What it means
Same as P238A with the signal voltage above the plausible range. 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
How it works
On diesel vehicles with a secondary water-in-fuel sensor, sensor B monitors water at its filter-housing stage. P238D means the control module sees sensor B’s signal above the plausible range, often because the signal is shorted to a supply or a wire has contacted a power source.
Common causes
Most likely first.
- Signal shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check-engine light on
- Water-in-fuel warning may be unavailable or inaccurate
How to diagnose it
- Save freeze-frame data and check scan-tool sensor B data for a reading stuck high while the fault is present.
- Locate the sensor B connector at the secondary filter housing using vehicle service information and inspect for corrosion, moisture, damaged pins, or a pinched harness.
- Trace the signal wire with the wiring diagram and check for a short to sensor supply or another power feed.
- Measure signal, supply, and ground circuits against the manufacturer’s specification and verify connector terminal contact.
- If the circuit passes, test sensor B using the manufacturer’s procedure.
Common fixes
- Repair a sensor B signal wire shorted to supply or another power feed.
- Clean and secure corroded or loose connector terminals.
- Repair a pinched or damaged harness and secure it away from power sources.
- Replace sensor B if it fails the manufacturer’s test.
Can I keep driving?
The water-in-fuel warning may be unavailable or inaccurate, so avoid extended driving until sensor B feedback is restored. If water goes undetected, it can damage the diesel high-pressure pump and injectors.
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.