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Mark
Mark, 22 Year Factory trained technician
Category: Jeep
Satisfied Customers: 11266
Experience:  Jeep factory training........25 years in the industry.
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2001 Jeep Grand Cherokee: OBD..vacuum lines..the engine compartment

Customer Question

OBD 1494 Code? This code is occurring all of the time now on my son's 2001 Jeep Grand Cherokee. The vacuum lines in the engine compartment look good. I have even used some starting fluid around these lines and their connections while it is running and cold and don't find any leaks. What is the usual cause for this issue? Thanks, Larry
Submitted: 5 years ago.
Category: Jeep
Expert:  Mark replied 5 years ago.

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.

Mark, 22 Year Factory trained technician
Category: Jeep
Satisfied Customers: 11266
Experience: Jeep factory training........25 years in the industry.
Mark and 7 other Jeep Specialists are ready to help you
Customer: replied 5 years ago.
From your reply, it appears to you are suggesting that the Leak Detection Pump switch may be the problem. I contacted you guys first, since I had seen a number of posts on the internet indicating that this switch is usually not the problem. I assume that this switch is the one directly in front of the large metal rectangular canister next to the firewall on the drivers side, right?
Expert:  Mark replied 5 years ago.

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.

 

graphic

 

This switch is internal to the leak detection pump, so the pump assembly needs to be replaced.

Customer: replied 5 years ago.

I found this on another post at your site...

 

NUMBER: 18-01-00

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 Van
1997 - 2000 (AN) Dakota
1997 - 2000 (BR/BE) Ram truck
1998 - 2000 (DN) Durango
1997 - 2000 (FJ) Avenger/Sebring/Talon
1997 - 2000 (JA) Cirrus/Stratus/Breeze
1997 - 2000 (JX) Sebring Convertible
1997 - 2000 (LH) Concorde/Intrepid/LHS/3OOMNision
1997 - 2000 (NS) Town & Country/CaravanNoyager
1997 - 2000 (PL) Neon
1997 - 2000 (PR) Prowler
1997 - 2000 (SR) ViperNiper GIS
1997 - 2000 (TJ) Wrangler
1999 - 2000 (WJ) Grand Cherokee
1997 - 2000 (XJ) Cherokee
1997 - 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?

Expert:  Mark replied 5 years ago.

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.

Customer: replied 5 years ago.
Thanks... I will look at the LDP first then. I appreciate your help!
Expert:  Mark replied 5 years ago.
You're welcome.
Customer: replied 5 years ago.

Mark,

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.

Thanks,

Larry

Customer: replied 5 years ago.
Do I need to pay again to receive more information about this issue even though it is not resolved?
Expert:  Mark replied 5 years ago.

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

Detection Pump.

Start the engine and read the vacuum gauge.

Does the vacuum gauge read at least 13 in/Hg?

All

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?

All

Yes ! Go To 5

No ! Repair the Leak Detection Pump Switch Sense Circuit for an

open.

Perform POWERTRAIN VERIFICATION TEST VER - 6.

5 Measure the resistance between ground and the LDP Switch Sense circuit.

Is the resistance below 100 ohms?

All

Yes ! Repair the LDP Switch Sense Circuit for a short to ground.

Perform POWERTRAIN VERIFICATION TEST VER - 6.

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?

All

Yes ! Replace the Leak Detection Pump.

Perform POWERTRAIN VERIFICATION TEST VER - 6.

No ! Go To 7

7 If there are no possible causes remaining, view repair. All

Repair

Replace and program the Powertrain Control Module in accordance

with the Service Information.

Perform POWERTRAIN VERIFICATION TEST VER - 6.

Customer: replied 5 years ago.
Hi Mark, Thanks for the additional info. Maybe this will reveal the culprit. Can you also send me the pinouts for the PCM and LDP harnesses so I will know what pins to take my measurements from? It would also be nice to have a schematic of the LDP circuit so that I can get a better picture how everything is interconnected. Thanks, Larry

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