P2264 indicates a malfunction in the water-in-fuel (WIF) sensor circuit, most commonly found on diesel engines. The WIF sensor sits inside the fuel filter or water separator and signals the PCM when water is present in the fuel; a circuit fault means the sensor's electrical signal is out of range, open, or shorted. It does not automatically mean the sensor is bad—the system may simply be detecting real water that has not been drained.
The single most common trigger. The sensor is doing its job; the fix is to drain the water separator and address how water entered the fuel (condensation, contaminated fuel source, etc.).
The sensor probe itself can fail internally from corrosion, age, or exposure to fuel additives, producing an out-of-range voltage that sets the code.
The WIF sensor lives in a harsh, moist environment near the fuel. Connector pins corrode, seals leak, and wires chafe, all of which create circuit faults.
A fuel filter that has absorbed too much water can keep the WIF sensor in a faulted state even after draining, and it should be replaced on schedule.
A high-resistance ground in the WIF circuit pulls the signal out of the expected range and triggers the code, even when the sensor and wiring look fine.
The engine control module is one of the least likely causes. It should only be considered after every other possibility has been ruled out by direct testing.
For short distances it is usually safe, but ignoring real water in the fuel on a diesel can cause injector damage, hydrolock, and expensive engine harm. Drain the separator promptly and complete the diagnosis rather than clearing the code and continuing.
On most diesel applications it is integrated into the bottom of the fuel filter housing or the fuel water separator, often just above the manual drain valve.
Not strictly required, but if the filter is old, restricted, or has clearly held a lot of water, replacing it at the same time is a common and sensible step because a saturated filter can retrigger the code.
Almost never. The PCM is one of the least likely causes of this code. In the vast majority of cases the actual problem is real water in the fuel, a failed WIF sensor, or corroded/damaged wiring and connectors. Replacing or reprogramming the PCM should only be considered after every other cause has been systematically tested and ruled out.