#127232, "P1494 - Can't figure it out. Need the light off." Aug-14-09 08:42 AM by WIDECLIPSE
P1494 LDP switch/ mechanical fault.
This is straight from the service manual.
Description
Immediately after cold engine start-up (if all Leak Detection Test enabling conditions listed), the PCM detects the LDP switch status. Under normal operation, the LDP switch is initially on, and the PCM turns the LDP solenoid on and the LDP diaphragm is pulled up by engine vacuum, causing the LDP switch to turn off.
+If the PCM detects that the LDP switch was initially off, it could be due to a failed LDP switch or an open circuit. If the system was sufficiently purged, the PCM then sets DTC 184. However, insufficient EVAP system purge on the previous drive cycle can allow residual pressure to remain in the system and hold the LDP diaphragm up and hold the switch off. DTC 184 will not set if the system was not sufficiently purged.
+If the PCM detects that the LDP switch was initially on and does not turn off within 2.1 seconds of the solenoid turning on, the PCM sets a "fault". If this occurs in two consecutive cold start-ups when all Leak Detection Test enabling conditions are met, DTC 184 will set.
DTC 184 can be set under any of the following conditions: Insufficient vacuum supply to the LDP LDP internal mechanical malfunction LDP switch malfunction LDP switch circuit or PCM malfunction
I have a late 98 model with the LDP being in the back by the tank. I have replaced the LDP with a brand new one. MY problem is probably the second point listed because the CEL does not come on immediately. It only comes on after the second consecutive cold start-up. This makes me think that there is a vacuum leak somewhere and it's causing the diaphragm in the LDP to not be pulled up therefore not turning the switch off. The big hoses connected to the LDP all looked fine. Connector going to the LDP is fine.
Is there any other place I can look for vacuum leaks associated with this? Could there possibly be something else going on that I'm missing?
#127242, "RE: P1494 - Can't figure it out. Need the light off." In response to Reply # 0
Not 100% sure what the LDP is, but it sounds like you may have a similar problem to one that I had. The fuel vent valve, or roll over valve, that is located behind the fuel tank may be bad. It is part of the EVAP system. IIRC it has two big hoses going to either side of it, then a small vaccum hose going to a nipple on the top, and then one more large hose connected to the bottom of it. The inner rubber diaphragm is made of thin rubber, and can tear after some time, espeically if you are boosted. I had a pesky CEL for a while too relating to the EVAP system, and after removing the valve from the car and taking it apart it was obvious. Although it looked unscathed from the outside, once I took it apart it was obvious the inner diaphragm was in fact torn.
Check it out, its worth a shot..
1999 Eclipse GS Built motor Hahn 16G Turbo w/ FMIC Hahn Stage 5 Portfueler (270's & 500's) Zeitronix Zt-2 wideband w/ 3.5bar MAP 3" SS Turbo Back CM Stage 4 Clutch and Fidanza Flywheel Baer Big Brake Kit
#127243, "RE: P1494 - Can't figure it out. Need the light off." In response to Reply # 1
Are you referring to PNC 05611H in this pic? If so I guess it could be leaking causing there to be insufficient vacuum to the LDP and not letting the diaphragm move, though I was under the impression the roll over valve hardly ever malfunctioned. Do you remember if you had to drop the tank to get to it?
Oh, and the LDP (Leak Detection Pump) is PNC 05629 in the pic.
#127244, "RE: P1494 - Can't figure it out. Need the light off." In response to Reply # 2
Yes, that is the exact part I am referring to. It has been debated whether or not boost causes this part to malfunction, but I can tell you with absolute certainty that it does. The inner thin rubber diaphragm is only meant to see vacuum pressure. It sits on a shaft that has 4 protruding sides to it for rigidity, like a cross pattern. When the diaphragm sees boost and flexes the opposite way it is designed to, towards the four sided shaft, the square edges of the shaft eventually wear it down and will tear it. When this happens the seal is shot and you will throw codes for an EVAP system leak. It happened to me, and as soon as I diagnosed the problem and replaced the valve, the CEL went off and has not come back on since.
You do not have to drop the fuel tank. Just jack up the back of the car and you will see the valve situated right behind (towards the back of the car) the fuel tank. Pull it out of its clip, remove the four hoses, and replace it.
