P0451Generic code

P0451 Code: Evaporative Emission Control System Pressure Sensor Range/Performance

The P0451 code indicates an implausible reading from the fuel tank pressure sensor in the EVAP system: electrically valid, but not what the computer expects. The main effect is that the EVAP leak test cannot run. Most of the time there are no other driving symptoms.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$40 to $300
Difficulty
Medium
System
Emissions Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0451 code means

The fuel tank pressure (FTP) sensor measures the pressure or vacuum inside the fuel tank. The computer uses it in the EVAP leak test: it creates a vacuum and watches how long it takes to bleed off.

The sensor gets a 5 V reference and a ground from the computer and sends back a signal between roughly 0.5 and 4.5 V. The P0451 code is a range fault. It means the sensor measures, but measures wrongly: wear, dirt, a clogged port or an abnormal real condition.

Without a reliable FTP reading, the computer cannot run the EVAP test. The monitor stays incomplete and the vehicle cannot pass an emissions inspection. Many FTP sensors share the 5 V reference with other sensors, so a reference fault can set several codes at once. Look up the sensor guide to see how it is tested.

This kind of fault is usually not solved with a multimeter, because electrically everything looks fine. You have to compare what the part says against reality: with a gauge, a thermometer, a vacuum pump, or by commanding the component with the scan tool and watching whether the physical result matches the command.

P0451 code symptoms

  • Check engine light on.
  • EVAP leak test cannot run.
  • Emissions monitor incomplete, so the vehicle cannot pass inspection.
  • Often there are no other driving symptoms.

Likely causes of the P0451 code

  1. Degraded or dirty sensor. It gives believable but wrong readings.
  2. Clogged port or hose on pressure sensors.
  3. Abnormal real condition: a leak, a blockage or a temperature outside the normal range.
  4. High resistance in the connector from corrosion.

How to diagnose the P0451 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check the reference and ground with the key on (5 V, and less than 0.1 V of voltage drop on the ground).
  4. Measure the signal with the connector plugged in and see whether it changes with conditions.
  5. Do a wiggle test on the wiring.
  6. Check continuity to the computer.
  7. Remove the gas cap and confirm the sensor reads atmospheric pressure (close to 0).
  8. Command the EVAP valves with the scan tool and see whether the reading changes.

How to fix the P0451 code

  • Repair the connector or the wiring.
  • Replace the sensor if the tests confirm it is bad.
  • Correct the real condition if there is one (a leak or a blockage).
  • Clear the codes and complete a drive cycle so the monitor runs.

Technical reference data

  • With the gas cap off: about 2.5 V on many sensors.
  • Vacuum: the voltage drops. Pressure: the voltage rises.
  • Approximate values only: check the manufacturer data for your engine.

Brand-specific notes

The location of the tank pressure sensor changes by manufacturer, so find it before you start testing.

P0451 on GM

On GM vehicles the sensor is mounted on the fuel pump module.

P0451 on Ford

On Ford vehicles the sensor is often next to the canister.

P0451 on Toyota

On Toyota vehicles the sensor is often next to the canister.

Frequently asked questions about P0451

Can I drive with a P0451 code?
Yes. A P0451 code usually carries no immediate risk. The problem is the emissions inspection.
Do I have to replace the sensor?
Only if the tests confirm it. The connector and the wiring fail just as often as the sensor.
Will I pass the inspection with this code?
No. The check engine light being on, or the monitor being incomplete, keeps the vehicle from passing.
How much does it cost to fix P0451?
Roughly $40 to $300, depending on whether it is a connector, a clogged port or the sensor itself.
What does the P0451 code mean?
It is a generic OBD2 code for a range or performance problem in the EVAP fuel tank pressure sensor. The sensor reads, but what it reads does not match what the computer expects.
What is the most common cause of P0451?
A degraded or dirty sensor, or a clogged port, giving believable but wrong readings. A real leak or blockage can also cause it.

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