Komatsu Excavator CA428 Fault Code: Water in Fuel Sensor High Error
Also called Water In Fuel Sensor High Error, Water-In-Fuel Sensor High Error, Water-In-Fuel Sensor High Error (Engine Controller System), Water-in-Fuel Sensor High Error, Water-in-fuel Sensor High Error
Water in Fuel Sensor High Error · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CA428 (also shown as user code E0E) is an electrical system fault on Komatsu PC200 and PC270 excavators. It sets when the engine controller sees high voltage in the signal circuit of the water-in-fuel sensor mounted on the fuel pre-filter. The engine keeps running with no controller action taken, but the water separator monitor on the dash will not display correctly.
Low severity. Komatsu lists no controller action for this code and the engine is not derated or shut down. The only confirmed effect is that the water separator monitor stops displaying correctly, so operators lose visibility into water buildup in the fuel pre-filter until the wiring or sensor is fixed.
What does Komatsu Excavator error code CA428 mean?
CA428 points to the water-in-fuel sensor circuit on the fuel pre-filter. This sensor is a simple ON/OFF style signal that tells the monitor when water has collected in the fuel filter bowl, so the operator knows to drain it before it reaches the injection system.
When the engine controller sees a high voltage reading on that signal circuit instead of the expected low/normal signal, it logs CA428 and flags the fault as an electrical system issue tied to the ENG controller.
Komatsu states plainly that there is no particular controller action taken for this code. The real-world impact is that the water separator monitor on the machine display will not show the correct status, meaning you could have water in the fuel and not get a proper warning.
Common causes of CA428
- Defective wiring harness connector at the sensor or controller end
- Defective water-in-fuel sensor installed on the fuel pre-filter
- Open circuit or short circuit in the wiring harness
- Open circuit in the wiring harness from wire breakage or poor connector contact
- Short circuit in the wiring harness, including short to another harness
- Defective engine controller
How to troubleshoot Komatsu Excavator CA428: first checks
- Turn the starting switch to the ON position, since this is the listed method to reproduce the failure code, and watch for CA428 to reset or reappear
- Use the monitoring function to check the ON/OFF signal from the water-in-fuel sensor under code 18800 (condition of WIF sensor) to see if the signal matches the actual condition of the fuel pre-filter
- Inspect the wiring harness connector at the water-in-fuel sensor for corrosion, looseness, or damaged pins
- Trace the harness between the sensor and the engine controller for chafing, pinched wire, or exposed conductors that could cause a short circuit or short to another harness
- Check for an open circuit caused by a broken wire or a connector that is not making good contact
- If wiring and connectors check out, test the water-in-fuel sensor itself, and suspect the engine controller only after the sensor and harness are confirmed good
How the code clears
No separate clearing procedure is listed for this code. Komatsu's documented method of reproducing the failure code is simply to turn the starting switch to the ON position, and diagnosis should proceed from the possible causes listed above until the high voltage condition on the signal circuit is resolved and no longer reproduces.
Affected models and serial ranges
CA428 appears in our records across 2 Komatsu Excavator models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| PC200 | Serial range not listed in source records |
| PC270 | Serial range not listed in source records |
Frequently asked questions
What does Komatsu code CA428 mean?
CA428 means the engine controller detected high voltage on the signal circuit of the water-in-fuel sensor mounted on the fuel pre-filter, on Komatsu PC200 and PC270 excavators. It is logged as an electrical system fault under the ENG controller.
Is CA428 a serious code that requires stopping the machine?
Komatsu lists no particular controller action for CA428, so the engine keeps running normally. The main consequence is that the water separator monitor will not display correctly, so it should be diagnosed but is not an emergency shutdown situation.
Will CA428 stop my excavator from starting or running?
No. Komatsu's documentation shows no controller action taken for this fault. It is a signal circuit problem affecting a monitor display, not an engine protection fault.
What is user code E0E on my Komatsu monitor?
E0E is the user-facing display code for CA428. It refers to the same water-in-fuel sensor high error on the fuel pre-filter.
How do I check the water-in-fuel sensor signal myself?
Use the machine's monitoring function and look up code 18800, which shows the condition (ON/OFF) of the water-in-fuel sensor. Compare that reading to the actual state of the fuel pre-filter.
What usually causes CA428 on a PC200 or PC270?
Common causes include a defective wiring harness connector, a bad water-in-fuel sensor, an open or short circuit in the harness (from wire breakage, poor connector contact, or a short to another harness), and less commonly a defective engine controller.
How do I reproduce CA428 for testing?
Komatsu's listed method is to turn the starting switch to the ON position and observe whether the code sets again, which helps confirm whether a repair has resolved the high voltage condition.