P20BA: Diesel exhaust fluid heater not performing as expected
Reductant heater A control circuit performance
Severity: Severity not verified — if the car runs badly, have it inspected
Sources disagree: Carly rates P20BA as not serious, while CarParts.com says it is serious because the SCR system can be disabled and reduced power may follow.
P20BA in short
P20BA means the computer commanded the diesel exhaust fluid heater on and its response did not match what was expected. Causes include the heater, its temperature sensor or the wiring. Sources disagree on how serious it is, so get it checked soon, since the SCR system may be affected.
The heater keeps diesel exhaust fluid (DEF) from freezing so the SCR system can work in cold weather. TaT describes P20BA as a plausibility fault: the value is in the electrical range but does not match what should happen.
CarParts.com lists the heater, the reductant temperature sensor, wiring, the glow plug control module and, rarely, the PCM as causes.
Because the fault may stop the SCR system from working or stop DPF regeneration, it is worth a prompt check even though Carly rates it as not serious.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Reductant heater failed or performing badly
Common general cause- Why it ranks here
- CarParts.com lists the heater first, and TaT says the heater response did not match expectations.
- What would change this
- Rises if heater resistance or current is out of spec. Falls if the heater tests good.
Cause 2: Reductant temperature sensor faulty
Common general cause- Why it ranks here
- CarParts.com lists the temperature sensor; a wrong reading would make heater performance look bad.
- What would change this
- Rises if the sensor reading is stuck or implausible. Falls if it tracks ambient temperature.
Cause 3: Open or shorted wiring
Common general cause- Why it ranks here
- CarParts.com lists open or shorted circuits.
- What would change this
- Rises if the harness shows damage or resistance is off. Falls if wiring is fine.
Cause 4: Glow plug control module or PCM fault
Possible — needs testing- Why it ranks here
- CarParts.com lists the glow plug control module and rarely the PCM.
- What would change this
- Rises only after the heater, sensor and wiring pass.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all codes, including other SCR, DEF and DPF codes.
IfOther SCR or DEF codes are stored
It meansWork those together; they may share a cause.
IfOnly P20BA
It meansTest the heater circuit.
Step 2: Have a shop test the reductant heater, its temperature sensor and wiring with the vehicle repair manual.
Warning:The DEF and SCR system are near hot exhaust parts and DEF is corrosive. Leave this to a shop.
IfThe heater is out of spec
It meansReplace the heater.
IfThe sensor reads wrong
It meansReplace the sensor.
IfWiring is damaged
It meansRepair it.
Symptoms
- Check engine light
- DPF regeneration may not occur, which can lead to reduced power Gets more serious: stop and have it checked.
How to fix
Step 1: Note whether other DEF or SCR warnings appear and tell the shop.
On your vehicle
We don't have reviewed vehicle-specific evidence for P20BA yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P20BA yet.
P20BA questions
How serious is P20BA?
Sources disagree. Treat it as something to check soon, because the SCR system may be affected.
Sources and review
- P20BA Reductant Heater 'A' Control Circuit Performance
- P20BA Code: Reductant Heater A Control Circuit Performance
- P20BA fault code entry
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error