Question about 1999 Jeep Grand Cherokee

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P1494 code How to fix or diagnose the problem

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  • Jeep Master
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Engine idle speeds, odd, hot? any real symptoms?

can be lots of things, the FSM covers it.
I think the ratio to real EVAP faILuers TO BAD CAP , IS LIKE 1000000:1 its so bad , new cars put , gas cap failure on dash !! display.
Give that fact, check cap first, and reset the ECU.
the EVAP system can be simple or hard.
Visual check the vacuum lines to all EVAP components
check all fuses.
then make sure gas cap is tight. (if cracked its no good) or a bad seal.
the reset the codes, using any scan tool. ($9 tool)
drive for a week see if it comes back, if comes back then its REAL.
if there is breach in the EVAP or bad VSV, (vacuum sol. valve)
then that takes the testing steps in the FSM.
or the EVAP system needs pressure testing, like they do
in all smog stations , at the cap.
if the leak down test fails, then you simply find that leak.
On can use any rubber tube held to the ear to hear a leak (after using a pressures source to the system.
if you have no tools, take it in. if DIY , buy them.
read the FSM. under this code, and the EVAP sections carefully.
there are 2 paths, it really is failing the EVAP or the OBD2 testing parts
are fibbing.
lots of guessing here, no tests...
http://www.jeepforum.com/forum/f11/engine-code-p1494-545078/


http://engine-codes.com/p1494_chrysler.html

Purpose
the EVAP system , keeps gas fumes from polluting the air we breath.
it seals the tank vents and burns off all fumes as you drive.
that is what it does.
and is tested, all the time by the OBD2 system.
its very reliable in finding, any failure.
Your system fails the first step, it checks to see if the system
even holds pressure, and fails. the FSM explains how this
test is conducted, the steps and checks.


Cap issues?
my current jeep , the cap ratchet was dead. and would not get fully tight.
or the vacuum breaker inside is bad. (stuck open)
or the sealing ring is bad.
or someone put wrong cap on car.
or a locking cap that is wrong.
the cap holds pressure, and never a vacuum.
the vacuum breaker prevents fuel tank collapes (photos avail)

Posted on Dec 25, 2013

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p1494
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P1494


The Dodge P1494 engine light code means Leak Detection Pump Switch or Mechanical Fault. A proper diagnosis must be done, you can't simply replace the LDP and expect that to fix the problem. It shouldn't hurt anything to keep driving it for a while until you can get it fixed.
There is a technical service bulletin that applies to your vehicle and it mentions that code specifically. I'm including it here for your information: TSB-18-01-00
SUBJECT: Misdiagnosed Leak Detection Pump Systems With DTC P1494, P0442, P0455, OR P0456.
MODELS: 1997 - 2000 (LH) Concorde/Intrepid/LHS/300M/Vision and others
DISCUSSION:
During evaporative system diagnosis, Leak Detection Pumps have mistakenly been replaced. A thorough inspection for pinched, kinked, or disconnected supply vacuum lines (as currently listed in the Powertrain Diagnostic Procedures) is a critical step in diagnosing DTC P1494 (LDP SW OR MECHANICAL FAULT). Additionally, the other evaporative leak faults (DTC P0442 - SMALL LEAK, P0455 - LARGE LEAK, and P0456 - VERY SMALL LEAK) should have the supply vacuum lines examined for pinches or kinks prior to any LDP component replacement. The supply vacuum lines should be checked from the engine compartment all the way to the fuel tank, including the LDP and purge system.

NOTE: VERIFY ALL RELATED SUPPLY VACUUM LINE ROUTINGS FOR PINCHES, KINKS, OR DISCONNECTION'S BEFORE REPLACING LDP SYSTEM COMPONENTS.

Hope helps (remember rated and comment this).

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These are all related sensors and active devices of the evap system, clear the code and replace the fuel cap.

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