Testing Duramax Fuel Pressure Sensors: Step-By-Step Guide

Testing a Duramax LLY fuel pressure sensor involves the following steps:

1. Turn on the ignition with the engine off.

2. Use a scan tool to observe the actual fuel rail pressure parameter.

3. Check if the actual fuel rail pressure is within 1-1.8 MPa. If yes, the sensor is functioning normally. If no, proceed to the next step.

4. Disconnect the fuel rail pressure sensor.

5. Again, use a scan tool to observe the actual fuel rail pressure.

6. If the pressure is more than 175 MPa, replace the fuel rail pressure sensor. If not, test the fuel rail pressure sensor signal circuit for a short to the ground.

Turn on ignition with the engine off

To test a Duramax LLY fuel pressure sensor, start by turning on the ignition with the engine off. Observe the actual fuel rail pressure parameter with a scan tool and check if it is within 1-1.8 MPa. If it is, then the sensor is functioning normally. If not, proceed to the next steps.

Disconnect the fuel rail pressure sensor and once again, observe the actual fuel rail pressure with a scan tool. If the pressure is more than 175 MPa, then the sensor needs to be replaced. If the pressure is less than 175 MPa, then test the fuel rail pressure sensor signal circuit for a short to the ground.

Observe actual fuel rail pressure with a scan tool

To test a Duramax LLY fuel pressure sensor, you will need to observe the actual fuel rail pressure with a scan tool. Here is a step-by-step guide:

• Turn on the ignition with the engine off.
• Use a scan tool to observe the actual fuel rail pressure parameter.
• Check if the actual fuel rail pressure is within 1-1.8 MPa.

If the pressure is within the specified range, the sensor is functioning normally.

• If the actual fuel rail pressure is not within the specified range, proceed to the next steps.
• Disconnect the fuel rail pressure sensor.
• Once again, use a scan tool to observe the actual fuel rail pressure.
• Check if the actual fuel rail pressure is more than 175 MPa.

• If the pressure is above 175 MPa, replace the fuel rail pressure sensor.
• If the pressure is below 175 MPa, test the fuel rail pressure sensor signal circuit for a short to ground.

It is important to note that this procedure is based on information from online forums and may not be the only method to test the fuel pressure sensor. Always refer to the official repair manual or a certified mechanic for accurate and up-to-date information.

Disconnect the fuel rail pressure sensor and re-observe pressure

To test a Duramax LLY fuel pressure sensor, follow these steps:

• Turn on the ignition with the engine off.
• Observe the actual fuel rail pressure parameter with a scan tool.
• Check if the actual fuel rail pressure is within 1-1.8 MPa.
• If the pressure is within the specified range, the system is functioning normally.
• If the pressure is outside the specified range, proceed to the next step.
• Disconnect the fuel rail pressure sensor.
• Re-observe the actual fuel rail pressure with a scan tool.
• Check if the actual fuel rail pressure is more than 175 MPa.
• If the pressure is above 175 MPa, replace the fuel rail pressure sensor.
• If the pressure is below 175 MPa, test the fuel rail pressure sensor signal circuit for a short to ground.

It is important to note that some sources suggest that a reading of over 175 MPa indicates a good fuel rail pressure sensor, while others recommend replacing the sensor if the reading is above this value. Therefore, it may be advisable to consult a professional or refer to the vehicle's specific service manual for more accurate instructions.

Test the fuel rail pressure sensor signal circuit

To test the fuel rail pressure sensor signal circuit, follow these steps:

• Turn on the ignition with the engine off.
• Check if the actual fuel rail pressure is within 1-1.8 MPa. If yes, the operation is normal. If no, proceed to the next step.
• Disconnect the fuel rail pressure sensor.
• Re-check the actual fuel rail pressure with a scan tool. If the pressure is more than 175 MPa, replace the fuel rail pressure sensor. If not, proceed to the next step.
• Test the fuel rail pressure sensor signal circuit for a short to ground.

Check for air in the fuel system

To check for air in the fuel system, you can start by looking for some common signs of a leaking fuel filter housing. If your truck requires a lot of cranking to start after sitting for a few days, starts and then dies, or won't start unless manually primed when parked on an incline, you probably have a leaking fuel filter assembly.

There are several places where the fuel filter assembly could be leaking, including the O-ring seals at the top and bottom of the filter, the Water in Fuel sensor, or the filter head. The Water in Fuel sensor is a plastic component that screws into the bottom of the filter and can crack, especially as it gets older. The filter head has several small seals that can get dry and brittle and leak as the truck ages.

If you suspect a leak, the simplest fix is to replace the filter head, filter, and Water in Fuel sensor all at once. You can also check for external leaks by priming the fuel system and checking for fuel leaks. If the pressure drops quickly, this could indicate a leak. You can also install clear hoses at the inlet and outlet of the fuel filter housing to check for air in the lines.

Frequently asked questions