88' M103 (300SEL) CEL came on a couple of times today, then went off...?

[86560SEL]

Hi MB gang. Well, today for the first time, my CEL came on a couple of times and went off. First of all, the car is a 1988 300SEL with 154K miles.

First time was when I first left this afternoon, I let the car warm up for a couple of minutes- then pulled away. I got about .4 of a mile down the road to the main road and noticed the red check engine light illuminated.... thinking "this is just great", about .5 down on down the road, it went off and did not come back on during that trip. I went to the mall and was inside for a few minutes, came out, started the car and again - got about .2 down the road and the CEL came on and was on again for 1/2 a mile and went off and did not come back on.

Now, this is my 4th Mercedes, but the first time I ever had a CEL light issue, so not sure what to do. I am assuming that the light needs to come on and stay on before the testing would show anything? Also, where is the "diagnostics plug" on this car? Lastly, is this a car that I can simply take somewhere like autozone to get it checked, or is this going to be a MB-tech or dealer testing only? The car is running good and no different. I have read its common, but the only thing is that I have a splutter at idle. I am assuming it needs new plugs or ? I have read this is a common problem with these.

Sorry for being so clueless on the MB CEL's, but as mentioned, I am not familiar with them. Now if it was a CEL on one of our old 80s-90s GM cars, I could tell you in a second. I do not think there is a 1980s-1990s GM car on the road on which the check engine light is not illuminated. Our 98' Oldsmobile is one of them, despite testing and replacing parts they said it needed.

Thanks!

[Rocket]

I think you are correct in your statement about taking your vehicle to an MB specialist. Compared to todays vehicles the diagnostics are primative. There are a limited number of faults that will cause the CEL to come on and the most common are oxygen sensor failures. The lack of fault memory on these early vehicles makes diagnosis something that is best left to someone who has many years of experience in these vehicles. Seek out a shop in your area that has a technician or two that have been around the block, so to speak. I think in the end you will find that the failure is nothing thats very expensive to repair. Good luck.

[86560SEL]

Originally Posted by Rocket

I think you are correct in your statement about taking your vehicle to an MB specialist. Compared to todays vehicles the diagnostics are primative. There are a limited number of faults that will cause the CEL to come on and the most common are oxygen sensor failures. The lack of fault memory on these early vehicles makes diagnosis something that is best left to someone who has many years of experience in these vehicles. Seek out a shop in your area that has a technician or two that have been around the block, so to speak. I think in the end you will find that the failure is nothing thats very expensive to repair. Good luck.

Thanks - yes and now that you mentioned it, if I recall correctly, my old S-Class (1985 380SE) did not have a "check engine" light, but rather "o2 sensors" warning light in the same place where my check engine light is on the 300SEL.

Hopefully it is just something like a o2 sensor and hopefully they are not too costly on these cars.

[pawoSD]

I think a M103 O2 sensor is like $155ish......

[86560SEL]

Originally Posted by pawoSD

I think a M103 O2 sensor is like $155ish......

EEK. Sorry to hear its not priced like the o2 sensor on my old 89' Pontiac Safari wagon.... it was a whole $12.00.

Thanks for that info though.

[mbdoc]

You can get a Bosch universal 3 wire sensor for less than $70....

And that is the most likely issue that would turn on the CEL.

[86560SEL]

Thanks Doc.

Well, my car does have a pretty good exhaust leak somewhere in the exhaust system. Its not loud and I cannot smell exhaust while driving, but I can hear it splutter (like a leaky exhaust sounds) when it idles and I am outside of the car and wondering if this could have something to do with the airflow to the sensor or something?

I have never heard tell of it before, but just wondering.

I need to get that leak fixed soon anyway.

[mbdoc]

Unless the leak is from underhood?? That shouldn't have any effect on the O2 sensor.

[Chris Bell]

I have an 88 300 SEL also, While I was reading through I went to quickly check on the price of an O2 sensor...I noticed that there are two listed. Both are the same price, both made by Bosch but two different part numbers? Is there a difference between these two how do I know which one is correct for my car?

[johnathan1]

Does your car have the small black box with a red LED and a button on the frewall near the battery? If you hold down the button for 4-6 seconds, the LED light will flash the fault code(s). At least that's how my 89' 300SEL worked. My CEL would come on intermittently while driving, the problem ended up being a bad Air Mass Meter potentiometer.

[Arthur Dalton]

If your car is Cal version, here are the codes ..

FAULT CODE TABLE

DTC Readout Possible Cause of Failure
1 No fault found
2 Throttle position switch - wide open throttle fault
3 Engine coolant temperature sensor
4 Air flow sensor position indicator
5 Oxygen sensor
6 Not used
7 TD-signal (rpm)
8 Altitude correction capsule
9 Electronic hydraulic actuator (EHA)
10 Throttle position switch - closed throttle position fault (idle)
12 Exhaust gas recirculation temperature sensor

[86560SEL]

Originally Posted by Chris Bell

I have an 88 300 SEL also, While I was reading through I went to quickly check on the price of an O2 sensor...I noticed that there are two listed. Both are the same price, both made by Bosch but two different part numbers? Is there a difference between these two how do I know which one is correct for my car?

If its the o2 on mine, it will be the expensive one it needs. Thats just how my luck goes.

[86560SEL]

Originally Posted by johnathan1

Does your car have the small black box with a red LED and a button on the frewall near the battery? If you hold down the button for 4-6 seconds, the LED light will flash the fault code(s). At least that's how my 89' 300SEL worked. My CEL would come on intermittently while driving, the problem ended up being a bad Air Mass Meter potentiometer.

I will look on Sunday to see if it has that. 88-89 should be identical, but since yours was a California car and mine is a Florida car, it may be different in that aspect? I will look though. Thanks!

[86560SEL]

Originally Posted by Arthur Dalton

If your car is Cal version, here are the codes ..

FAULT CODE TABLE

DTC Readout Possible Cause of Failure
1 No fault found
2 Throttle position switch - wide open throttle fault
3 Engine coolant temperature sensor
4 Air flow sensor position indicator
5 Oxygen sensor
6 Not used
7 TD-signal (rpm)
8 Altitude correction capsule
9 Electronic hydraulic actuator (EHA)
10 Throttle position switch - closed throttle position fault (idle)
12 Exhaust gas recirculation temperature sensor

Mine was bought new in Florida, so would it have totally different codes?

[86560SEL]

Originally Posted by M.B.DOC

Unless the leak is from underhood?? That shouldn't have any effect on the O2 sensor.

Sorry, my "multi-quote" is not working....

No, I think its out about 1/2 way back, after the sensor, so I doubt thats it. Thanks!