P1494 What does this code mean - 1999 Jeep Grand Cherokee

didnt specify so check these links for assistance p1494 code what exactly is and where is the part located P1494 EVAP Leak Detection Pump Switch or Mechanical Fault Trouble Code P1494

P1494 Leak detection pump pressure switch or mechanical fault

P1296 No 5-Volts to MAP Sensor
P0108 MAP Sensor Voltage Too High
P0500 No Vehicle Speed Signal Circuit
P1494 Leak Detection Pump Switch or Mechanical Faul
I would try MAP sensor first.

vacume leak most common is gas cap not sealing

P1494 is a Leak Detection Pump Switch or Mechanical Fault. 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). This is a problem with evaporative emissions system and should not affect drivability. If this was helpful please leave positive rating.

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).

LEAK DETECTION PUMP SYSTEMS (P1494, P0442, P0455, P0456),

P1494 means Leak Detection Pump Switch or Mechanical Fault - This code appears when there's an issue with the EVAP System (fuel tank fumes) This can be caused by a improperly secured gas cap, faulty gas cap, crack in the vacuum line, etc.

danbalue, a code P1765 means Transmission 12V Supply Relay Control Conditions and P1494 means EVAP LDP Pressure Switch Fault Conditions.

I found info on the following codes:
P0443 - http://www.obd-codes.com/p0443
P1494 - http://www.check-engine-light.com/dodge

Good luck.

P1494 Leak detection pump pressure or mechanical fault, hope this helps