Any suggestions would be greatly appreciated. The check engine light is on in my 1990 300TE and the idle is a little rough and low at around 500 rpm - sometimes it stalls too.

I purschased my new O2 sensor on ebay described by seller evalero1 as an "O2 OXYGEN SENSOR BOSCH SG497 MERCEDES-BENZ 300E L6 3.0" - the seller said it would "work great" on my car. This new sensor has four wires - two white (power / ground wires) and one black sensor signal wire and a grey wire for sensor ground. I have only 3 wires to re-attach this new sensor in my car. Two white and one black which I assume are the power / ground wires and sensor signal wire respectively.

I have attached the black wire from the car to black "sensor" on the new sensor and the two whites together too. I have tried switching the white connections around (just in case it matters) with no luck. I have left the grey wire on the new sensor unconnected in all attempts.

Can anyone give me some suggestions about what my problem might be and/or things to try next to solve this problem?

My first suspicion is the new O2 sensor from evalero1 is either broken or does not work in my car. If it does work, my second hunch is that maybe the grey wire does need to be grounded out on something? Third hunch is that the problem is not the 02 sensor at all. Any help is much appreciated.

Just one thing to add. I am considering myself successful when 1) the engine light goes off and the after that 2) the car idles evenly at closer to 1000rpm. Thanks again.

Bump... just in case!

what were the codes that you pulled?

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1994|040|W124.036|E500
http://www.mbworld.org/forums/image....ine=1216527951

A couple of things to try:

- try connecting the ground wire. Maybe this sensor needs it to be connected to work

- put a meter between the black wire and ground and see what voltage the sensor is putting out with the engine fully warmed up and running. It may be that the sensor is working fine, but something is causing the mixture to be rich or lean to the point where the computer turns the light on. If the mixture is in the ballpark, you would see something like .5V from the sensor.

If the voltage is low (lean) or high (rich), you can try to adjust it with a dwell meter or a meter with a duty cycle setting. There are dozens of posts on how to do this. But unless somebody screwed with the mixture, the problem is likely to be vacuum leaks, leaking injector seals, bad injectors, crud in the fuel system, etc.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

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When using a 4 wire sensor in place of aa original 3 wire , you have to be aware that a 4 wire heater circuit uses a seperate circuit..[which is the 2 white wires]
...so, in order for it to repalce the 3 wire , you have to hook one White to White , the other white to gray along with the gray [ ground], and Blk to Blk.
This will give you Blk for signal, gray for ground of both 02 and heater, and the other white for heater circuit feed .
The whites are not polarity sensitive, so either way is correct [ in other words , no +/- difference for heater white wires]

Thanks everyone. I will ajust my wiring and report back. Much appreciated.

How do you get the FI box cover off a W126, on the passenger side?

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.