Checking Fuel Tank Pressure Sensors: A Step-By-Step Guide

The fuel tank pressure sensor is an important component of a car's evaporative emissions system, or EVAP. It monitors the pressure inside the fuel tank to detect leaks and faulty gas caps that might prevent fuel vapors from being contained. The data collected by the sensor is transmitted to the engine computer, which then alerts the driver of any issues by illuminating the check engine light. While a car may still run with a faulty FTP sensor, it is not advisable to drive for extended periods as it may result in increased emissions and potential environmental damage. Therefore, it is crucial to regularly check the fuel tank pressure sensor to ensure the proper functioning of the vehicle and compliance with emissions regulations.

Check the wires

To check the wires of a fuel tank pressure sensor, you will need a digital volt ohmmeter or a multimeter.

The fuel tank pressure sensor operates on a simple 3-wire circuit. The sensor has three wires: a ground wire, a wire that returns electricity to the powertrain control module (PCM), and a reference voltage wire that connects to the car's computer.

• Disconnect the connector to the fuel tank pressure sensor and turn on the ignition.
• Check for a voltage reading of 5 volts from the 5V grey wire to the ground (black wire) or a good frame ground.
• With the ignition on and the connector still disconnected, check for a very small amount of power (around 0.01V or similar) from the green signal wire to the black ground or a good body ground.
• If you don't get a reading, try grounding to a clean ground on the frame. If you now get power, the black ground wire may be broken somewhere.
• If you still don't get a reading, the grey wire may be broken.
• Repeat the same procedure for the green signal wire.
• These three wires are separate from the main harness and go directly from the ECM to the sensor.

If you find that any of the wires are broken, you may need to repair or replace them. It is important to note that accessing the fuel tank pressure sensor can be challenging as it is located inside or on top of the fuel tank. Most car owners will need to visit a mechanic to have the sensor and its wires examined.

Use an OBD2 scanner

Using an OBD2 scanner is a safe and easy way to check your fuel tank pressure sensor. Here's a step-by-step guide on how to do it:

Step 1: Start the Car

If your car can start, turn it on and let it run for a while to warm up the engine. This is important because cold engines can alter fuel pressure readings if there is an issue. Consider taking your car for a short drive of around 10 minutes to ensure the engine is warm.

Step 2: Connect the OBD2 Scanner

The next step is to connect your OBD2 scanner. Most modern vehicles have an OBD port located under the dashboard. You can use either a wired or wireless scanner. For wired scanners, simply plug the scanner into the OBD port. For wireless scanners, you'll need to connect it to an app on your smartphone or tablet.

Step 3: Check for OBD2 Trouble Codes

Once your scanner is connected, check for any stored fault codes in your vehicle's computer system, also known as the ECM (Engine Control Module). These codes will help identify any existing problems with the fuel system. Common OBD2 trouble codes related to the fuel system include:

• P0087/P0088: Rail Pressure Too Low/High, indicating an issue with the fuel pump, fuel filter, or fuel pressure regulator.
• P0171: System Too Lean, suggesting a problem with the fuel pressure, vacuum leak, or oxygen sensors.
• P0172: System Too Rich, indicating high fuel pressure, faulty fuel injectors, or a malfunctioning oxygen sensor.
• P0190: Fuel Rail Pressure Sensor Circuit Malfunction, suggesting a problem with the sensor, wiring, or fuel pressure.
• P0230: Fuel Pump Primary Circuit Malfunction, indicating an issue with the fuel pump relay, wiring, or the pump itself.

Step 4: Review Live Data

If no obvious problems are identified in Step 3, you'll need to review the live data. Navigate to the ECM control mode and scan it again. Then, go to the "Live Data" menu and select the "Fuel System" option. Here, you'll be able to monitor various parameters such as fuel pump, injection readings per cylinder, fuel pressure sensor, and rail pressure.

Compare the "specified" value (from the manufacturer) with the "actual" value (your current reading). If these values match, there is no problem in the chosen area. For a more accurate test, you can rev the engine to 2000 RPM and then to 3000 RPM, watching the values to see if they mismatch. Alternatively, you can take your vehicle for a short drive and record the live data to review later.

It's important to note that not all OBD2 scanners have live data reading and recording capabilities, so ensure you choose a scanner that supports these functions.

Test the fuel rail pressure sensor

Testing a fuel rail pressure sensor can be done at home with a multimeter. This sensor is a critical component of the fuel system of a car, monitoring the pressure of the fuel in the fuel injectors and facilitating the discovery of leaks. A defective sensor can cause a number of problems, including engine stalls, erratic running, and poor vehicle performance.

To test the fuel rail pressure sensor:

• Locate the fuel rail pressure sensor. It is usually found on the fuel injector rail.
• Disconnect the sensor electrical connector.
• Set the multimeter to the ohms setting.
• Place the multimeter probes on the sensor terminals. If there is no continuity, the sensor is faulty and needs to be replaced.
• Reconnect the sensor electrical connector.
• Start the engine and check for proper operation. If the sensor is not functioning correctly, the engine will run erratically or may not start.

If you suspect that your fuel rail pressure sensor is failing, it is important to have it checked by a professional as soon as possible. A failing sensor can cause a range of issues, and you may end up stranded with an engine that won't start.

Check for symptoms of a faulty sensor

The fuel tank pressure sensor is an integral part of your car's evaporative emissions system, also known as EVAP. It is placed atop or inside your fuel tank and monitors the pressure, both positive and negative, inside it. Here are some common symptoms of a faulty fuel tank pressure sensor:

• Illuminated Check Engine Light: When the sensor detects a problem, it sends a signal to the engine control module (ECM) or powertrain control module (PCM), which then illuminates the check engine light. However, this could also be due to other serious issues, so it's best to get it checked by a professional.
• Decreased Fuel Efficiency: A faulty sensor may fail to detect leaks, allowing fuel vapors to escape and decreasing fuel efficiency.
• Increased Emissions: A failing sensor can impact the evaporative emissions control system, leading to increased emissions of harmful pollutants.
• Hard Start: A faulty sensor can cause an incorrect air-fuel ratio, resulting in multiple attempts to start the engine.
• Strange Odors: Leaking fuel vapors can cause a strong fuel smell in and around your vehicle.
• Engine Stalling: A faulty sensor can cause the engine to stall due to an incorrect air-fuel mixture.
• Loss of Power: A compromised sensor can lead to a loss of power and acceleration.
• Rough Engine: The engine may run rough due to incorrect pressure readings affecting the air-fuel mixture.
• Black Smoke: Increased emissions and improper combustion can result in black smoke coming from the tailpipe.
• Gasoline Dripping: Leaks in the fuel system may cause gasoline to drip from the tailpipe.

If you notice any of these symptoms, it is important to consult a mechanic as soon as possible to diagnose and address the issue.

Consult a mechanic

If you suspect that your fuel tank pressure sensor is faulty, it is important to consult a professional mechanic to perform a thorough diagnosis and repair. Here are some reasons why you should seek the help of a mechanic:

Expertise and Experience

Mechanics have the necessary training, knowledge, and experience to accurately diagnose and repair fuel tank pressure sensor issues. They understand the complex workings of modern vehicles and can quickly identify the root cause of the problem.

Specialized Tools and Equipment

Diagnosing and repairing automotive issues often require specialized tools and diagnostic equipment. Mechanics have access to advanced tools, such as digital volt ohmmeters, OBDII scanners, and multimeters, which are typically not available to the average car owner.

Safety

Working with automotive electronics and fuel systems can be dangerous. Mechanics are trained to handle these systems safely and can prevent accidents or further damage to your vehicle.

Warranty and Guarantee

Reputable mechanics often provide warranties or guarantees for their work. This means that if the issue persists or something else goes wrong after the repair, you can take your car back to them without additional charges.

Time and Convenience

Repairing a fuel tank pressure sensor can be time-consuming, especially for those without the necessary expertise. Mechanics can efficiently diagnose and repair the issue, saving you time and allowing you to get back on the road sooner.

Comprehensive Inspection

When you take your car to a mechanic, they will not only address the fuel tank pressure sensor issue but also perform a comprehensive inspection of your vehicle. They can identify potential problems that may have otherwise gone unnoticed and provide you with a detailed report.

Compliance with Regulations

Fuel tank pressure sensors are crucial for maintaining compliance with state and federal emissions regulations. Mechanics will ensure that your vehicle meets the required standards, preventing you from incurring fines or penalties.

In conclusion, while it may be tempting to attempt a DIY repair, consulting a professional mechanic is the safest and most effective option when dealing with a faulty fuel tank pressure sensor. Their expertise, tools, and experience can help ensure a proper diagnosis, timely repair, and compliance with relevant regulations.

Frequently asked questions