Water in Fuel - High Level
Indicates there is a high level of water detected in the fuel system.
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What it means (plain English)
The engine's computer is sensing too much water mixed with the fuel, which can cause poor combustion and rough running.
What the computer is actually seeing
The ECM monitors the fuel system for water contamination using a water detection sensor. When the sensor detects water concentration exceeding 0.1% by volume, it triggers SPN 1388.
What a healthy reading looks like
Fuel contamination should be less than 0.1% water volume for normal operation.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the fuel filter for signs of water. If water is present, replace the filter and drain the system before retesting.
- 22. Inspect the fuel system for leaks or sources of water ingress. Check seals and grommets in the fuel tank and lines.
- 33. Use a scanner to clear the code and run the engine. If the code returns, inspect the water detection sensor's connector and wiring for damage or corrosion.
- 44. Test the water detection sensor with a multimeter (2.5V to 3.5V is normal). If readings are out of range, replace the sensor.
Common causes
- Water ingress from bad fuel supply
- Damaged or faulty water sensor
- Fuel filter issues allowing water through
Typical repair cost
$$ - $$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It’s not recommended to drive; water in fuel can cause engine performance issues.
What happens if I don't fix this?
Ignoring it can lead to more severe engine problems, including damage to fuel injectors or a loss of power.
Why does this code often show with SPN 1387?
SPN 1387 is usually related to the low water level warning; both codes are linked to fuel water contamination issues.
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