P0451: EVAP System Pressure Sensor/Switch A Circuit Range/Performance
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - no effect on running.
Symptoms
- Check engine light only
- Emissions monitors not completing
- No symptom the driver can feel
Likely causes, most common first
- Fuel tank pressure sensor drifting
- Sensor contaminated by fuel
- Wiring or connector fault
- Blocked reference hose to the sensor
Read P0451 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0451 says the fuel tank pressure sensor is producing readings that are inside its electrical range but do not make sense - noisy, drifting, or not changing when the system is sealed. This is the sensor the whole leak test depends on, so a doubtful reading blocks the test rather than reporting a leak.
On many vehicles the sensor is mounted on top of the fuel tank or inside the pump module, which means dropping the tank to reach it. Confirm the diagnosis carefully before committing to that labour; watching the sensor's live value during a fill-up, when tank pressure genuinely changes, is a good test of whether it responds sensibly.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0451
“My 2014 mazda 6 EVAP system pops the p0451 when filling up gas to the first click. It goes away after a while if I take care to not fill up the tank all the way to the top. It is similar to a issue reported by recall 7414D for other 2014 mazda 6s. My car is not covered by the open recall, but it is experiencing similar issues. The p0451 goes on and off depending on how much i fill up the gastank.”2014 Mazda MAZDA6 · Aug 2025
“This has been an issue slowly getting worse over the last few months and escalated this week. June 20th, 2025 my car has literary died over (4) times during traffic and I had to try and stay calm while using a code reader to clear the codes to get the engine to start. Very scary, I have a 2017 Giulia Ti that just hit 100k miles. Even took it to the dealership and they couldn't explain it. Parasitic draw on my battery and they gave it a pass :( Codes: P2510-ECM/PCM POWER RELAY SENSE CKT RANGE/PERFORMANCE P0103-VAF CIRCUIT HIGH INPUT P0100- VAF CIRCUIT MALFUNCTION P0451-EVAP SYSTEM PRESSURE SENSOR/SWITCH 'A' RANGE/PERFORMANCE P0106-MANIFOLD ABSOLUTE PRESSURE/BAROMETRIC PRESSURE SENSOR CIRCUIT”2017 Alfa Romeo Giulia · Jun 2025
“Loss in fuel tank pressure. Structural stressing causing leaks at tank, fuel pump module connector and fuel supply hose. Dtc codes p0446 / p0451. Evap leak located in top tank port and associated direct connection secondary cracking of the plastic fuel supply line at tank top. Tank cracked at port. Cracking due to stress from normal driving vibrations as these ares are protected from road hazards.resulting gas leak will cover tank and metal shroud. Fire hazard from leaking gas.”2009 Chevrolet Silverado 2500 · Oct 2020 · 73,000 mi
Show 1 more owner reports
“Mil comes on intermittently with a p0451 (3-4 driving cycles after a cold start ) dtc, no obvious repair conditions present. Rough idle, power loss, hesitation, decrease in mileage. Issues go away on their own after pcm reset, come back shortly after mil sets again. Mil goes off randomly, and problems go away shortly after. Have run multiple diagnostics and no repair issues found. Was told the pcm itself might need to be replaced or reprogrammed.”2010 Ford Focus · Jan 2019
Cars that report P0451 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0451?
Yes - no effect on running.
How much does it cost to fix P0451?
Typical US repair costs range from $60 for the simplest fix (fuel tank pressure sensor) to $400 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0451. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.