Scan Tool Fuel Pressure Check: How To Do It Right

Scan tools have become the most important instrument for diagnosing fuel supply problems. They can verify if the modules controlling the fuel pump are receiving the correct data, such as oil pressure, crank position, and security information. Late-model vehicles have returnless fuel systems, which vary the speed of the pump to meet fuel requirements. This means that if you connect your voltmeter to the fuel pump circuit, the readings will fluctuate. To monitor fuel pressure, a scope is required to graph the amperage and voltage. The most common customer complaints regarding fuel pumps are no-start conditions, intermittent no-start conditions, and hard starting. After performing a visual inspection of the vehicle and verifying the customer's complaint, a scan tool can be connected to pull codes and ensure that the modules are communicating on their buses. This information can then be used to develop diagnostic strategies and further tests to resolve the issue.

Check the fuel pump with a scan tool

The first step in diagnosing fuel pump issues is to perform a visual inspection of the vehicle. Next, verify the customer’s complaint by ensuring that the vehicle will not start and run.

After the initial inspection, you can connect a scan tool to pull codes and ensure the modules are communicating on their buses. Some low-end generic tools may not be compatible with all modules, so an enhanced or factory scan tool is recommended. These enhanced scan tools can perform a “health check” and pull codes and parameters from the modules with a single click. They can also automatically test and bi-directionally control components to confirm operation.

With the codes pulled, you can develop diagnostic strategies and further tests to resolve the no-start condition. Service information is critical and can be used to determine the set of parameters that must be met for the pump to be energized. For some systems, this may include a crank sensor signal, oil pressure, and a check with the vehicle theft deterrent module.

If the vehicle has any “loss of communication” codes that start with a “U”, these should be resolved before diagnosing or replacing the fuel pump. While these codes may seem unrelated, a dead module or short in the serial bus can often result in a no-start condition.

For port fuel injection systems and gasoline direct injection (GDI) systems, pressure sensors can be observed with a scan tool. For GDI-equipped Asian and European models, there are no ports to attach a gauge, so a scan tool is necessary to observe pressure.

Factory and enhanced scan tools can monitor pressure transducers on the high and low sides of the system. This information can be used to diagnose the health of the low-side and high-side pumps. These tools will have the PID parameters for these components as part of the Mode 6 data, which can indicate the pressures during different modes of operation.

By using a scan tool, you can verify if the modules controlling the fuel pump are receiving the correct data, such as oil pressure, crank position, and security information. On late-model imports, the fuel pump may have its own module or node on the serial data bus, allowing it to share data like the fuel level and tank pressure with other modules.

With a scan tool, you can monitor this data and check if the serial data bus is unable to communicate with certain modules, which could cause the fuel pump to shut down.

Verify the customer's complaint

This is a crucial step that should not be overlooked. Many diagnoses go wrong because the technician fails to verify the customer’s concern. If the customer says the vehicle does not run, make sure it will not start and run.

At this stage, forget about using your "noid" lights. This low-cost tool is useful for simple vehicles, but it can be misleading when dealing with modern vehicles. If the vehicle has Gasoline Direct Injection (GDI), you won't even be able to access the injectors to install a noid light. If you want to prove that the injectors are pulsing, try using a scope and amp clamp instead.

After the visual inspection and verifying the customer’s complaint, you can move on to connecting the scan tool. First, pull the codes and ensure that the modules are communicating on their communication buses. Some low-end generic tools may not be compatible with all modules, so you might need an enhanced or factory scan tool for this step.

These enhanced or factory scan tools often have a "health check" feature that can pull codes and parameters from the vehicle's modules with just one click or press of a button. Some even have automated tests that can bi-directionally control components to automatically confirm their operation.

With the codes pulled, you can start formulating diagnostic strategies and planning further tests to resolve the issue, such as the no-start condition. Remember that service information is just as critical as a pressure gauge in the diagnostic process.

Connect the scan tool and pull codes

To connect the scan tool and pull codes, follow these steps:

First, locate the Data Link Connector (DLC), also known as the OBD2 port. This is usually found under the steering column or, in most passenger vehicles, on the driver's side of the car on the underside of the dashboard. Once located, connect your scan tool to the OBD2 port.

Next, turn the ignition to the 'ON' or 'IDLE' position. This step is necessary for the scan tool to establish communication with the vehicle's computer. The scan tool will then automatically pick up the vehicle's VIN and connect to the vehicle's computer to read and display diagnostic trouble codes (DTCs).

After the scan tool has successfully established communication, the check engine diagnostic trouble codes will be displayed on the scan tool's screen. These codes are listed in order of severity and will provide a description of what they mean. You can use the UP or DOWN buttons on the scan tool to navigate through the codes if more than one is present.

Additionally, you can press the 'System Status' button on the left side of the scan tool to access further diagnostic trouble code options. Use the UP or DOWN buttons to navigate through the selections, then press 'ENTER' to continue.

Once you have finished viewing the check engine codes and other diagnostic information, you can safely remove the scan tool by turning the ignition off and disconnecting the wired connection from the OBD2 port. The scan tool will store the vehicle data in its memory.

Check the vehicle's theft deterrent module

Checking the vehicle's theft deterrent module is an important step in diagnosing fuel pump issues. Here's a detailed guide on how to check the vehicle's theft deterrent module:

The theft deterrent module is a crucial component of your vehicle's security system, designed to deter the theft of your vehicle, gas, and wheels. It also helps protect against break-ins through broken windows, providing an extra layer of security. To ensure the effectiveness of this system, it is essential to arm the advanced theft deterrent feature. Here's how you can do it:

• Locking the Vehicle: Arm the system by locking your vehicle using the key fob, Keyless Access System, or the interior door lock. When using the interior lock, make sure to push the power lock switch or button while the door is open. The system won't arm if you use the interior door lock switch when the door is closed or locked with a key.
• Arming the System: After locking, the advanced theft deterrent system will be armed. This enables features like the Electric Fuel Filler Lock, which locks the fuel door to prevent siphoning, and the Steering Column Lock, which prevents the vehicle from being driven, towed, or pushed away without an authorized key fob.
• Understanding the Sensors: The Vehicle Inclination Sensor, Interior Movement Sensor, and Glass Breakage Sensors work together to protect your vehicle. The inclination sensor detects changes in the tilt of the vehicle, such as when it's jacked up or towed. The interior movement sensor uses ultrasonic waves to detect movement or unauthorized entry. Glass breakage sensors, located in the rear quarter panel and lift gate windows, detect broken glass and protect valuables in the cargo area.
• Activating the Alarm: If any of the sensors are triggered, the vehicle alarm will activate. This will set off the horn, siren, and vehicle lights, and if equipped, the Surround Vision Recorder will also be activated. Additionally, the Shielded, Battery-Backed Alarm Siren will sound if there is an abrupt loss of signal from the Body Control Module.
• Disabling Sensors: If needed, you can disable the Inclination and Interior Movement Sensors. With the vehicle turned off, locate the ALARM DISABLE button, which looks like a vehicle with a line drawn through it, usually on the overhead console. Pressing this button momentarily disables these sensors for the next alarm system-arming cycle.

Remember to always refer to your vehicle's owner's manual for specific instructions and information regarding the advanced theft deterrent system and its features.

Monitor pressure transducers on high and low sides of the system

Factory and enhanced scan tools can monitor pressure transducers on the high and low sides of the fuel system. This information can be used to diagnose the health of the low-side and high-side pumps. These tools will have the PID parameters for these components as part of the Mode 6 data. These parameters can tell you what the pressures should be during the different modes of operation.

The high-pressure fuel pump is mechanical and is typically driven by a camshaft. A lobe on the camshaft pushes on a follower or roller that moves a piston. The piston in the pump has two cycles, suction, and compression. The solenoid on the side of the pump controls how much fuel is compressed during the compression stroke. During the suction cycle, the solenoid will allow fuel from the low-pressure side of the fuel system to enter the pump. As the piston starts to travel upwards, the solenoid will remain open. The fuel is pushed into the low-pressure side of the fuel system when the solenoid is open. When the solenoid is shut, the low-pressure and high-pressure sides of the fuel system are isolated.

If there is low demand on the engine, the solenoid will remain open longer and a smaller volume of fuel is compressed. If there is a high demand for the engine, the solenoid will close sooner, and a higher volume of fuel will be compressed. The length of time the solenoid is open will determine how much fuel reaches the fuel injectors.

The in-tank pump in GDI systems is more responsible for volume than pressure. Fuel on this side of the system is called the low-pressure side. A fuel pump on the engine pressurizes the fuel for high-pressure injectors. This pump is driven off a lobe on the camshaft. This part of the fuel system is called the high-pressure side.

Frequently asked questions