1999 jeep grand cherokee, error code 1494

P1494 Leak detection pump pressure switch or mechanical fault

P1491 Rad Fan Control Relay Circuit An open or shorted condition detected in the radiator fan control relay control circuit. This includes PWM solid state relays.P1495 Leak Detection Pump Solenoid Circuit An open or shorted condition detected in the Leak Detection Pump (LDP) solenoid circuit.P0753 (M) Trans 3-4 Shift Sol/Trans Relay Circuits An open or shorted condition detected in the overdrive solenoid control circuit or Trans Relay Circuit in JTEC RE transmissions. Was MIL code 45. P0753 (M) Trans 3-4 Shift Sol/Trans Relay Circuits An open or shorted condition detected in the transmission 2-4 shift solenoid circuit (4-speed auto. trans. only).P0136 (M) 1/2 O2 Sensor Heater Circuit Malfunction Oxygen sensor heater element malfunction.

Aside from getting into an accident and having your wiring harness severely damaged, the other likely suspect is your PCM. These codes are not related to each other and indicate a much larger problem.

this is what I found for that code:Leak detection pump pressure switch or mechanical fault. I assume it's the fuel pump.

This is a code for the leak detection pump and you will not notice a difference in the way the vehicle runs as this is just a vapor leak for the fuel system (emissions component) so has no effect on how it runs. Normally when getting this code the leak detection pump needs replaced.

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Jose.

p-1494 is a Leak detection pump switch or mechanical fault within the EVAP system. The possible causes are; An intermittant bad connect in the wiring harness or at the EVAP pump. The EVAP pump is faulty, broken or disconnected vacuum hose within the EVAP system. This code can be very challenging, even to an expert.

P-1494 LEAK DETECT PUMP SWITCH OR MECHANICAL FAULT

The most common cause for this code to set is a failure of the switch inside the leak detection pump. When this occurs, the pump needs to be replaced. The LDP is located in the right-rear side of engine compartment.

0301 is cyclinder 1 miss fire,check coil pack and spark plug,plug first,1494 is the fan relay,It's in the right front of the engine compartment. Kind of behind and below the RF headlamp and in front of and below the fuse box.
Easy to replace, just unplug it and plug the new one in.
The relay is the most common cause for that code with a no fan operation condition, we see it all the time.

P1494 - LEAK DETECTION PUMP SWITCH OR MECHANICAL FAULT

When Monitored: Immediately after a cold start, with battery/ambient temperature between 40 deg. F and 90 deg. F and coolant temperature within 10 deg. F of battery/ambient.

Set Condition: The state of the switch does not change when the solenoid is energized.

This code sets when the LDP Switch does not close when the vacuum is let into the LDP. An evap leak will not set this code. First check the vacuum to the LDP. IF it is ok, you will need a wiring diagram to check the battery voltage, and the control wire, and the switch state wire to the LDP. If the wiring to the LDP is good, then the switch in the LDP is bad, and you replace the LDP. This is the case almost 100% of the time.

Good luck.

smoke test for leaks.

it may not be the leak detection pump..what codes did it show...a cracked hose going to the pump..the purge solenoid or the fuel pump can cause a leak