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Q: My Check engine light is on and Napa, Dodge - Jeep service said that code P0455 on 1998 Dodge Dakota

Evap System Large Leak detected. Checked tank, gas cap, purge valve all not leaking.

BUT, tech said that Leak Detection Pump IS LEAKING INTERNALLY. Leak Detection Pump is expensive and is not mentioned at all as a cause of the P0455 code on your sight. Is this a simple problem that they are fixing by unnecessarily replacing an expensive part???? Thank you
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Be really hard to disagree with a tech that can test your vehicle hands-on! These pumps do give problems at times and if it is not working the vehicles computer can not complete the evap test, thus the trouble code. NOW, is it the pump for sure, we can't say for sure!
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Chrysler has been good about building tests into the systems, and the LDP is no exception. With a full professional level scan tool the system can be commanded to do a leak test right in the bay, and it can be commanded to run over and over again to facilitate testing. One strategy is to block off sections of the system when the test is commanded to run. By blocking the hose right near the LDP, the system should actually set a code and report that the system is blocked.(It pumps up too fast) Hose leaks are common on these in fact Chrysler sells the hoses as complete assemblies now, by blocking off sections a tech can prove where leaks are. (The same strategy of blocking sections applies when a smoke machine is used too) Some people try to do a smoke test and they don't realize that the canister vent valve is built into the LDP, and to close it there has to be vacuum supplied to the solenoid, and the solenoid has to be commanded on (scan tool or jumper wire) in order to have it pull vacuum on the diaphragm inside the LDP which rises up and that allows the vent valve to close. Incorrect diagnosis of a bad LDP are more likely honest mistakes because of a lack of understanding of the device. They can go bad, but its rare.
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