What it means
The reductant quality sensor signal is above the expected level. This code alone does not identify an open signal or short to B+ as the cause.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant quality sensor reports urea concentration in diesel exhaust fluid (DEF), also called AdBlue, to the emissions control system. P206D sets when its signal is higher than the expected range; an open signal line or short to battery voltage is possible, but the code alone does not identify the cause.
Common causes
Most likely first.
- Open signal line
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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
- Review freeze-frame data and live quality readings to confirm the signal is high, and note any related reductant or NOx codes.
- Check the DEF type and tank condition, but do not treat a high electrical reading alone as proof that the fluid is too concentrated.
- Inspect the quality sensor connector for corrosion, loose or backed-out pins, and check the harness for damage or contact with a power source.
- Use the wiring diagram to test for an open signal wire and for an unintended short to battery voltage.
- If the circuit is intact, verify the sensor’s supply, ground, and output against the manufacturer’s specification.
Common fixes
- Secure loose connector pins or repair poor contact at the quality sensor.
- Repair an open signal wire or a damaged harness section.
- Repair wiring shorted to a power source and protect it from rubbing or pinching.
- Replace the quality sensor if its output remains high with a verified sound circuit.
Can I keep driving?
The vehicle may drive normally at first, but the emissions system can show a DEF warning and may begin a no-start countdown if the fault continues. Arrange diagnosis promptly and follow any countdown or restart warnings.
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.