P20BD — Reductant Heater B Control Circuit/Open — 6.7 Powerstroke
Diagnostic reference for P20BD on 6.7 Powerstroke (2011–present).
What it means
The PCM has detected an open or fault in the DEF (reductant) heater B control circuit.1
Most likely causes
- Open or high-resistance in the Reductant Heater B control circuit wiring/connectors. — Inspect the heater B control wiring and connectors for opens, corrosion, or damage; check continuity to the PCM and the heater element. Cold-weather operation makes this fault more likely.1
- Failed or intermittent DEF heater relay/fuse in the heated DEF circuit. — Verify the DEF heater relay and associated fuse for proper operation and supply voltage; a failed relay or blown fuse will set an open-circuit condition for Heater B.1
- Faulty Reductant Heater B element or internal open. — Check the heater B element resistance and its connection at the DEF tank/line assembly; an internal open in the heater mimics a control-circuit open.1
How to diagnose
- Confirm the code with a scan tool and note freeze-frame conditions; cold ambient temperature increases likelihood.
- Visually inspect DEF heater B wiring, connectors, and routing for chafing, corrosion, or moisture intrusion; repair as needed.
- Check the DEF heater relay and fuse for proper operation and supply voltage; replace if faulty.
- Measure resistance/continuity of the Reductant Heater B control circuit from PCM to heater and verify heater element resistance to spec; isolate wiring vs heater fault.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| DEF urea concentration | 32.5% (check with a DEF refractometer) | Sample from the tank | Ram service bulletin 25-005-14 (Diesel Exhaust Fluid) |
| DEF freeze point | About 12°F (−11°C); freezing alone is normal and the system is built to thaw it | Cold weather | Ram service bulletin 25-005-14 (Diesel Exhaust Fluid) |
Parts and tools you may need
- Digital multimeter
- Scan tool with live data/freeze frame
- Wiring diagram for 6.7 Powerstroke DEF heater circuit
- Basic hand tools for connector access
Tools you’ll need
- OBD-II scan tool — Confirms P20BD and retrieves freeze-frame data to correlate with cold ambient conditions.
- Digital multimeter — Measures resistance/continuity of the Reductant Heater B control circuit and heater element to isolate wiring vs heater faults.
- Automotive test light — Quickly verifies supply voltage and relay/fuse operation in the heated DEF circuit.
- Inspection mirror and flashlight — Allows visual inspection of DEF heater B wiring, connectors, and routing for chafing, corrosion, or moisture intrusion.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| ECM/PCM software update | — | 0.5–1.5 hrs | Shop |
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| DEF tank heater / heated line | $100–$1,200 | 1–3 hrs | DIY with tools and a manual |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
When to see a pro
If wiring faults persist after inspection, or if PCM driver suspicion remains, have a qualified diesel technician perform pinpoint tests and repairs. Do not service high-pressure fuel injection systems without proper training and safety equipment.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Repair videos: P20BD on the 6.7 Power Stroke
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 6.7 Powerstroke? This goes straight to the editor — it is not published.