What it means
DEF pressure sensor signal is unstable or jumps — usually a connector or chafed wire. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant pressure sensor reports DEF/AdBlue delivery pressure to the SCR control module. P204E sets when that signal jumps, drops out, or varies erratically instead of changing smoothly with pump operation, commonly because vibration or moisture interrupts the sensor connection or wiring.
Common causes
Most likely first.
- Intermittent connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
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 graph live pressure-sensor data during priming and while the fault is active to identify dropouts or sudden jumps.
- Inspect the sensor connector seal, pins, and harness routing for water ingress, loose terminals, chafing, or contact with a vibrating component.
- With live data displayed, gently move the connector and accessible harness sections to see whether the reading changes, taking care around hot exhaust parts.
- Check signal, reference, and ground circuits for intermittent continuity or voltage changes while moving the harness, using the manufacturer's test procedure.
- If the wiring remains stable, compare sensor output with actual DEF pressure during a prime to determine whether the sensor itself is erratic.
- Repair the intermittent fault and repeat the prime and drive conditions that originally triggered the code.
Common fixes
- Secure a loose connector and correct a damaged seal or poor terminal contact.
- Repair chafed wiring and reroute or secure the harness away from vibration or sharp edges.
- Replace the pressure sensor if its signal fluctuates while wiring and actual pressure remain stable.
- Clear the code and verify steady readings during priming and a drive cycle.
Can I keep driving?
A short trip may be possible if the vehicle runs normally, but get the intermittent fault checked soon and monitor SCR warnings. The signal may fail completely, impair reductant dosing, and lead to an emissions warning or eventual no-start countdown.
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.