P20B9 on 2011-2025 Chevrolet Silverado 3500HD — Reductant Heater "A" Control Circuit/Open
1 vehicles · 1 makes · $300-$2,500 repair
Most Reported On
P20B9 is an OBD-II diagnostic trouble code meaning “Reductant Heater "A" Control Circuit/Open.” This code applies to diesel vehicles with Selective Catalytic Reduction (SCR) and means the engine computer detected an open circuit in the control for reductant (Diesel Exhaust Fluid / DEF) heater "A". This heater keeps the DEF and its lines from freezing or crystallizing in cold weather so the emissions system can function. An open control circuit means the heater can't be commanded properly, which can cause DEF freezing, SCR faults, and eventually reduced power or limited engine starts to enforce emissions compliance. It should be addressed promptly, especially in cold climates. This code is most commonly reported on 2011-2025 Chevrolet Silverado 3500HD, with repair costs ranging from $300 to $2,500.
Common Causes
Typical Repair Cost
Based on 1 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P20B9, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
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BlueDriver Pro Bluetooth Scanner
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Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
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- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
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A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
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Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
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FAQ
What does P20B9 mean?
P20B9 stands for "Reductant Heater "A" Control Circuit/Open." This code applies to diesel vehicles with Selective Catalytic Reduction (SCR) and means the engine computer detected an open circuit in the control for reductant (Diesel Exhaust Fluid / DEF) heater "A". This heater keeps the DEF and its lines from freezing or crystallizing in cold weather so the emissions system can function. An open control circuit means the heater can't be commanded properly, which can cause DEF freezing, SCR faults, and eventually reduced power or limited engine starts to enforce emissions compliance. It should be addressed promptly, especially in cold climates.
What are the most common causes of P20B9?
The most common causes of P20B9 are: Open or broken wiring in the reductant heater circuit, Corroded or loose heater connector, Failed reductant (DEF) tank heater element, Blown fuse or relay for the heater circuit, Faulty DEF heater control module, PCM driver circuit fault (rare). The specific cause varies by vehicle.
How much does it cost to fix P20B9?
Repair costs for P20B9 range from $300 to $2,500, depending on the vehicle and root cause.
Which vehicles are affected by P20B9?
Au7o has documented P20B9 across 1 vehicle models from 1 manufacturers: Chevrolet.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.