Emissions Codes P0455/P0456

[BinaryData]

P0455 Evap Leak Monitor Large Leak Detected
P0456 Evap Leak Monitor Small (0.020) Leak Detected


These two codes are currently whats causing my "check engine" light. A friend suggested I purchase a new gas cap, I've done that. Still have the check engine light, I'm going to take it to O'reilly's Auto Parts tonight, and have them clear the code. If it comes back, I think I need to check the EVAP Canister, and the hose that leads to it.

Can anyone else think of something that could cause these codes?

 

[MADDOG]

If it isn't the cap then it is usually a vacuum line in the EVAP system as you surmise. If it was an intake leak you'd get a code on the O2 sensors or an overly lean A/F ratio.

The evap lines are rubber and they get old, cracking at the point of connection much like an old radiator hose.

Good luck and let us know how things go.

 

[BinaryData]

If it isn't the cap then it is usually a vacuum line in the EVAP system as you surmise. If it was an intake leak you'd get a code on the O2 sensors or an overly lean A/F ratio.

The evap lines are rubber and they get old, cracking at the point of connection much like an old radiator hose.

Good luck and let us know how things go.

MADDOG to the rescue. Looks like it self-fixed itself? I started my truck up to go get some lunch. The code was gone, popped my ODB2 reader, and nothing. Diags came back clean, minus the low tire pressure.

I'm still going to replace that hose, 2009 is a long time for a hose, especially when the truck is from Alaska and the weather is MUCH harsher up there.

 

[MADDOG]

Sine you replaced the cap I suspect that was the specific problem.

Any code that is logged by the PCM will take 3 to 5 key cycles (Off/On) before it clears itself. You can clear them sooner by disconnecting the negative cable on your battery for about 30 minutes or clear them with a programmer, such as one of the Diablosport units.

Have fun with the hose replacement!

 

[Rampant]

MADDOG to the rescue. Looks like it self-fixed itself? I started my truck up to go get some lunch. The code was gone, popped my ODB2 reader, and nothing. Diags came back clean, minus the low tire pressure.

I'm still going to replace that hose, 2009 is a long time for a hose, especially when the truck is from Alaska and the weather is MUCH harsher up there.

Glad to hear your CEL went away. Here's some info on how the system works to help you understand why the light came on and how/why it reset itself. The conditions needed to set those particular codes are toward the bottom. If those codes do come back, this info may be helpful.

From Alldata:

EVAPORATIVE SYSTEM OVERVIEW: The Powertrain Control Module (PCM) monitors the Evaporative Emission System operation. The two main areas being monitored are the integrity of the system against leaks and the ability of the system to get fuel vapor from the canister to the Intake Manifold. The basic strategy used is that in a sealed system , pressure will naturally increase or decrease in relation to temperature. As temperature increases, so does pressure inside the system. And conversely, as temperature decreases, vacuum is created if no leaks are present. The Evaporative System Integrity Monitor (ESIM) Switch has multiple functions. There are two weighted seals that keep the system normally closed from the atmosphere. The two weighted seals are used to regulate the system pressure between 250 Pa (+1" H2O) and -500 Pa (-2" H2O). There is also a vacuum actuated switch that closes when the vacuum reaches a calibrated value. During cooling, the internal weights seal the evaporative system from the atmosphere and allow the switch to close. If the switch closes it indicates that the system is not leaking. Only the ESIM Switch is used for leak check diagnostics. The Fuel Tank Pressure (FTP) Sensor is not used for diagnosing the system for small leak or large leak testing.

SMALL LEAK MONITOR: This is an accumulative monitor and the data from each valid event is recorded and added to the previously recorded events. The PCM timer records the engine on/drive cycle and engine off time for each small leak monitor event. For an event to be valid the PCM must see;

1. An engine on/drive cycle for a minimum of 2 - 5 minutes. NOTE:The Engine on timer is clipped to a maximum of 26 minutes on any given trip.
2. And, when the engine is shut down, an engine off timer starts. There is a 12 minute delay time in which the PCM will ignore ESIM Switch input. The engine off timer period will continue to count until one of the three conditions exist:

- The engine is started without a switch closure during the event.
NOTE:At the next key on cycle a determination is made as to whether the event was valid and the information is kept.

- An ESIM Switch closed input is received after the 12 minute delay during the event.
NOTE:If the switch closed input is received, the PCM records that the switch has closed and stores the engine shut down time.

- After a maximum time of 17.5 hours without an ESIM Switch closure during the event.

This monitor will increment the accumulation fail timers until both have reached a calibrated threshold (Engine on - 100 minutes and Engine off - 70 hours). When the monitor records a valid switch closure (small leak passing event) the fail timers are reset.

LEAK SIZE DETERMINATION: If the PCM did not see an ESIM Switch closed signal during the previous ignition off cycle, the event was valid, and there is a cold start, an intrusive leak test is run to determine if a large leak is present. Immediately after start-up, while the engine is cold the Purge Solenoid is opened to create vacuum in the evaporative system to a calibrated vacuum point that is beyond the ESIM Switch closing threshold. The pass/fail time will vary based on the total fuel volume at the time of the test.

- If the switch does not close at all during purging, because of a switch that is stuck open or vacuum cannot be created below 1.0" H2O within a calibrated time, it is determined to be a general evaporative system failure (P0440).

- If vacuum is created and the switch has closed, the PCM stops purging and monitors the switch closure time. If the switch opens before a calibrated time, a large leak is present. Two consecutive failure events will mature a fault (P0455).

- If vacuum is created and the switch has closed, the PCM stops purging and monitors the switch closure time. If the switch stays closed longer than a calibrated period of time, it is determined that a large leak is not present and the Small Leak Monitor will continue to run until the accumulative monitor reaches its threshold. If no ESIM Switch closures were recorded during the entire accumulated timer, it is determined that a small leak is present (P0456).

When Monitored and Set Conditions

When Monitored: This diagnostic runs continuously when the following conditions are met:

- On a cold start condition when the Evap System Small Leak test has failed during the last valid ignition off event.

- Ambient temperature between 4°C and 35°C (39°F and 95°F).

- Fuel level is between 12% and 88%.

- Elevation is below 8000 feet.

Set Conditions:

- The Powertrain Control Module (PCM) initiates an intrusive test to determine the leak size. During the test the ESIM switch opened before a calibrated period of time, indicating a large leak is present.

 

[BinaryData]

Interesting.. I'll have to read this in depth when I have some free time off from work. Some really good information to know.

 

[scott lass 18]

P0455 Evap Leak Monitor Large Leak Detected
P0456 Evap Leak Monitor Small (0.020) Leak Detected


These two codes are currently whats causing my "check engine" light. A friend suggested I purchase a new gas cap, I've done that. Still have the check engine light, I'm going to take it to O'reilly's Auto Parts tonight, and have them clear the code. If it comes back, I think I need to check the EVAP Canister, and the hose that leads to it.

Can anyone else think of something that could cause these codes?

I had to replace to a better lock cap then three years later did one again years now seems ok yes you have to clear all codes when u fix things ok good luck !

 

[BinaryData]

Thanks man. I got it fixed, new gas cap did the job. Bummer it was $20 for the darn thing.