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Check engine light / oil cap off - connection?
Thread Starter
Instructor
Joined: Nov 2000
Posts: 192
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From: Egg Harbor Twp, NJ NJ
Check engine light / oil cap off - connection?
Got a solid engine check light yesterday and found my oil cap off sitting on top of the radiator cover. I must have failed to install it at the beginning of last week. Just a small trace of oil on the hood liner.
Would leaving the cap off cause thr engine check light?
Would leaving the cap off cause thr engine check light?
Melting Slicks
Joined: Apr 2003
Posts: 2,989
Likes: 10
From: Columbus OH
That's pretty big vacuum leak. I'm surprised the engine didn't run rough. Forgetting to replace the oil filler cap causes my M3s to run rough and they won't idle smoothly. Learned that the hard way.
Thread Starter
Instructor
Joined: Nov 2000
Posts: 192
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From: Egg Harbor Twp, NJ NJ
There is no noticeable engine roughness. In fact it seems normal. I feel lucky that very little oil splashed out. I'm not sure why it didn't, but there was only one small spot on the hood liner. No oil runnig down the block or on the fuel rail covers.
Thread Starter
Instructor
Joined: Nov 2000
Posts: 192
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From: Egg Harbor Twp, NJ NJ
And the answer is! Dealer says it was the oil cap not installed that set a PCV system code. I don't know the code number yet. Will post later.
There's $60 that I should have used torward an OBDII scanner.
There's $60 that I should have used torward an OBDII scanner.
Team Owner
Joined: Oct 2004
Posts: 27,420
Likes: 64
From: San Clemente CA
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Thread Starter
Instructor
Joined: Nov 2000
Posts: 192
Likes: 0
From: Egg Harbor Twp, NJ NJ
Code P0171 was set in my case. Manual dicription says "If the PCM detects an excessively lean condition, DTC P0171 or P0174 sets."
Not sure why the missing oil cap creates the lean condition.
Not sure why the missing oil cap creates the lean condition.
Safety Car
Joined: Jun 2004
Posts: 3,563
Likes: 2
From: Dallas Tx
If if was run for a while, I'd change the oil.
Normally the pcv system contols the air volume entering the intake via the pcv system orifice. The AFR calculations account for this small amount of air. When it is uncontrolled, much more air is entering and the engine is now running lean.
Last edited by Michrider; Jan 13, 2009 at 11:12 AM.
Thread Starter
Instructor
Joined: Nov 2000
Posts: 192
Likes: 0
From: Egg Harbor Twp, NJ NJ
Unmetered (also unfiltered) air entering the engine. The O2's pick up the extra air/lean condition and try to richen up the fuel trim. I've seen that P0171 on several cars where it was driven with the oil cap off. Put the cap back on and drive for a couple days and the code will clear itself when the O2s no longer see the lean condition for a couple of drives. No need to reset with a scanner/dealer, just drive it with the cap back on.
Now that makes sense to me - thanks. And I did have the oil changed yesterday.
Now that makes sense to me - thanks. And I did have the oil changed yesterday.
Thread Starter
Instructor
Joined: Nov 2000
Posts: 192
Likes: 0
From: Egg Harbor Twp, NJ NJ
Unmetered (also unfiltered) air entering the engine. The O2's pick up the extra air/lean condition and try to richen up the fuel trim. I've seen that P0171 on several cars where it was driven with the oil cap off. Put the cap back on and drive for a couple days and the code will clear itself when the O2s no longer see the lean condition for a couple of drives. No need to reset with a scanner/dealer, just drive it with the cap back on.
If if was run for a while, I'd change the oil.
Normally the pcv system contols the air volume entering the intake via the pcv system orifice. The AFR calculations account for this small amount of air. When it is uncontrolled, much more air is entering and the engine is now running lean.
Now that makes sense to me, thanks. I did have the oil changed yesterday.
If if was run for a while, I'd change the oil.
Normally the pcv system contols the air volume entering the intake via the pcv system orifice. The AFR calculations account for this small amount of air. When it is uncontrolled, much more air is entering and the engine is now running lean.
Now that makes sense to me, thanks. I did have the oil changed yesterday.
Safety Car
Joined: Dec 2007
Posts: 4,070
Likes: 162
From: Coralville Iowa
Glad it's fixed - but it sure would have been a nice gesture if the dealer just reset the computer without charging you. That seems just a bit greedy to me - but I know they need the $$.
