Hey everyone,

I have a 98 Cherokee classic 4.0l auto that I have been trying to get the evap monitor to clear. No check engine lights and I have driven it over 1000 miles since resetting the codes. For some reason the evap monitor is still incomplete and I can't figure out why. What causes should I be looking into?

 

The EVAP system likes to see a lot of idling time and a lot of deacceleration before it will set. My suggestion, let it idle for 15 min, drive it around and downshift everywhere instead of using the brakes. Do a 5 mile loop, shut it off, restart it and do the same. It may take a couple key cycles but it will eventually clear or set a code.

 

How full is your gas tank?
I find with my '00 the lower the amount of gas in there the longer it takes.
3/4 of a tank or better Evap is good to go in 26 miles.
Now that is a couple cycles mind you.

 

I've gone through several tanks of gas. From full to empty. Tried doing the drive cycles a few times but it didn't work.

 

The computer might still be trying to decide if there is a problem.
Are there any pending codes?

 

No pending codes

 

My guess is that it is going to throw a CEL sooner or later.

Have you replaced any parts?

I think if this were happening to me I would go over the whole system and check the hoses.
Apparently Post #5 here is everything that constitutes the Evap System.

https://www.cherokeeforum.com/f2/diagram-14618/

Would check all my grounds and battery terminals.
Also look at the computer itself making sure that connectors are on good and nothing jumps out at me about the wiring.

If nothing jumped out at me I would replace the gas cap just cause it is not to expensive and easy.

Then I would reset the computer with this method.

https://www.cherokeeforum.com/f2/jee...ocedure-46047/

Figure lets start over and see what happens.

I came across this in my travels. I always assumed it was a procedure to get monitors to come up more quickly.

http://www.obd2.com/support/reprog/d..._procedure.pdf

So maybe just try the Evap procedure before you do anything and see what happens.

Or maybe just throw on a new gas cap without doing anything else and see what happens.

 

If your not having any problems because of it I wouldn't worry about it. I got rid of my evap system long ago.

 

Are you coming up on some sort of smog test? If not, don't worry about it.

If so, or it just bugs you (it would bug me), the look the at the links Ralph77 posted. One is the drive cycle you need to perform to get the monitors to pass. I would clear the codes, then follow the drive cycle.

Good Luck

 

Catalyst Monitor Drive Trace
Pre-Conditioning Requirements:
- MIL must be off.
- No DTCs present.
- Fuel level is between 15% and 85% full.
- ECT above 70º F.
- Engine must have run at least 90 seconds
- Engine between 1,350 & 1,900 rpm.

Does the above bolded statement mean to idle it that high or is it supposed to Rev that high on start up?

 

Thank to all on this Forum.
2001 Grand Cherokee 4.0L, 193k, orig owner with 3rd Jasper motor installed, all under warranty(a whole other story).
Tried to clear Evap Sys Monitor Not Ready for >1 month.
I have pending p0141/p0161 codes which intermittently triggered CEL but would shut off on its own- FYI post cat sensors changed x2 with NTK’s. CEL goes off every time I use QUICKSILVER/QUICKKLEEN Engine/Fuel Sys Cleaner- I know I have fouled cats(a whole other story, haha)
After 4 drive cycles over a week, Evap Sys now READY(5/16/26)
what I did-
​​​​​​— 1/4-1/2 fuel, today 1/4 tank
-5 min idle on cold engine
- Then drive to highway about 1/2 mi from home and drove at 55-60mph for 5-6 mi
- off highway idle for 5 min
- Then another 5-6 mi at 55-60
- engine off for 10 min
OBD check and Viola’ Evap sys ready