does not meet the manufacturer's specifications, it is suspected that it has failed.

If this code is exposed in warm weather, suspect that a programming error has occurred.

Related DTC discussions

Code P20BA for Ford F450 DieselThis code was showing up in warm weather on my F450 with cab and chassis 6.7 diesel 2013. I read that it could be a programming error if it happens in warm weather. How can I find out about this without being at the mercy of the dealership. Thanks Stewart ...
2015 F-350 6.7 Diesel with code P20BAFord Dealership advises that Diesel Exhaust Pump Delivery Unit on Diesel F2015 350 6.7 Years must be replaced with engine light code P20BA; does this make sense to anyone? ...

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