What is Detroit Diesel SPN 164 FMI 20 and How to Fix It?

If you own or operate a Detroit Diesel engine, you may encounter a fault code that reads SPN 164 FMI 20. This code indicates a problem with the fuel rail pressure sensor or the quantity control valve. In this article, we will explain what this code means, what causes it, and how to troubleshoot and fix it.

What is SPN 164 FMI 20?

SPN stands for Suspect Parameter Number, and FMI stands for Failure Mode Identifier. These codes are used to identify and diagnose faults in electronic control systems. SPN 164 refers to the fuel rail pressure sensor, which measures the pressure of the fuel in the common rail. FMI 20 means that the sensor signal is drifting high, meaning that it is reading higher than the actual pressure.

This code can cause the engine to derate by 25%, meaning that it will lose power and performance. It can also trigger the malfunction indicator lamp (MIL) and the check engine light (CEL) on the dashboard.

What causes SPN 164 FMI 20?

There are two possible causes for SPN 164 FMI 20:

  • The fuel rail pressure sensor is faulty or damaged. This can happen due to wear and tear, corrosion, contamination, or physical damage. A faulty sensor can send inaccurate or erratic signals to the engine control module (ECM), which can result in incorrect fuel injection and combustion.
  • The quantity control valve is faulty or damaged. This valve is located on the high-pressure pump and regulates the amount of fuel that enters the common rail. A faulty valve can cause the fuel pressure to fluctuate or deviate from the desired level, which can affect the engine performance and emissions.

How to troubleshoot and fix SPN 164 FMI 20?

To troubleshoot and fix SPN 164 FMI 20, you will need a diagnostic tool that can read and clear fault codes, such as the Detroit Diesel Diagnostic Link (DDDL). You will also need a multimeter, a fuel pressure gauge, and a repair manual for your specific engine model. Here are the steps to follow:

  1. Connect the diagnostic tool to the diagnostic port and read the fault code. Verify that it is SPN 164 FMI 20 and that it is active or stored. If it is inactive or not present, the problem may be intermittent or resolved. Clear the code and monitor the engine for any recurrence.
  2. Turn the key on and the engine off. Check the wiring and connectors of the fuel rail pressure sensor and the quantity control valve. Look for any signs of damage, corrosion, loose connections, or short circuits. Repair or replace any faulty components as needed.
  3. Measure the resistance of the fuel rail pressure sensor and the quantity control valve using the multimeter. Compare the readings with the specifications in the repair manual. If the resistance is out of range, replace the sensor or the valve as needed.
  4. Measure the fuel pressure in the common rail using the fuel pressure gauge. Compare the reading with the specification in the repair manual. If the pressure is too high or too low, check the fuel supply system for any leaks, restrictions, or air intrusion. Repair or replace any faulty components as needed.
  5. Start the engine and monitor the fuel pressure and the sensor signal using the diagnostic tool. If the pressure and the signal are stable and within the normal range, the problem is fixed. If the pressure or the signal is still erratic or high, replace the fuel rail pressure sensor or the quantity control valve as needed.
  6. Clear the fault code and test drive the vehicle to verify that the engine is running normally and that the code does not reappear.
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