P238A is the general circuit code for water-in-fuel sensor B, used where a diesel has two water-detecting points, for example a frame-mounted primary filter and a second separator. Stellantis case file S2214000004 for 2022 Ram 2500 to 5500 trucks shows that on these vehicles the B sensor is part of the fuel filter mounted on the frame; P238A itself is not named there. No manufacturer documents P238A publicly. The sensor works like sensor A: two electrodes in the water sump read the conductivity. GM's 2018 diesel tables describe a self-test for sensor A in which a healthy probe briefly reports water right after power-up; a missing pulse counts as a circuit fault. While the code is stored, real water in the filter may go unnoticed, so drain the separator regularly.
Low severity. Can I keep driving?You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.
Symptoms
- Water-in-fuel lamp or message on
- No warning for real water in the chassis filter
Most likely causes
- Water or corrosion in the sensor B connector at the chassis filter
- Damaged harness along the frame rail
- Water-in-fuel sensor B failed
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: easy
What each character of P238A means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 3: Ignition and misfires
- 8A: Specific fault in that system
Frequently asked questions
Can I keep driving with code P238A?
You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.
What causes code P238A?
The most common causes are: water or corrosion in the sensor B connector at the chassis filter; damaged harness along the frame rail; water-in-fuel sensor B failed.
Related codes
- P238BWater in Fuel Sensor B Circuit Range/Performance
- P238CWater in Fuel Sensor B Circuit Low
- P238DWater in Fuel Sensor B Circuit High
- P238EWater in Fuel Sensor B Circuit Intermittent
- P238FWater in Fuel Condition - Sensor B
- P2264Water in Fuel Sensor A Circuit
Sources
- static.nhtsa.gov: MC 10229750 9999
- gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
- en.wikipedia.org: Water in fuel sensor
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.