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Check Gas Cap Indicator Keeps Appearing

57K views 14 replies 7 participants last post by  meegwell 
#1 ·
I've searched and read a lot of messages concerning this issue and have not found any that go as far as my situation w/ a resolution.

08 5.7 limited w/ 13k miles.


Check Gas Cap message came on, followed by Check Engine Light (I understand why the check engine light comes on following the Check Gas Cap, and I understand the whole evap pressure system as the root of the indicator).

I checked the gas cap (duh). Light and message still still on (for days of driving).

First Service visit: They did a "pressure test" and it passed. They reset the lights and "tightened up" the gas cap. I knew I'd be back since I was sure I tightened the gas cap but crossed my fingers and left.

Few days later: Check Gas Cap message came on, followed by Check Engine Light

Second Service visit: They did a "smoke test" to look for leaks. No leaks found. They replaced the gas cap with a new one, citing possible bad seal or sensor. They also replaced the "solinoid" or something similar sounding. Reset lights. I crossed my fingers and left.

Few days later: Check Gas Cap message came on, followed by Check Engine Light
Third visit is scheduled for Tuesday, they asked I leave it over night so they can test it cold.

Anyone been here before or have any ideas/knowledge?

Summary:

  • Smoke test and pressure test passed.
  • Gas cap was replaced with a new one.
  • "solinoid" or something like that was replaced.
  • Check Gas Cap (evap leak indicator) still comes on.
  • Check engine light follows (as expected due to the first problem)
This sux because the remote start will not work w/ a check engine light on...and I like the remote start for loading young kids in the jeep on cold mornings.


Meegwell
 
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#2 ·
Thank the EPA, they made the standard for the EVAP system so ridiculously high that people are going nuts and dropping tons of cash trying to correct a non-existent problem.

OBDII is a federal standard that requires vehicles to use its engine control computer to self-test the vehicle for meeting all federal emissions standards.

You are failing the evap test, because the Chrysler Test System is reacting like it has a leak. NOTE, I said the system is reacting like it has a leak, NOT, that it actually has a leak.

Of course the manufacturer is going to try to develop the cheapest most reliable system to perform this test. Its NOT done in a laboratory, but they need a laboratory like test performed on a moving vehicle. So they come up with this tortured system of a cheap vacuum pump, that actually pumps up over pressure in the fuel system, using engine vacuum controlled through a electric solenoid valve, and a little read switch and the computer monitors how often and how fast the diaphragms in the vacuum pump go back and forth at full deflection, to tell if there is a leak or NOT.

The computer has no idea what the pressure is in the fuel system and evap system, NOR whether there is a leak or NOT. All it knows is that diaphragms in the vacuum pump go up and down fast enough and stops moving within a certain time. If it doesn't, then there must be a leak.

Thats why they replaced the solenoid valve, it controls the vacuum pump.

I've replaced half the Evap system on my Neon R/T before the Evap CEL stopped coming back. It still comes back every once in a while, I clear it and it seems to go away for a year or two.

Its been a real problem for all the manufacturers, a vehicle gets an evap DTC and they can't figure out what is causing it, and even its a leak or NOT, or if its something in the detect system causing it to erroneously detecting a leak.
 
#3 ·
I recommend pouring a bit of a gas on the ground, preferably near a lake or a stream. It won't fix your problem but at least you can get even with the EPA.

Anyone know if the evap system is listed as a "major control component"? If so it has a 8 year, 80,000 mile warranty. Keep taking it to the dealer, I don't know how else you're going to get something so dumb and specialized fixed.
 
#4 · (Edited)
Do you turn off your vehicle when fueling it? When you tighten your gas cap does it click and if so his many clicks? What has the temperature been?

I really don't think the EPA is out to get you like the other conspiracy theorist's. EPA just set the standard, is it their fault that a company built a inferior product that has issues meeting the standard?

The funny part is Ford apperently meets the standard and some of their vehicles don't even have gas caps. So it can't be that hard!
 
#9 · (Edited)
The system works by vacuum, At startup the fuel tank has vacuum pulled, to ck for leaks. If the system can't be pulled down, it triggers a fault code. It could be a number of compnents. The vapor canister, one of many hoes in the sytem, the gas cap, fill tube, etc. They need to inspect some of the lines, for a possible leak, the canister for proper operation, & the purge solenoid, to name a couple of possible things.
 
#14 ·
The system works by cacuum, At startup the fuel tank has vacuum pulled, to ck for leaks. If the system can't be pulled down, it triggers a fault code. It could be a number of compnents. The vapor canister, one of many hoes in the sytem, the gas cap, fill tube, etc. They need to inspect some of the lines, for a possible leak, the canister for proper operation, & the purge solenoid, to name a couple of possible things.
Motorcity, my apologies, I just checked the FSM and it seems Jeep went back to the vacuum system. For years prior, Chrysler had gone with a over pressure pump system, like the Japanese and Germans; that was what I was describing. BUT, like I said before, its the same concept just different implementations.

OK, now let me confuse the issue even more by telling you what the fellow that made my auxillary gas tank told me. I do consider Jake to be an expert. He told me that the Commander pressurizes the tank and compares the pressure to a known value for the gas level guage reading from the fuel level sensor. He told me that I might get the error code for a loose gas tank because of the additional space from the second tank. I have had an error twice. Both times they cleared right away with a disconnect of the battery ground cable. Knowing this probably does not help but it does show that the system is very complicated.
Well, the PCM never reads an actual pressure from what I understand, it "infers" a pressure, but how the pressure pump reacts or in the case of a vacuum system, how the vacuum valves react. i.e. how long it takes for pressure/vacuum to bleed down and cause a change in poppet valves or the pump.

The way he said it, isn't wrong, it just wasn't the whole story. As far as comparing fuel level, I've never read that, BUT, it doesn't initiate the test unless you are at a certain range of fuel level. So, what he says makes sense, and is probably what is behind the reason why the test is NOT initiated
unless you are at a certain range of fuel in the tank. i.e. a big difference in empty volume in the tank would change the length of time for bleed down time and the reaction of poppet valves and/or pumps, that the computer sees and is timing.

This is what I found in the 2007 FSM, it references another type of system, so there may have changed the evap systems during different M/Y of Commanders.

OPERATION

SYSTEM

1 - Intake Manifold

2 - Throttle Body

3 - Purge Solenoid

4 - Filter

5 - ESIM

6 - Vapor Canister

7 - Control Valve

8 - Fuel Tank

9 - Gas Cap

The ESIM (Evaporative System Integrity Monitor) is very similar to the NVLD. However, the design of the ESIM has been simplified and unlike the NVLD the ESIM does not require a solenoid. The ESIM mounts directly to the canister, eliminating the need for a mounting bracket. It is critical that the ESIM is mounted vertically. On vehicles where the canister is mounted on an angle, the ESIM requires an adaptor to maintain a vertical position. When the ESIM is installed vertically, the electrical connector is in the 3 o'clock position.

EXPLODED VIEW

1 - ESIM Housing

2 - Diaphragm

3 - Switch

4 - Cover

5 - Small Check Valve

6 - Large Check Valve

The ESIM assembly consists of a housing, a small weight and a large weight that serve as check valves, a diaphragm, a switch and a cover. There is one large weight and one small weight check valve in the ESIM assembly. A seal is attached at the end of each weighted check valve. The large weight check valve seals for pressure. The small weight check valve seals for vacuum. The weighted check valves are contained within the ESIM housing.

CUT AWAY OF MODULE

1 - Large Check Valve

2 - Fresh Air Inlet

3 - Diagram

4 - Small Check Valve

5 - Vapor Canister

The ESIM (Evaporative System Integrity Monitor), while physically different than the NVLD system, performs the same basic function as the NVLD does – controlling evaporative emissions. The ESIM has been simplified because the solenoid used on the NVLD is not used on the ESIM.

The ESIM consists of housing, two check valves (sometimes referred to as weights), a diaphragm, a switch and a cover. The larger check valve seals for pressure and the smaller one seals for vacuum.

During refueling, pressure is built up in the evaporative system. When pressure reaches approximately .5 inches of water, the large check valve unseats and pressure vents to the fresh air filter.

Conversely, when the system cools and the resulting vacuum lifts the small check valve from its seat and allows fresh air to enter the system and relieve the vacuum condition. When a calibrated amount of vacuum is achieved in the evaporative system, the diaphragm is pulled inward, pushing on the spring and closing the contacts.

The ESIM conducts test on the evaporative system as follows: An engine off, non-intrusive test for small leaks and an engine running, intrusive test for medium/large leaks.

The ESIM weights seal the evap. system during engine off conditions. If the evap. system is sealed, it will be pulled into a vacuum, either due to the cool down from operating temperature or diurnal ambient temperature cycling. When the vacuum in the system exceeds about 1” H20, the vacuum switch closes. The switch closure sends a signal to the GPEC1. In order to pass the non-intrusive small leak test, the ESIM switch must close within a calculated amount of time and within a specified amount of key-off events.

If the ESIM switch does not close as specified, the test is considered inconclusive and the intrusive engine running test will be run during the next key-on cycle. This intrusive test will run on the next cold engine running condition.

Conditions for running the intrusive test are:

After the vehicle is started, the engine coolant temperature must be within 50°F (10°C) of ambient to indicate a cold start.
The fuel level must be between 12% and 88%.
The engine must be in closed loop.
Manifold vacuum must be greater than a minimum specified value.
Ambient temperature must be between 39°F and 98°F (4°C and 37°C) and the elevation level must be below 8500 feet.
The test is accomplished by the GPEC1 activating the purge solenoid to create a vacuum in the evaporative system. The GPEC1 then measures the amount of time it takes for the vacuum to dissipate. This is known as the vacuum decay method. If the switch opens quickly a large leak is recorded. If the switch opens after a predetermined amount of time, then the small leak matures. If the switch does not close, then a general evaporative failure is recorded. The purge monitor tests the integrity of the hose attached between the purge valve and throttle body/intake. The purge monitor is a two stage test and it runs only after the evaporative system passes the small leak test.

Even when all of the thresholds are met, a small leak won’t be recorded until after the medium/large leak monitor has been run. This is accomplished by the GPEC1 activating the purge solenoid to create a vacuum in the evaporative system. The GPEC1 then measures the amount of time it takes for the vacuum to dissipate. This is known as the vacuum decay method. If the switch opens quickly a large leak is recorded. If the switch opens after a predetermined amount of time, then the small leak matures. If the medium/large leak test runs and the ESIM switch doesn’t close, a general evaporative test is run. The purge solenoid is activated for approximately 10 seconds, increasing the amount of vacuum in the system. If the ESIM switch closes after the extended purge activation, a large leak fault is generated. If the switch doesn’t close, a general evaporative system fault is generated.

The purge monitor tests the integrity of the hose attached between the purge valve and throttle body/intake. The purge monitor is a two stage test and it runs only after the evaporative system passes the small leak test.

Stage one of the purge monitor is non-intrusive. GPEC1 monitors the purge vapor ratio. If the ratio is above a calibrated specification, the monitor passes. Stage two is an intrusive test and it runs only if stage one fails. During the stage two test, the GPEC commands the purge solenoid to flow at a specified rate to force the purge vapor ratio to update. The vapor ratio is compared to a calibrated specification and if it is less than specified, a one-trip failure is recorded.

The ESIM switch stuck closed monitor checks to see if the switch is stuck closed. This is a power down test that runs at key-off; when the GPEC1 sees 0 rpm’s, the purge solenoid is energized for a maximum of 30 seconds, venting any vacuum trapped in the evaporative system. If the switch opens or was open before the test began, the monitor passes. If the switch doesn’t open, the monitor fails. This is a two-trip MIL. The star scan tool can be used to force the ESIM switch stick closed monitor to run.

The GPEC1 also uses the ESIM to detect a loose or missing gas cap. The GPEC1 controller looks for a change in the fuel level (25% minimum) and then gas cap is loose or missing. If a medium/large leak is detected, a loose gas cap light illuminates and a pending one-trip fault code is set. On the GPEC1, this is a three-trip fault before the code matures
 
#11 ·
Actually the Chrysler system nows pumps up the system with air pressure, using a vacuum "operated" pump. Basically engine vacuum runs the pump that pumps air into the fuel system to check for leaks.

The system has been pressure and smoked tested by the dealer, if there was an actual leak, the pressure test would have shown it, the smoke check would have shown the exact location of the leak.

Although I agree, at this point, probably a visual inspection of every component and replacing any suspect connections should be done, a lot of rubber boots that connect part can develop dry rot and crack, possibly just enough to cause an intermittent leak.

Ideally, if the system passes a pressure test, there is no leak, so the fault should be in the equipment that is looking for a leak, i.e. the computer is erroneously seeing a leak that is NOT there. That is why they replaced the solenoid valve, it controls the pump. And the computer has no pressure sensors, it purely judges if there is a leak off how the pump reacts when it is energized, so they therefore suspect the pump's main control is faulty, the solenoid valve.

BUT, the EPA set the standard at a leak no greater than a 500 micron hole, so you very much in the territory of a leak that is impossible to find and can be intermittent, showing no leak at all sometimes and leaking at other times.

You have to think to yourself, how much raw fuel fumes are going to escape a 500 micron leak? Yet, that is what the EPA sets as the standard, and people end up going to the mechanic dozens of times trying to find the leak and can never find it, or what is wrong with the system.

BTW, the PCM has certain parameters for when it performs the test, usually the motor needs to be cold soaked, i.e. sit overnight and totally cold, the ambient air temp down near 40°F, and it performs the test at first start up under those conditions, that is why the dealer wanted you to leave the vehicle overnight.

I've often suspected the pump itself being bad, after all, if it had the slightest leak, it would NOT pump as quickly and the computer would see that as a leak in the system, since it never looks for a leak in the pump. The pump is NOT part of the pressure check, its NOT part of the evap emission system, the solenoid valve opens for it to pump up pressure to check the system. I've contemplated replacing it, but at $110, I want to be sure. Right now, my Neon R/T only intermittently sets a CEL and DTC for the evap system, I clear it and it usually does NOT come back for a year or more, so I'm keeping my fingers crossed.

What fixed the evap system on my neon, at least to an acceptable level of only intermittently and rarely setting an evap DTC, going back several times and replacing all the rubber pieces in the system. When I finally got to the last couple on top of the gas tank and filler neck, did I get some better response. Those last couple did show some signs of dry rot.

BTW, if you DIY, make sure to use fuel hose, the fuel fumes are corrosive and will eat away at most rubbers.
 
#13 ·
OK, now let me confuse the issue even more by telling you what the fellow that made my auxillary gas tank told me. I do consider Jake to be an expert. He told me that the Commander pressurizes the tank and compares the pressure to a known value for the gas level guage reading from the fuel level sensor. He told me that I might get the error code for a loose gas tank because of the additional space from the second tank. I have had an error twice. Both times they cleared right away with a disconnect of the battery ground cable. Knowing this probably does not help but it does show that the system is very complicated.
 
#15 ·
original poster here. Wow, didnt mean to stir up so much dust!

For the poster that asked if I fuel with engine running or if the gas cap clicks, read the original post.

As far as the EPA and the system, I believe they both stink. I knew the EPA was of giant waste of my tax dollars long before I had this gas cap problem!


My solution will be to keep bringing it back to the dealer.

THanks all,

Meegwell
 
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