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/
Set Condition: The state of the switch does not change when the solenoid is energized.
The LDP is located in the left/front corner of engine compartment below air cleaner housing. It is mounted to left/front inner fender sheet metal. The LDP and LDP filter are replaced (serviced) as one unit.
This switch is internal to the leak detection pump, so the pump assembly needs to be replaced.
I found this on another post at your site...
GROUP: Vehicle Performance
DATE: Feb. 4, 2000
SUBJECT:Misdiagnosed Leak Detection Pump Systems With DTC P1494, P0442, P0455, OR P0456
MODELS:1997 - 2000 (AB) Ram Van1997 - 2000 (AN) Dakota1997 - 2000 (BR/BE) Ram truck1998 - 2000 (DN) Durango1997 - 2000 (FJ) Avenger/Sebring/Talon1997 - 2000 (JA) Cirrus/Stratus/Breeze1997 - 2000 (JX) Sebring Convertible1997 - 2000 (LH) Concorde/Intrepid/LHS/3OOMNision1997 - 2000 (NS) Town & Country/CaravanNoyager1997 - 2000 (PL) Neon1997 - 2000 (PR) Prowler1997 - 2000 (SR) ViperNiper GIS1997 - 2000 (TJ) Wrangler1999 - 2000 (WJ) Grand Cherokee1997 - 2000 (XJ) Cherokee1997 - 1998 (ZJ) GrandCherokee
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.
From your experience with Jeep's, how often is this problem caused by the LDP? Are you saying that this is usually the problem?
Yes, I'm aware of that bulletin......but you will notice an 01 Grand Cherokee is not listed.
From my experience I would say better than 80% are fixed by replacing the pump.
I have now replaced the LDP as you suggested which I purchased new from the dealer. Unfortunately, we are still getting 1494 OBD codes. Please advise as to what you recommend doing next.
Alright well here is the diagnosis procedure for this code.......it gets pretty involved and you may or may not benefit from this as the correct tooling is important to a correct diagnosis.
Turn the ignition off.
Disconnect the vacuum supply hose at the Leak Detection Pump.
Connect a vacuum gauge to the disconnected vacuum supply hose at the Leak
Start the engine and read the vacuum gauge.
Does the vacuum gauge read at least 13 in/Hg?
Yes ! Go To 4
No ! Repair leak or obstruction in vacuum hose as necessary.
Perform POWERTRAIN VERIFICATION TEST VER - 6.
4 Turn the ignition off.
Disconnect the Leak Detection Pump harness connector.
Disconnect the PCM harness connector(s).
Measure the resistance of the LDP Switch Sense Circuit from the PCM harness
connector to LDP harness connector.
Is the resistance below 5.0 ohms?
Yes ! Go To 5
No ! Repair the Leak Detection Pump Switch Sense Circuit for an
5 Measure the resistance between ground and the LDP Switch Sense circuit.
Is the resistance below 100 ohms?
Yes ! Repair the LDP Switch Sense Circuit for a short to ground.
No ! Go To 6
6 Connect the PCM harness connectors.
Ignition on, engine not running.
With the DRBIIIt in Inputs/Outputs, read the Leak Detect Pump Sw state.
While observing the Leak Detect Pump Sw state, connect a jumper wire between a
good 12 volt source (B+) and the LDP Switch Sense circuit.
Did the Leak Detect Pump Sw state change when the jumper was connected?
Yes ! Replace the Leak Detection Pump.
No ! Go To 7
7 If there are no possible causes remaining, view repair. All
Replace and program the Powertrain Control Module in accordance
with the Service Information.