My check engine light has been on, and I just found the fault codes (thanks to the help of many of you on this site), and it is most likely that I need to change the sensor(s). To my understanding there is an upstream and downstream sensor.

My car runs well, no hesitations, no startup issues, and no noticable loss of gas mileage. Do I need to change both sensors, or should I just do it anyway (ie. is one more likely to be the culprit)?

I am inclined, with 98k on the car, to just replace them both, is this a smart move?

Finally, I have been looking for sensors and noticed that I can get universal sensors for up to less than 2/3 the price of OEM. The universals require splicing, etc... Should I go with OEM fits, or will the universals do the same job? Also, I noticed brands like Bosch have both universal and OEM, which makes me wonder if the only difference is the "exact fitting" vs. splicing fits. So, if I get a universal, will it do the same job as the OEM, as long as it's installed correctly?

Thank you.

Again, you are using info for a 210 E320 w/OBD2 instead of a 124 chassis E320.
Your car is a 124.032 w/OBD1 and it does not have downstream sensors..it has one 4 wire sensor.
And looking at your codes . I would check the 12v to the sensors heater and the heaters coil before doing anything b/c that is what your codes indicate.

You have a 1995 E320-124 chassis. Here is what you have:

http://catalog.peachparts.com/ShopByVehicle.epc?q=1995-Mb-E--3--0--Sedan-Fuel--Injection&yearid=1995%40%401995&makeid=MB%40%40MB%40%40X&modelid=E%2D320%2D001%40%40E+320+Sedan&catid=C%40%40Fuel+Injection&subcatid=C5010@@Oxygen+Sensor&mode=PA

Here is the sensors for a 1996 E320. That is a different chassis , even tho it is still a E320. Notice it is not a 124 chassis, but a 210.
Always mention your chassis when asking questions on E320 [ or year] b/c they are very different in many ways. Like 02 sesnsors.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1996-Mb-E--3--0--Sedan-Fuel--Injection&yearid=1996%40%401996&makeid=MB%40%40MB%40%40X&modelid=E%2D320%2D002%40%40E+320+Sedan

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A Dalton

Not sure what Arthur thinks but Doc once wrote that Bosch universals are fine for OBDI cars. You just have to check the price of both and see if it's worth it to you. It's located on the top of the exhaust pipe pretty much right underneath the console with the wiring going into the passenger footwell / 22 mm open end wrench.

The jury is still out on Uni sensors....but the Bosch replacement seem to be OK.
.........here is the rub with the UNI sensors when used on the 124.032 HFM/SFI sytems [ The posters chassis , by the way]..

When one gets an 02 sensor code COUPLED with an AIR code on this system, [ the posters condition, by the way] , it indicates that the 02 sensor is no longer capable of attaining the extra lean [ low voltage ] readings required by the ECU self test for the AIR sustem. The AIR system uses the 02 signal to monitor the working of the AIR system. The ECU sends a self test signal to the AIR system when the cars coolant temp is up and it then looks at the 02 sig to see if the exhaust goes extra LEAN. If the report does not come back as such, then the DM [ led/sw N59 module ] brings on a code to notify the driver by popping the CE lamp and an AIR code #4. . So, is the AIR sustem not coming On and operating as it should ??? ..OR ..is the 02 not detetcting the extra lean condition cause by the AIR system activation..???
Now , if the other code is 2 , then we have a suspect 02 sensor heater circuit, which will not only pop an 02 code, but it will be coupled with an AIR code , even tho there is nothing wrong with the AIR system.
So. those who know these sysytems start their diagnosis with the LONE 02 sensor of this system by checking both the heater circuit of the sensor and the V readings of the sensor.

The problem w/uni sensors is many are not capable of the extra low readings required to monitor the AIR system and some will still bring On an AIR code right our of the box.

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A Dalton

Mr. Dalton, I have read a lot of you on this site already, so I'm a little intimidated to ask you, "are you sure?"

I have a 1995 e320 Sedan. My understanding is that it is a 124, and the codes I used are from another Thread, saying #2 is the Heated Oxygen Sensor, #4 Air Injection System faulty hot film mass air flow sensor with hot wire, and #26 Upshift Delay Faulty.

This was read off a 16-code box (indicates 124?) with the reset and little light, by pins 2 and 4 (if I recall correctly) right by my battery, as you told me in an earlier response. I cycled this 3 times to be sure my reading was correct, and each time it was 2, 4, then 26.

So, when I look up the part on-line and calling parts stores, both indicate that there is an upstream and downstream sensor? Some even said, front and back.

I am a genius when it comes to computers, but a complete moron when it comes to this stuff, I think I know how you feel, so I appreciate your patience with me.

>

No..I am just guessing........

Have you read any of my tutorials and postings on 124.032/124 chassis HFM/SFI Engine Maagement Sytem Dagnostics ??????

Are you aware of the inter-ralationship of an O2 sesnsor code 2 and a code 4 AIR system code on a 124.032 chassis ????
A very common diagnostic combo, I may add...............

Your code 26 is upshift delay and another common HFM/SFI code.

Let me assure you I am SURE ...........

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A Dalton

I remember once when Arthur made a mistake, so theoretically it could happen again.

For sure ..

But I am confident in my understandings of the mentioned chassis and how many sensors a 1995 E320 /124.032 HFM/SFI chassis has .................

..and I went to the extra trouble to post and list all that info/site /part # search/etc. for those who doubt it.
Go back and reread post # 2, where I direct all to the sensor info for BOTH the posters 124 chassis and the included 210 chassis dual sensor page.... just so we are perfectly clear on the differences of the two chassis 02 sensor/s arrangement. OBD1 [ 124/E320] used one 02 b/c they did not monitor after the CAT. That is main function of the second downstream sensor of OBD2 systems . [ 210/E320]

If one doubts a posters answer, just go to the Archieves... The info is all in there for confirmation and comparison ..some correct , some not. ... and the parts are available at the top of the page
My informational explaination of the common mistake made by newbies on the two chassis has been explained. The E320 has always created confusion on many postings [ as we all know] , so that is the main point of both this and my other response to his other posting. 124 and 210 are NOT the same car. They are just both E320 designations.
Anyone posting for E320 info here will be far ahead to mention which one they have if they want a correct response.
When we commonly respond to such a post with "year/model" , it is not a smart-ass response ..it is a mandatory question before we can give out any correct info b/c we know the differences...unless we just assume/guess which chassis..which I have learned not to do..........if there were not as many differences in the two chassis, it would not be of importance to the diagnostics...but there is a difference. So , a simple year or chassis would and will do just fine.............
Done.

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A Dalton

I have to add: If you change parts, without first knowing if they're bad, you're introducing an additional variable into your diagnostic (old vs new). In pure diagnostic routines, this is exactly the opposite of what you want to do, you want to isolate the symptoms with the least number of variables. Test first, replace later. Typically more economical also.

Second, in the diesel forum where I usually dwell, we all put our cars' year and model in our sig lines. This helps readers to understand what cars we have direct experience in, and also helps readers to see what year/model we might be discussing without having to scan back to the OP each time (especially in long threads). Just a suggestion which probably belongs in a different thread, ...

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Gone to the dark side

- Jeff

Thanks for that info, you can see that my car info is there now!

The world is a better place Gunth!

Any new info on your symptoms?

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Gone to the dark side

- Jeff

Mr. Dalton, will you check my new thread under Tech Help, 95 e320 Transmission Slipping? Help by Gunth Today 09:58 PM? (8-26-09) You gave me lots of info before and I hope you can do the same for this problem I'm having. Thanks.

Many thanks to AD for the O2 troubleshooting instructions on the first page.

I've had an intermittent check engine light on my '95 W124 E320 with a DTC code of 2 each time it would come up. I checked the wiring connections per the instructions and the connector had some noticeable corrosion. After cleaning both sides up, I get about 3ohms for the heater resistance (vs the 6-10 ohms specified) and did not get any voltage on pins 1 or 2 with the key in the on position. I don't get any voltage with the car running, either. No visibly worn wiring in the area.

Any other places I can check to verify that the O2 heater circuit is being powered appropriately? Can I check a certain pin on the ECU? A quick review of the fuse box reveals no blown fuses.

Well, I guess no one knows.

I'll add some additional information for posterity. An addendum to my notes and to Aurthur Dalton's instructions on the last page, the factory WIS indicates that the car needs to be idling for at least 2 minutes and have coolant temps > 80c when checking for voltage on the heater circuit. I didn't meet these criteria last time.

Under the right test conditions, I do have voltage on pins 1-2, good connection to the O2 harness itself, and 3-4 ohms of resistance on the O2 heater sensor itself. I still recently got the check engine light on a 1-hour trip. If it comes back after this latest test, I'll replace the O2 sensor on the assumption that the heater resistance is just a little too low and is falling outside of the desired test parameters.

I always clean O2 sensors with carb cleaner,let air dry,airflow sensors I use the plastic safe.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt