CAT Engine 187 Fault Code: Fuel Control Valve : Not Responding Properly
Fuel Control Valve : Not Responding Properly · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 187 (SPN 18 / FMI 7) on the C175 engine means the fuel control valve on the high-pressure fuel pump is not moving to the position the ECM is commanding. The actual fuel actuator position does not match the desired position within specifications. This affects fuel pressure regulation and engine performance, so it should be diagnosed before continuing normal operation.
High severity. This code points to a mismatch between the commanded and actual fuel actuator position, which controls fuel pressure on a high-pressure common rail system. Left unaddressed, it can cause poor engine performance, stalling, or damage to the fuel control valve or pump. It is not usually an immediate stop-now emergency, but it should be diagnosed the same shift it appears.
What does CAT Engine error code 187 mean?
This code applies to the C175 engine's high-pressure common rail fuel system. Fuel pressure is generated by a high-pressure fuel pump, and a fuel control valve on that pump regulates how much fuel enters it, which controls the fuel pressure the system produces.
The fuel control valve is a mechanical valve with its own electrical actuator and controller. The engine ECM sends a desired throttle position to this controller using a PWM signal at a constant frequency of 500 Hz. The duty cycle of that signal changes with engine load and speed: approximately 10 percent at low engine idle, approximately 20 to 25 percent at high engine idle with no load, and approximately 50 to 60 percent at high engine idle under full load.
Code 187 sets when the actual position of the fuel actuator does not match the desired position within specifications. In other words, the ECM is asking the valve to move to a certain point, but the valve is not getting there or is not reporting that it got there. This can stem from wiring problems, a bad power supply to the controller, a CAN data link issue, or a failing fuel control valve itself.
Common causes of 187
- Problem with the wiring harness or a connector in the fuel control valve circuit
- Supply voltage to the controller not at 14.0 ± 1.5 VDC
- Problem with wiring for the CAN data link
- Keyswitch power not reaching the fuel control valve controller
- Supply voltage not reaching the controller
- Power module not generating the correct voltage
- Problem with the battery circuit for the power module
- Problem with the circuit that supplies battery voltage to the power module
- Problem with the fuel control valve itself
- ECM not generating the correct PWM signal for the controller
How to troubleshoot CAT Engine 187: first checks
- Check the condition of every connection at the connectors in the fuel control valve circuit. Confirm connectors are clean, dry, and tightly sealed. An intermittent connection in the harness or a connector is a common cause of this code.
- Use Cat Electronic Technician (ET) to view the Fuel Actuator Position Command parameter and compare it against expected values: approximately 10 to 15 percent at low engine idle, approximately 20 to 25 percent at high engine idle with no load, and approximately 40 to 50 percent at high engine idle with full load.
- Verify supply voltage to the fuel control valve controller. The power module should convert battery voltage (24 VDC) down to 14.0 ± 1.5 VDC for the controller. Check for a blown 15 amp fuse for the power module located in the cab of the machine.
- Inspect the battery circuit and the circuit that supplies battery voltage to the power module for damage, loose connections, or corrosion.
- Check wiring for the CAN data link, since the desired throttle position is also communicated via the CAN data link as a throttle backup control.
- If connectors, wiring, and supply voltage all check out, the fuel control valve itself may need to be replaced.
How the code clears
No separate clearing step is listed. After checking and correcting connector, wiring, and supply voltage issues, the guidance is to replace the fuel control valve if the problem is not resolved.
Affected models and serial ranges
187 appears in our records across 1 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C175 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 187 mean?
It means the fuel control valve on the high-pressure fuel pump is not reaching the fuel actuator position that the ECM is commanding. The actual position and desired position of the fuel actuator are not within specifications.
What system does code 187 affect?
It affects the high-pressure common rail fuel system on the C175 engine, specifically the fuel control valve that regulates how much fuel enters the high-pressure fuel pump, which controls fuel pressure.
Can I keep operating the machine with code 187 active?
This code signals a fuel pressure regulation problem, which can affect engine performance and, if ignored, risk further damage to the fuel control valve or pump. It should be diagnosed promptly rather than run indefinitely.
What voltage should the fuel control valve controller be getting?
The power module should supply 14.0 ± 1.5 VDC to the controller, converted down from battery voltage of 24 VDC. There is also a 15 amp fuse for the power module located in the cab of the machine that should be checked.
How do I check if the fuel actuator is responding correctly?
Use Cat Electronic Technician (ET) to view the Fuel Actuator Position Command parameter. At low engine idle it should read approximately 10 to 15 percent, at high engine idle with no load approximately 20 to 25 percent, and at high engine idle under full load approximately 40 to 50 percent.
Does code 187 mean I need to replace the fuel control valve?
Not necessarily right away. First check all connectors for clean, dry, tight connections, inspect wiring and supply voltage, and check the CAN data link wiring. If the problem is not resolved after those checks, the fuel control valve should be replaced.
Is code 187 related to a wiring problem or a hardware failure?
It can be either. Causes range from a loose or corroded connector, harness damage, and CAN data link wiring issues to power module or battery circuit problems, or a genuinely failed fuel control valve or ECM PWM output.