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Old 10-15-2013, 06:51 PM
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Default 08 Jeep Gas Cap Light

Had an 08 Jeep Grand Cherokee 3.7 in today with a check gas cap light on in the message center. No codes were stored on any modules and couldn't find any information on how to clear the light. I tried to clear the codes from the PCM any ways but it had no effect on the light. I ran the evap monitor system test. It passed and the gas cap light went out. I would have thought there would have at least been a pending evap pending code. This system uses an Evaporative Systems Integrity Module. I've looked on ShopKey but can't seem to find a theory of operation for this system. I think it's different than the NLVD system. If some one has some information on this system I would interested in reading it.

Last edited by greasybob; 10-15-2013 at 07:17 PM..
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Old 10-15-2013, 07:06 PM
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Hi Bob,
NVLD and ESIM have the same strategy. The only difference is that the ESIM valve doesn't have a solenoid in it that opens during purge. I've never seen one that didn't have a Pending P0455 stored in it when the gas cap light was on, but it sounds like you have found one. I am surprised to hear that the light didn't go out when you cleared the codes.

If you have Powerpoint, click this link for a quick demo of how NVLD and ESIM work. There is some animation that shows their operation. You'll see the ESIM valve is a pretty simple device, which is cool. On this system I have only found bad gas caps (wouldn't tighten), and bad ESIM valves (switch stuck open or closed, but became operational after a tap test).

https://dl.dropboxusercontent.com/u/...LDandESIM.pptx
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Old 10-15-2013, 07:21 PM
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Thanks, I got the file/link opened.
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Old 10-15-2013, 07:37 PM
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After I ran the Evap monitor with the verus I smoked the system to check for small leaks but I sealed the system by crimping the vent hose that comes off of the ESIM. So while I didn't find any small leaks and the flow rate was less the what .010th of inch would allow I really didn't eliminate a defective ESIM. I did see the ESIM data pid switching while the monitor was running. If I pull a regulated vacuum on the tank manually will I see the pid switch ? Is there a good test for the ESIM ?
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Old 10-16-2013, 02:34 PM
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To test the ESIM switch connect a hand held vacuum pump to the system. I use a gas cap adapter. It closes with a trace of vacuum in the system. In less than 10 pumps the ESIM switch will close. It will also close any time the Purge Valve is running more than about 25%.

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Old 10-16-2013, 06:10 PM
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While I was running the Evap Monitor I could see the ESIM pid changing from closed to open, is this normal ? I still have the vehicle here, Maybe tomorrow I'll try the pulling a vacuum on the system manually.
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Old 10-16-2013, 07:57 PM
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The only time I have seen them switch is when they are on the verge of closing. They will open/close multiple times before closing for good. If you apply vacuum manually, you will witness it.

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Old 10-17-2013, 08:35 AM
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Did some lookin around on Chryslers web site and found this:

To clear the light follow one of the 4 suggestions below: Under the PCM Misc functions perform an adaptive memory clear. Make sure the full level is between 15% and 85% then drive the vehicle for 16 to 20 miles for the vehicle to run the EVAP monitor once the monitor has passed the Gas Cap message will go off. In some cases use the StarSCAN to clear Gas Cap message by selecting ECU Reset under the PCM Misc functions or rewriting the existing mileage to the PCM under misc functions check odometer. Battery disconnect will also clear the light from the CCN but not recommented due to the loosing of all user programed functions. Pressing the Trip Odometer will not clear the Gas Cap Message on most vehicles.
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