What it means
The reductant level sensor circuit signal is higher than expected. The code identifies a high circuit condition; the specific cause depends on the vehicle.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The DEF level sensor A sends a signal representing the amount of reductant in the tank. P203D sets when that signal rises above the control module's expected upper electrical limit, a high-circuit condition that differs from a low signal and can leave the displayed level incorrect.
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
- Record freeze-frame data and compare live sensor A level with the dashboard display and the actual DEF amount.
- Inspect the tank connector and harness for an open signal wire, loose or corroded pins, or insulation damaged near a power source.
- Check the sensor circuit supply, ground, and signal at the sender and control-module end against the manufacturer's specification.
- With power isolated as required, check for an open signal path or an unintended connection to battery voltage using the vehicle wiring diagram.
- If wiring and connector checks pass, test sensor A and replace it if its output remains above specification.
Common fixes
- Reconnect or clean loose and corroded sensor pins.
- Repair an open signal wire or wiring shorted to a power source.
- Replace a failed DEF level sensor A or sender assembly.
Can I keep driving?
Cautious driving is generally possible if the vehicle runs normally, but confirm the DEF level directly and arrange repair soon. The false level reading can trigger warnings or a start countdown, and emissions compliance may be affected.
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.