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Old 09-14-2008, 10:57 PM   #1 (permalink)
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1992 500Sl Check Engine light comes on

I have a 1992 500SL. the check engine light came on recently. I disconnected the battery for 5 minutes and the light went away. After 100 miles and a couple of weeks later, the check engine light came back on. Can someone kindly advise me what to do please.

I have a 16-pole diagnostic connector: do I read the codes by first shorting poles 1 and 3, and then connect the LED light between poles 3 and 16?

And do I read the second code by repeating this procedure ?

Thanks.
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Old 09-15-2008, 02:13 AM   #2 (permalink)
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Quote:
Originally Posted by 1992500SL View Post
I have a 1992 500SL. the check engine light came on recently. I disconnected the battery for 5 minutes and the light went away. After 100 miles and a couple of weeks later, the check engine light came back on. Can someone kindly advise me what to do please.

I have a 16-pole diagnostic connector: do I read the codes by first shorting poles 1 and 3, and then connect the LED light between poles 3 and 16?

And do I read the second code by repeating this procedure ?

Thanks.
Hi 1992500SL I can't remember if in 1992 there was already the MAF sensor in your car so I might be wrong but all the symptoms lead me to think that your MAF is going to need to be replaced.
Please someone correct me if I am wrong.

Hope this helps tho.

Cheers.
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Old 09-15-2008, 05:07 AM   #3 (permalink)
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Originally Posted by 1992500SL View Post
I have a 16-pole diagnostic connector: do I read the codes by first shorting poles 1 and 3, and then connect the LED light between poles 3 and 16?

And do I read the second code by repeating this procedure ?
Connect the LED first and leave it connected. Short #1 to #3 for 3 seconds and count the blinks. Short again for 2 seconds to read the next code, or short for 7 seconds to erase the one just read.

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Originally Posted by msbarsi View Post
Please someone correct me if I am wrong.
No MAF in this car.
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Old 09-15-2008, 07:20 AM   #4 (permalink)
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I had a recurring CEL in my '92. Reset and it was ok for about two weeks. Then it was back. I was on my way to expensive parts replacements and diagnostics when my indy found a cracked vacuum line. By the time it was over, all the vacuum lines were brittle and cracked. This caused lots of vacuum leaks and the CEL. Vacuum lines are cheap and easy to replace.
There is also a modulation valve on your smog pump. Replace it as it may also contribute to the problem.

No more CEL for the past year.
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Old 09-15-2008, 11:34 AM   #5 (permalink)
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Bob,

Since I have disconnected the battery and the check engine light went away, am I correct to say that the code(s) is gone and I will have to wait until the check engine light comes back on again before I can read the code ?

Also, If a vacuum line is "open", the idle should go up, right ? but my rev stays quite steady at 600 rpm, give and take.

In my Volvo, a new fuel cap always solve the check engine light problem. Do you think a new fuel cap might help too ?

Thanks,

Alex.
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Old 09-16-2008, 09:21 AM   #6 (permalink)
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Vacuum lines affecting idle

My broken and cracked vacuum lines did not affect idle. I was also steady at 600 rpm. You have a 16 year old car just like mine. Those lines are plastic. Unless they have been replace already, the engine heat alone has deteriorated them to egg shell consistancy.
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Old 09-16-2008, 11:05 AM   #7 (permalink)
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Roadking,

Yes I need to check all the vacuum lines. They were all replaced a couple of years ago but because my radiator is old, my car is constantly running between 100C to 105C which would make "egg-shell" much quicker. I am having the radiator replaced this weekend.

Going back to the vacuum lines, did you open all the plastic covers and visually check them, or did you use a tool to check.

Thanks,

Alex.
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Old 09-16-2008, 03:02 PM   #8 (permalink)
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We used a tool. we hooked each up to a hand vacuum pump with a gauge. Pump a couple times and hold. If the vacuum decays you have a bad line.

If you replaced them all, you may want to have your indy check the vacuum modulator on you smog pump. It is along side the pump on the lower right hand side of the engine. There are a couple of rubber hoses that attach it. They can also go bad.
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Old 09-17-2008, 12:47 PM   #9 (permalink)
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Roadking,

Great, will check this weekend along with the radiator replacement.

thanks.

alex.
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