P238B

Code

Generic P — Powertrain

Water in Fuel Sensor B Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 20 EN: 27 RU: 20

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Page language: EN

Causes

Failed or degraded water-in-fuel (WIF) sensor B
Corroded, loose or contaminated connector at the sensor
Damaged wiring (open, short to ground or battery, high resistance)
Water or contaminants in the fuel/water separator or filter
Poor sensor ground or missing reference voltage
Intermittent connector contact caused by vibration or corrosion

Symptoms

Malfunction Indicator Lamp (MIL) or water-in-fuel warning illuminated
Possible fuel system limp mode or derate on some vehicles
Poor starting or rough running if fuel delivery or sensor function is affected
Service messages indicating water in fuel or filter service required
Intermittent faults related to moisture or vibration

What to check

Retrieve freeze frame and live data with a scan tool; confirm P238B and note conditions when set
Visually inspect WIF sensor B, its connector, and wiring for corrosion, damage, or loose pins
Inspect fuel/water separator and primary fuel filter for presence of water or contamination; drain per service procedure if present
Check for related codes (other WIF sensors, fuel pressure, ECM communication)
Verify proper reference voltage (typically ~5V) and good ground at the sensor connector
Measure sensor signal voltage or resistance with key on/engine off and while cranking if applicable

Signal parameters

Sensor type: typically resistive or switched/resistive element that changes with water contact
Reference voltage: commonly ~5 V supply from PCM (verify vehicle spec)
Signal output: typically a 0–5 V or resistance change; expected in-spec idle value should be stable and within vehicle manufacturer limits
Open circuit or erratic voltage swings indicate wiring/connector issue or failed sensor
When water is present the sensor's electrical characteristic changes (consult vehicle data for expected values)

Diagnostic algorithm

Use a scan tool to confirm P238B, check freeze frame and any stored related codes. Note when code sets (key on, running, after rain, after filter change).
Visually inspect the sensor B area, connector and wiring for corrosion, water intrusion, chafing or damage. Repair obvious problems and clear codes to retest.
If fuel/water separator or filter contains water, drain/replace following safe manufacturer procedure; clear codes and retest.
Backprobe the sensor connector (or remove and measure per service manual) with key on to verify reference voltage, signal voltage and ground presence. Compare to service specifications.
Measure sensor resistance if applicable (cold, dry state) and while introducing known test condition per manual. Replace sensor if out of spec.
If wiring checks show high resistance or opens/shorts, repair harness using proper splices, terminals and seals. Recheck for DTCs after repair.
If sensor and wiring test good but code returns, check PCM inputs and grounds at the module. Consider module-level faults only after ruling out sensor/harness.
After repairs, clear codes and perform road test or repeated ignition cycles to confirm the fault does not return.

Likely causes

Sensor B element contaminated with water or diesel/contaminants
Connector corrosion causing high resistance or intermittent signal
Wiring short to ground or open in the harness to sensor B
Failed sensor electronics producing out‑of‑range voltage/resistance
Fuel filter/separator saturated with water allowing continuous sensor activation

Fault status

⚠️ Status

PCM detected Water-in-Fuel Sensor B output outside expected range/performance. Condition may be caused by sensor fault, contaminated fuel/filter, wiring/connectors or PCM input issue. Repair should begin with inspection of sensor, filter/separator and connector, followed by electrical testing.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours