P223B: Reductant Heater F Control Circuit

P223B reports a fault in the control circuit of heater F, the sixth heating element of an SCR system. Like its neighbour P223A for heater E, it is a single catch-all code covering open lines and shorts alike. No maker documents P223B publicly, and the published systems show why: Ford's 2023 diesel summary names heaters A to C only (with A and B checked at peak heating power for under 3 A at more than 5 V), and GM bulletin 21-NA-149 lists the heater D codes P20C5 and P20C8 for the 3.0 L LM2 Duramax. Six zones would only appear on layouts with many separately heated lines or tanks. CARB requires every emission-relevant output to be checked for circuit faults. Expect an SCR warning and, in winter, the risk of a frozen line that ends in reduced power.

Symptoms

• Check engine light and SCR warning
• Reduced power warning after a cold-weather DEF fault

Most likely causes

• Damaged wiring or corroded connector of heater F
• Heating element F open or shorted
• Missing supply from the heater relay or fuse

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. Look for white crystals around the injector and the tank
3. Check connectors and heaters with the scanner
4. Run the dosing test available on your diagnostic tool
5. Replace parts only when the test points to that component

Good to know

• Repair difficulty: hard
• It can trigger limp mode.
• It affects emissions.

What each character of P223B means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• 3B: Specific fault in that system

Frequently asked questions

Can I keep driving with code P223B?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P223B?

The most common causes are: damaged wiring or corroded connector of heater F; heating element F open or shorted; missing supply from the heater relay or fuse.

Related codes

• P223AReductant Heater E Control Circuit
• P20C5Reductant Heater D Control Circuit/Open
• P20C1Reductant Heater C Control Circuit/Open
• P21C2Reductant Heater Relay Control Circuit/Open

Sources

• law.cornell.edu: 13 CCR 1968.2
• fordservicecontent.com: obd summary diesel 2023
• static.nhtsa.gov: MC 10205552 9999

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.