P20B9: Diesel exhaust fluid heater circuit open
Reductant heater A control circuit open
Severity: Inspect soon
KBB calls the code serious: the SCR system may become disabled and frozen fluid can damage the tank in winter.
It gets more serious if:
- Stop: Avoid driving in freezing weather until it is repaired.
P20B9 in short
P20B9 means the computer sees an open circuit in the heater that keeps diesel exhaust fluid from freezing. A failed heater, damaged wiring or a poor connection are the usual causes. Kelley Blue Book says warm-weather driving is possible but winter driving risks damage from frozen fluid.
The reductant heater warms the diesel exhaust fluid in cold weather so the SCR emissions system can work.
P20B9 sets when the computer gets no voltage from the heater control circuit.
KBB says causes include the heater element, wiring, a temperature sensor or the controller, and the SCR system may be disabled.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Failed reductant heater element
Common general cause- Why it ranks here
- Both sources list the heater first.
- What would change this
- Rises if the heater tests open. Falls if it tests normal.
Cause 2: Open or shorted harness, or poor connection
Common general cause- Why it ranks here
- Both sources list wiring and connections.
- What would change this
- Rises if damage or corrosion is found. Falls if wiring tests good.
Cause 3: Temperature sensor, SCR controller or PCM
Possible — needs testing- Why it ranks here
- KBB lists these after heater and wiring.
- What would change this
- Rises if heater and wiring test good. Falls if either fails.
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 and freeze-frame data and note other SCR codes.
IfOther SCR or DEF codes present
It meansDiagnose together.
IfP20B9 alone
It meansInspect the heater circuit.
Step 2: Have the heater and harness inspected for corrosion, damage, opens and shorts.
Warning:The DEF system and exhaust are near hot parts and chemicals. Let a shop do it.
IfHeater is open
It meansHeater failure.
IfHarness open or shorted
It meansWiring fault.
IfBoth good
It meansSensor or controller.
Symptoms
- Check engine light
- Reduced performance or SCR warning Gets more serious: stop and have it checked.
How to fix
On your vehicle
FordYour car
2016–2020 · F-150
Supported by vehicle dataFord bulletin TSB 21-2336 names P20B9 (also listed for f-250, f-350). Some F-150 3.0L diesel, Super Duty 6.7L and F-650/F-750 trucks set a long list of codes that includes P20B9. Only the summary was read, so the repair is not stated here. Whether it is still current is not verified.
TSB 21-2336Status unverified
MIL on with several DEF and emissions codes including P20B9 (3.0L and 6.7L diesels)
2016–2020f-150, f-250, f-350 · issued · NHTSA 10201907
Some F-150 3.0L diesel, Super Duty 6.7L and F-650/F-750 trucks set a long list of codes that includes P20B9. Only the summary was read, so the repair is not stated here.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
No curated relationships for P20B9 yet.
P20B9 questions
Can I drive with P20B9?
KBB says you can in warm weather, but avoid winter driving since frozen fluid can damage the tank.
Sources and review
- P20B9 error code
- P20B9 OBD error code summary
- Ford TSB 21-2336: MIL on with several DEF and emissions codes including P20B9 (3.0L and 6.7L diesels)
- 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