P0456 CEL Troubleshooting

Hey Guys,

I am trying to figure out a P0456 CEL code on my 2003 Tacoma 2.7L. My scanner referred to it as a "Evaporative Emission System Leak Detected (very small leak)." I scanned my truck using OBD Fusion on my iPhone and my Veepeak OBDCheck BLE scanner.

So in April 2019, I had the same code on my truck. I ended up replacing the vacuum line that connects from the air filter box to the hard line near the radiator, and that solved the problem.

I am not sure where to look next with this issue, or if I should clear the code and see if it resurfaces again (I've see that the gas cap is sometimes the cause...?)

I've got a 600+ mile trip next week, plus state inspection so I wanted to resolve this before both of those.

Any thoughts?

Thanks,
Tom

 

sorry for the long explanation.

depending on your scan tool and the availability of information available to you you might have to find a good smog shop. what you are looking for is Mode 6 data. Mode 6 data is the actual data that the PCM gets from its continuous testing of the systems on the truck. Emissions testing done by the PCM programming is broken into 2 main parts, 2 trip tests and semi-instant or one trip tests. Evaporative tests are 2 trip tests. I say semi-instant for the following reason. Take an engine miss for example. The PCM has to sense that that cylinder or multiple cylinders have mis-fired a certain number of times before the CEL (check engine light) illuminates. This might take 1 second, or 1 minute depending on other factors.

Not knowing what you know or dont know, please accept my apologies if I am telling you things you already know. All OBDII vehicles (since 1996) have what is called a drive cycle. The moment you start the motor, the drive cycle starts and the PCM goes through its tests. Depending on what test it is performing and if it passes or fails a CEL may or may not be illuminated. Like I said before, evap tests are 2 trip tests... a bad or missing gas cap should take 2 trips to set the CEL. Does your gas cap "whoosh" when you take it off to fill the tank? There should be some pressure unless the vent solenoid or the evap canister has recently purged.

If your scanner can get Mode 6 data, it may or may not give you data that you can understand. The more expensive scanners, $1k and up, will give Mode 6 data in English as opposed to a PID$ in hexidecimal or a Test$ID, that is where getting the information is so important so that you can try to decipher what it is trying to tell you and is usually impossible for us at our drive-way repair level to get. The "very small leak" is truly a very small leak, under .020. There is a vapor pressure sensor in the fuel tank and when the test for the evaporative system is run a timer is running, the PCM is expecting a rise in pressure ever so slight during that tests time period. If the PCM does not detect a rise in fuel tank pressure due to a pin hole or a defective pressure sensor or anything that does not allow pressure to build in the fuel tank, a CEL is set.

If you dont have the time, the equipment or the patience to drop the tank and inspect EVERYTHING, find a good shop. I had a buddies Jeep Liberty that just wouldn't complete the drive cycle, no matter what I did. No complete drive cycle, no smog. There was some Mode 6 data but getting any information for Mode 6 on that was impossible. In CA, where I live, we have the Bureau of Automotive Repair and what are referred to as "smog Referees". It is these guys job to help with problem cars like this Jeep. I called and made an phone appointment and we talked for a few minutes he gave me a few web sites but no data was available. I asked him, If you were me, where would you take this car? He told me I took it there and they had it diagnosed and fixed and smogged in a day for under $200. I must have had 6 hrs into checking this and checking that, drive cycles attempts etc. This is one of the few cars that has beaten me, but then again, is was a Chrysler/Jeep product. I am sure that PA has the equivalent of CA smog referees.

hopefully some good info for you

https://www.emissions.org/loc/pennsylvania-emissions-testing/

 

Thank you for the explanation, that was very helpful. My code reader is about $30, and doesn't get that information. I did have the fuel pump replaced maybe 6 or 7 years ago

I did check the gas cap seal just now, and it is cracked pretty good. I do not get a whoosh sound, so I think the seal might be shot. I'm assuming its the original one. I am going to try replacing that and go from there. I don't really have the time to mess around with the code because of work, etc.

Thank you again for the help, I appreciate it!

Tom

 

I've had the same code off and on for the past year. I've replaced the gas cap, evap lines/clamps in the engine bay, and one of the vacuum switching valves. Still have the code.

From my reading another common source of this issue is the gasket between the fuel tank and fuel sending unit. I can smell gas back there in my truck, so I'm hopeful that will fix my issue, hopefully you can fix yours with just a new gas cap.

 

I saw that as well, luckily I don't smell gas anywhere outside my truck. I had my fuel pump replaced a while back so I'm guessing the gasket was done then as well. I figured the cap was the easiest thing to fix, lol.

Hope the gasket solves your the code issue for you!

 

Tjsingle26, I have the same code, 2011 tacoma stalling when going uphill. Dealer replace gas cap and engine light and traction erase but truck still stalls. then the P0456 appear. How did you figure the hose. Thanks