Reductant Heater 'A' Control Circuit Low
The reductant heater is not functioning correctly, affecting emissions control.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The car has a heater to warm up the diesel exhaust fluid (DEF) but it's not getting enough power, making it take too long for the fluid to work properly in colder temperatures.
What the computer is actually seeing
ECM notices that the voltage at the reductant heater is below expected levels, usually under 5 volts when it should be around 12 volts when activated.
What a healthy reading looks like
Expected voltage at the reductant heater should be around 12V when activated, and resistance is typically between 5-15 ohms for the heater element.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the fuse for the reductant heater circuit. Replace if blown.
- 22. Inspect wiring and connectors for damage or corrosion. Repair or replace as needed.
- 33. Measure voltage at the reductant heater connector with the engine running. Should be around 12V. If not, check the power supply and ground connection to the heater.
- 44. Check the resistance of the heater element. Should be between 5-15 ohms. If outside this range, replace the heater.
Common causes
- Open circuit in the reductant heater wiring
- Faulty reductant heater element
- Damaged connector or loose wiring
- Fused blown for the reductant heater circuit
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally drivable, but be aware that emissions may be affected, and it might not perform well in cold conditions.
Will the code come back after clearing?
If the underlying issue isn't fixed, the code is likely to return.
Why does this code appear with others like P20C1?
Codes like P20C1 often indicate similar issues with the reductant heater, so they're seen together frequently.
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