I have a 2000 cherokee sport with the engine light on
Checked the codes and came up with P0441 which said Evaporative emission purge flow monitor malfunction and P1494 Leak detection pump switch or mechanical malfunction. From doing some research I understand the somewhere in the evap system there is a leak. A lot of suggestions say to check the vacuum lines to the manifold and mine seem solid. Anyone have this issue or have suggestions? Much appreaciated

 

Sounds like your Leak Detechion Pump Switch has taken a dump. Try replacing it.

Check all the vacuum tubes from the LDP/engine bay all the way back to the Charcoal Canister, and from the canister to the roll over valve on top of the gas tank. Look for the roll over tube (steel) to be rusted out. Check/replace the gas cap with an OEM cap.

 

That same error code P1494 just popped up on my 2001 Jeep Cherokee Sport with the 6 cylinder engine.

As soon as I start the engine the check engine light comes on. I can zero the code and start back up with no light, but when the car sits over night, the light comes on with the next start.

For about two or three years when it got cold (less that 40 degrees) after about 10 minutes the check engine light comes on with a P0456 (Evap leak monitor small leak detected). I could reset it and as long as it was warm (90% of the time here in Louisiana) the light never came on again.

I did a complete check of all the tubes, plastic pipes, fittings, hoses and can't find a thing. But since it was an infrequent issue, I just kind of lived with it.

But now with the P1494 code it points to a specific part, which is available from Mopar for $147.00, ouch! They said they did not show a "switch" which makes me think it must be an integral part of the pump.

Before I cough up the bucks I'm going to take the LDP off, clean it up, check for obvious problems, clean up the electrical contacts and try to do some analysis of whether voltage is present when I start the engine to make sure it's not electrical upstream of the pump.

Might even go the junkyard route and spend a few bucks for a used one just to see what happens.

Anybody out there got any other ideas where I might want to look?

 

Thanks for the advice, sorry if this is a stupid question but Im not a certified mechanic, do you know where that leak detection pump is located? and how hard to replace?

 

It's located on the passenger side, just forward of the fire wall, and mounted to the top of the fender well with three screws. On top of it is a small filter cannister that is mounted to the LDP bracket with a single screw. There is a large hose on the bottom and a smaller one on the rear of the top. A single electrical plug is connected on the front, with a red locking tab. The screws are all 10 mm, and the three that fasten the LDP (it's plastic) to the metal bracket are phillips head.

I'll take some pix later today and scan the page in my FSM, then post them here.

I took mine off yesterday, cleaned it up, used compressed air to blow out the ports (not much dirt inside) and cleaned the little air filter on the top, again not much dirt. (car has 100,000 miles on it) I put everything back on and, knock on wood, the P code cleared. The hoses were all in good shape so I didn't have to replace any of them.

I'm not a certified mechanic either, just been working on cars for nearly 60 years.

 

Here's an annotated picture of the Leak Detection Pump.



Removal is pretty straight forward.
1. Start with the big hose on the bottom that goes to a metal tube that runs behind the engine. Pull the rubber hose off the tube and remove the LDP with the rubber hose connected. (Really hard to get to that hose which is on the bottom of the LDP with it in the car)

2. Disconnect the smaller rubber hose from the back of the LDP.

3. Unscrew the air filter on the top and pull it out of it's rubber tube.

4. Pull up on the red lock tab on the electrical connector and pull it off the LDP.

5. Take out the three screws attaching the bracket to the fender well and work the LDP out. The bracket can then be removed from the LDP.

I took the end off the filter cannister and cleaned the cannister, then the filter with compressed air.

I also blew the various ports of the LDP out. I used Orange degreaser to clean it up.
I don't know if a new LDP comes with the filter or not. If you are getting a new LDP don't get rid of any hoses off the old one, just in case you need them.

Good luck.

UPDATE: wife just drove the car and said the check engine light came back on. Damn! I drove it this morning with no problem, so I may have to replace the LDP after all.

 

Have you replaced your gas cap?

 

Yes, but not before I had taken out the LDP cleaned, checked operation of the internal relay, voltage in the wiring harness and put it back in. I cleared the 1494 code and started the engine, no problem, no code. So then I put the new gas cap on.

Next day I drove the car (it was cold which used to be a problem in generating a 0456 code) and again no problems with the 1494 code.

However, about 4 hours later my wife drove the car (it's her daily driver) and she said as soon as she started it the MIL light came on. I did a scan and sure enough the 1494 was back.

So I'm going to check and clean the connection where the LDP gets it's signal from the PCM, as well as clean the plug on the LDP itself. I didn't have any electrical contact cleaner when I first removed the LDP.

If that doesn't fix the problem, I'm probably to the point to where I'll have to spring for a new LDP as I can't find one in the local salvage yard.

There is a "service port" on the evap system, but I can't find any procedures in the FSM regarding it's use. I'm assuming it's for either pressurizing or applying a vacuum to the system, but beyond that, nothing. I'm not about to do either one unless I can find out how much pressure/vacuum to use.

This whole exercise is kind of a pain in the *** as there is no discernible change in the way the engine runs, or the car drives, just that damned MIL light coming on!

The only other thing that might be the problem is the EVAP Cannister itself, although there are no specific error codes listed for that, so other than changing it, not much else I can do.

The last thing is the PCM. I know there is input from and output to the LDP from the PCM. But I can't find any specifics, i.e. when and voltages. I do know one of the wires to the LDP is 12v when the engine is running, but that's about the extent of it. Again the FSM mentions it, but doesn't give any specific test procedures or parameter es.

My wife did come up with one sure fire fix, "Put a piece of tape over the check engine light"!

UPDATE: Just went out and started it up. No MIL light. Let it run a while, shut it off, started it up again, and the light came on. (Yesterday I did the same thing, and the light never came on even after I had driven 5 miles, shut it off, then started up and drove back the same 5 miles.)

Didn't hook the scanner up, but I'd bet it's the LDP. I know it goes through a test and what it does, but not what triggers the test, i.e when engine is started, or just ignition turned on. Oh well....life goes on.

 

That fix works for every code in the book!

If all connections and lines are good, I think I'd swap out the pump itself.