What it means
A general circuit fault on the secondary water-in-fuel sensor B - typically used on diesel systems with two filter housings (pre-pump and post-pump). The ECU loses water-detection feedback on this stage; risk of water reaching the high-pressure pump and injectors.
At a glance
- Usually lights the check-engine light
How it works
On diesel vehicles equipped with a secondary water-in-fuel sensor, sensor B monitors the relevant filter housing for water so the engine control module can warn the driver. P238A means the module detects a general electrical fault in sensor B’s circuit and may lose water-detection feedback at that stage.
Common causes
Most likely first.
- Water-in-fuel sensor B or its wiring fault
- Loose, corroded, or damaged connector
- Open or short in the sensor circuit
Symptoms
- Check-engine or water-in-fuel warning light on
- Possible reduced engine power
How to diagnose it
- Record freeze-frame data and check scan-tool status for the water-in-fuel warning and sensor B reading, if available.
- Identify the secondary filter housing and sensor B from vehicle service information, then inspect the connector for looseness, corrosion, moisture, or damage.
- Inspect the sensor B harness for cuts, chafing, pinched sections, and damaged connector seals.
- Use the wiring diagram to check sensor B’s signal, supply, and ground circuits for opens or shorts against the manufacturer’s specification.
- If wiring and connections pass, test sensor B and confirm the filter housing and sensor installation are correct.
Common fixes
- Reconnect and secure the sensor B connector.
- Clean corroded or contaminated terminals and restore damaged connector seals.
- Repair an open, shorted, or damaged sensor B wire.
- Replace sensor B if it fails the manufacturer’s test.
Can I keep driving?
Treat the water-in-fuel warning as unreliable while this fault is present, and avoid extended driving until the sensor B circuit is repaired. Water that goes undetected can damage the diesel fuel system, including the 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.