Like all OBD-II trouble codes, P0451 has the same meaning for all vehicles. It means that your Acura RL‘s EVAP system has a pressure sensor that is malfunctioning in some way.
P0451 is usually caused by either a bad EVAP pressure sensor, a clogged fuel tank relief valve, EVAP lines, EVAP wiring, or a bad fuel cap. There can be other causes as well. We’ll cover those directly below.
P0451 is usually caused by either a bad EVAP pressure sensor, a clogged fuel tank relief valve, EVAP lines, EVAP wiring, or a bad fuel cap….
RL P0451 Symptoms
Typically, P0451 will not affect the way that your RL runs or drives. Fuel mileage may suffer a bit, and certainly the service engine soon light will come one. You may also notice the slight smell of gas.
If there are other EVAP related trouble codes, concentrate on them first and see if it helps remedy this one.
P0451 Causes: Acura RL
Here are some of the most common causes of P0451 in general.
Bad/Missing Fuel Cap
The easiest place to start diagnosing P0451 is to take a look at the fuel cap. Since a missing, bad, or under-tightened fuel cap can make your RL throw this code it’s a great place to start.
If you’ve gotten a “tighten fuel cap” message recently, but the cap was already tight, that’s a strong indication that there could be something wrong with the fuel cap.
Fuel caps have a rubber seal around them where they make contact with the fuel receiver. Make sure that this seal is not dry rotted or missing. If it is, a new gas cap may be exactly what you need to fix the problem. That being said, the fuel cap is often misdiagnosed as the cause of P0451.
EVAP Lines and Wiring
The next place to look for what could be causing P0451 in your RL is the EVAP system lines and hoses. Pay attention to anywhere that they connect to something else, go near the exhaust, or touch anything that could slowly cut through them.
Checking the wiring harness would be follow the same principal. You would be looking to see if it has been damaged in any way. Pay particular attention to where it plugs into the EVAP pressure sensor. If the plug is loose or looks damaged, it may be time to replace that part of the harness.
The carbon canister could also be bad.
Bad EVAP Pressure Sensor
Now would be a great time to check the fuel pressure sensor signal. You’ll need a good scanner. You’ll want to test to see if it is within the specs that Acura requires before getting a new one. Here’s a fantastic video on how to do just that:
Fuel Tank Pressure Relief Valve
If everything else checks out, I would consider doing a smoke test before checking the fuel tank pressure relief valve. They are typically a challenge to get to. Here’s a link to a great video on how to track down a leak if you don’t have a smoke machine.
Conclusion: P0451 Acura RL
P0451 can be a challenging trouble code to track down. The good news is that if that’s the only code that your RL has, it shouldn’t really be a breakdown risk.
If there is anything that you would like to add, please feel free to leave a comment below. Good luck!