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Mike V.
Mike V., Nissan Technician
Category: Nissan
Satisfied Customers: 25164
Experience:  Nissan factory trained and Certified Subaru Technician.
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Nissan Altima: Timing chain..leaks..oil every..about 1quart (Cab miles

Customer Question

Nissan Altima 03, 2.5L. Timing chain cover leaks, mostly from the top. I'm loosing oil every week, about 1quart (Cab miles 300 plus a day). I got a code about a possible vacuum leak. Could this leak cause presure loss to warn about vacuum leak? If so,how hard is it to remove the cover to reseal it and are there any parts that wear out to replace during the take apart, do I need to retime/replace timing chain at all. Please help, thanks.
Submitted: 7 years ago.
Category: Nissan
Expert:  Mike V. replied 7 years ago.
Hi there! Do you have a specific code?
Customer: replied 7 years ago.
Troubleshooting P0420 Catalyst system efficiency below threshold bank 1. Probable cause, 1. LARGE VACUUM LEAK 2. FUEL SYSTEM FAULT 3. IGNITION SYSTEM FAULT 4. FAILED BANK 1 CATALYTIC CONVERTER. I have already changed the cat 2yrs ago and something to do with ignition system (crank sensor). So my guess is the vacuum leak because I have been getting high idle code in the past but when nissan reprograms it, it works fine for just a month or so since then I have just been ignoring its. Hope that helps some in determining the problem.
Expert:  Mike V. replied 7 years ago.
OK, it is possible that it is a vaccum leak,however the code is more likely there because the car is using oil so it hurst the converters ability to store oxygen. I would pull the front pip down and take a look at the converter itself, make sure the catalyst isn't broken up inside.
As for the question about the timing chain cover, these can be a bear to do. You will have to drop the upper oil pan as well to access 2 bolts that come from the bottom into the oil pan.
As for the timing chain,there is really no need to replace anything as long as there is no noise or check engine light on with a timing chain code.
Even though you are leaking oil,these are noted for using oil ans well so I would really look closely at the converter.
I do not believe a vaccum leak would cause the car to leak oil,and it could be an issue with the throttle body causing the high idle.
Hope some of this helps! Please reply if needed! Thanks