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1984 MB 380SL, 1988 MB 560SL, 1983 MB 300CD, 1984 MB 300SD, 1985 MB 300
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126 Posts
Discussion Starter #1
The check engine light comes on when I start my 89 560SL (74,0000) in the morning. After it heats up to normal, I turn the car off and the light does not come on again. It has been this way for about a month. What is likely turning on the light and why would it go out after restart (once engine is hot)? O2 sensor not right? Thanks!

Richard
 

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1988 560SL (California Model)
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5,104 Posts
A possibility. An Italian tune-up can fix a number of problems. Buy a couple of bottles of Techron (Walmart, Chevron) and dump it in the tank...then fill it up with premium. Now the fun part. Take her out on the highway and run the snot out of her. Least an half hour. Worth a try before starting to throw money at the problem. Let us know.

From the owner's manual. If the lamp comes on when the engine is running, it indicates a malfunction of the 02 sensor on federal version vehicles, and injection system or emission control system on the California version vehicles.
 

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1984 500SL 000760
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509 Posts
could be be a Heated 02 sensor that is not heating electrically but is heating up from the exhaust gases passing by it. I am not familir with the 89+ model is there a ODB port or a ecu/jetronic type light that flashes an error code so you can count the flashes and check the code? Alot of parts stores will read teh code for you for free if it has the OBD port.
 

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'88 560SL, '19 AMG E53 Cpe, '15.5 Volvo XC60, '53 MG TD, '35 Ford Cpe and a few more
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220 Posts
Our '88 CA-spec 560SL has a terminal strip on the drivers side fender under the hood that flashes a fault code for the OBD 1 system if you jumper two terminals. I don't recall the protocol. It also works for the SRS system.
 

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1975 450SL
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2,440 Posts
In my research related to the pending Megasquirt conversion, I've learned a lot about O2 sensors, and this sounds like yours could have gone to the Happy Hunting Ground. They're not really difficult to change, you just need to get a new one, and get a wrench on the old one. However, they do tend to weld themselves in with age, heat cycles, and exhaust residue. If you don't have requisite BFW (Big F*****g Wrench), and don't want to buy one, you might be able to 'farm it out' to an exhaust shop.

Just an idea from over here, over the internet.
Scott
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,166 Posts
In my research related to the pending Megasquirt conversion, I've learned a lot about O2 sensors, and this sounds like yours could have gone to the Happy Hunting Ground. They're not really difficult to change, you just need to get a new one, and get a wrench on the old one. However, they do tend to weld themselves in with age, heat cycles, and exhaust residue. If you don't have requisite BFW (Big F*****g Wrench), and don't want to buy one, you might be able to 'farm it out' to an exhaust shop.

Just an idea from over here, over the internet.
Scott
Be advised... Replacing will not extinguish the light if it has tripped. The "sensor" on the side of the speedometer/odometer, is a one-time use. Permanent fix is to remove the bulb... :)
 

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1988 560 SL
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1 Posts
Check engine light came on in my recently acquired 1988 560SL. The car had sat for quite a while and seems to run fine,but with a slight hesitation off line. I am familiar with Italian time-ups as I also own an XJS Jaguar. How does one read the engine codes,and clear them.
Hopefully fresh gasoline and a herd run will work wonders.
The former owner said the local dealer cleaned the air flow resister? Some years ago when the check engine light came on
Any suggestions would be appreciated
Tom Wilson
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,512 Posts
Check engine light came on in my recently acquired 1988 560SL. The car had sat for quite a while and seems to run fine,but with a slight hesitation off line. I am familiar with Italian time-ups as I also own an XJS Jaguar. How does one read the engine codes,and clear them.
Hopefully fresh gasoline and a herd run will work wonders.
The former owner said the local dealer cleaned the air flow resister? Some years ago when the check engine light came on
Any suggestions would be appreciated
Tom Wilson
You didn't mention mileage. Seems to me that the light comes on:

A) if you have an 02 issue
B)at 100,000 miles it comes on automatically to remind you to replace the 02 sensor.


Light bulb only comes on once in it's life........and needs to be removed to "clear" the code....permanently.



Please correct me if I misspoke. I don't have an 02 sensor....so I really haven't paid that much attention.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,347 Posts
You didn't mention mileage. Seems to me that the light comes on:

A) if you have an 02 issue
B)at 100,000 miles it comes on automatically to remind you to replace the 02 sensor.


Light bulb only comes on once in it's life........and needs to be removed to "clear" the code....permanently.



Please correct me if I misspoke. I don't have an 02 sensor....so I really haven't paid that much attention.
That is what I had heard but later learned that the 560SL is different. It shows an actual O2 sensor failure and once replaced it should clear and the light go out.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,512 Posts
That is what I had heard but later learned that the 560SL is different. It shows an actual O2 sensor failure and once replaced it should clear and the light go out.
Or you can do what my neighbor did in his 90s Ford 150.....piece of black electrical tape over the dash light....clears the annoyance.
 

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1988 560SL (California Model)
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5,104 Posts
Or you can do what my neighbor did in his 90s Ford 150.....piece of black electrical tape over the dash light....clears the annoyance.
That's what I did with the SRS light (no airbag) and the bulb warning light. My headlight relay system triggered that. Eventually I will get around to pulling both bulbs.

Rowdie is correct about the check engine light on the 560SL. Mine did not come on at 100,000 miles. Ended up changing it out anyway about 4,000 miles later. No failure or light...figured it was about time.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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7,166 Posts
That is what I had heard but later learned that the 560SL is different. It shows an actual O2 sensor failure and once replaced it should clear and the light go out.
Uhhh... Damn. Contrary to what I have understood. Hmmm...
 

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1998 SL500, 1959 220S, 1970 280SL
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777 Posts
The 560 will turn the CEL on for a variety of faults. The fault is indicated by the number of blinks on a tester hooked to the diagnostic socket on the right side of the car by the firewall.

It's the 380 that turns the light on at a specified mileage.
 
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