CAT Engine 4604 Fault Code: Fuel Pressure Sensor - After Fuel Filter : Voltage Below Normal

What does CAT Engine error code 4604 mean?

Code 4604 relates to the fuel pressure sensor mounted after the fuel filter, which tells the ECM what pressure is available downstream of the filtration stage. The ECM uses this reading to judge filter condition and fuel delivery health, and to adjust fueling strategy accordingly.

This particular fault, Voltage Below Normal, means the signal wire coming back from that sensor is reading far lower than the ECM expects for a live sensor. The ECM continuously puts a pull-up voltage on the signal circuit so it can tell the difference between a sensor that is working, one that is open, and one that is shorted low. When that pull-up disappears or gets pulled to near zero, the ECM assumes a short circuit condition on the signal wire or inside the sensor itself.

Because the reading is invalid, the ECM logs the code, lights the warning lamp, and substitutes a default value for fuel filter outlet pressure so the engine can keep running, but without an accurate picture of actual filter or fuel system condition.

What triggers a CAT Engine 4604 code?

The ECM sets this code when the signal voltage from the secondary fuel filter outlet pressure sensor is less than 0.2 VDC for more than 8 seconds, and the ECM has been powered for at least 2 seconds. The warning lamp will illuminate and the code is logged, with the electronic service tool showing "Voltage Below Normal" on the status screen. The code will not go active if there are already active 262 codes or active 168 codes present.

Common causes of 4604

• Intermittent problem in the sensor circuit, sometimes caused by vibration or a loose connection that comes and goes
• Damaged connectors or wiring between the sensor and the ECM, including corrosion, chafing, or pinched wires
• A problem within the wiring harness itself, separate from the connector terminals
• A faulty fuel pressure sensor that has failed internally and is pulling its own signal circuit low
• A faulty ECM, which is possible but should be the last suspect after wiring and sensor are cleared

How to troubleshoot CAT Engine 4604: first checks

1. 1 Inspect the sensor connector at the fuel pressure sensor located after the fuel filter for corrosion, bent pins, moisture intrusion, or a loose fit
2. 2Trace the wiring harness from the sensor connector back to the ECM, checking for chafe points, pinched sections, or damaged insulation, especially near mounting points and moving components
3. 3Check that the sensor connector terminals are clean and making solid contact: supply voltage on terminal 1, sensor return on terminal 2, and sensor signal on terminal 3
4. 4With the key on and engine off, verify the ECM is providing its pull-up voltage on the signal circuit at the sensor connector to confirm the wiring back to the ECM is not open or shorted to ground
5. 5Check for other active codes, specifically 262 and 168, since either one active will prevent 4604 from going active and should be diagnosed first
6. 6If wiring and connectors check out, swap in a known-good sensor to isolate whether the sensor itself is faulty before condemning the ECM

How the code clears

No separate clearing step is listed beyond correcting the underlying wiring, connector, or sensor fault. Once the signal voltage returns to a normal operating range and stays there, the code should stop being active. Confirm with a diagnostic tool that the code is no longer active after the repair and clear any logged code per normal ECM procedures.

Affected models and serial ranges

4604 appears in our records across 6 CAT Engine models. Match your machine by model and serial number.