What it means
The DEF tank heater control circuit is open or has lost continuity — the PCM cannot drive the resistive heater that prevents the DEF (urea) tank from freezing in winter.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant tank heater warms the DEF tank so the fluid can thaw and remain usable in cold conditions. P202A sets when the heater control circuit is open or lacks continuity, preventing the control module from operating the heater as intended.
Common causes
Most likely first.
- Heater element winding open
- Open wire between PCM and heater
- Pin pushed back out of connector body
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Read freeze-frame data and reductant heater status, and check for DEF or NOx warnings and any start countdown.
- Inspect the tank-heater connector for a backed-out pin, corrosion, moisture, or damage from road debris.
- Check the heater harness for breaks or chafing between the tank and control circuit.
- With power isolated as specified by the manufacturer, measure heater-element continuity and compare it with the manufacturer's specification.
- If the heater and harness pass, test the control-side output and circuit continuity using the vehicle wiring diagram.
Common fixes
- Reconnect a loose heater plug or correctly seat a pushed-back terminal.
- Repair an open wire or damaged connector in the tank-heater circuit.
- Replace the reductant tank heater if its element is open.
- Repair the control-side circuit if it cannot operate a heater that passes testing.
Can I keep driving?
Drive only as needed while monitoring DEF and NOx warnings; in cold weather, an unheated tank may leave reductant unavailable and emissions controls ineffective. A displayed no-start countdown can eventually prevent restarting, so address the warning promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.