Error Code P1093 is defined as Fuel Rail Pressure Too Low.

This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles makes. Rather, it applies only to specific vehicle makes, such as Isuzu, Chevrolet, BMW, Volkswagen/Audi, and Subaru. Specification of the definition, troubleshooting, and repairs still vary from one make and model to another.


Error Code P1093 is set because the fuel rail pressure is low. Meaning, there’s a problem in the fuel pressure relief valve. This is quite a common problem among diesel engines.

The valve is a small plug at the end of the driver’s side fuel rail. When this valve gets hot, the start to open is a bit too soon and will set this code.

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. In some cases, the vehicle may lose power

Possible Causes

Many factors may contribute to this code, such as:

  • Clogged fuel filter
  • Leakage in fuel system
  • Defective fuel injector
  • Defective fuel pump
  • Defective FRP (fuel rail pressure) sensor

How to Check

Technicians usually start their diagnosis of this code by checking the fuel filter. If the fuel filter is clogged, then it must be cleaned or replaced.

Then, technicians will proceed to check leakage in the fuel system.

Then, they will check the fuel injector and fuel pump, before checking the fuel rail pressure sensor if it’s working properly, or receiving the correct voltage.

How to Fix

Since a blocked fuel filter is the common cause of this problem, then cleaning or replacing your fuel filter can fix the problem. Other repairs, of course, include repairing or replacing components to prevent fuel system leakage.

  • Replacement of fuel injector
  • Replacement of fuel pump
  • Replacement of FRP

For some vehicle makes and models, such as Chevrolet Duramax, a simple and quick solution can be done with the use of a shim that will hold the pressure back.