ML 320 Check Engine light Help - Mercedes-Benz Forum

 
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post #1 of 9 (permalink) Old 05-06-2011, 03:52 AM Thread Starter
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Question ML 320 Check Engine light Help

I own an 2002 Ml320 that has a check engine light illuminating. I brought my Ml 320 to autozone and was told that the error codes were P0161 & P0158. Can anyone tell me the location of these Two sensors and what they mean? My only option now is to replace all four sensors, Yikes.
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post #2 of 9 (permalink) Old 05-06-2011, 07:26 AM
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I believe it is the left side post cat oxygen sensor. Both codes for just the one sensor. They can be purchased from autohausaz. I would also post this on the w163 forum. Mostly because one of the codes is for a high voltage. I am not sure why that would be the case but someone on the w163 forum will know. If you do end up changing that sensor, it is very simple. Do it when the vehicle is cold! I spray some PB blaster around the threads to loosen things up. Unplug the wire and unscrew the sensor. I think it is 17mm....maybe. That put in the new sensor and plug it in. Seems like the pre cat sensors are the ones that have a metal housing of sorts that also need to be unbolted. It has been a couple of years since I replaced O2 sensors in a w163 but if memory serves me correctly, that is about it. Dont forget to clear your codes after. Either take it to Advanced Auto, get a OBDII scanner and do it, or undo the negative terminal of the battery for a few minutes. For the latter you will need your radio code afterwards.

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post #3 of 9 (permalink) Old 05-06-2011, 08:44 AM
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It's not likely the oxygen sensors but rather the MAF sensor.

MAF creates bad mixture that O2 sensor can't handle, generating O2 sensor code.

MAF sensors fail on all M112/113 engines, and if yours hasn't been replaced yet it's probably time.

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post #4 of 9 (permalink) Old 05-06-2011, 09:38 AM
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On the top of General section here you will find stickies with codes explanation:
P0158 O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)
P0161 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
As previous replies indicate -the codes show the results, not the problem itself and need to be interpreted.
Unfortunately interpretation based on 2 codes is having big margin for error. When MAF sensor went bad on our ML320, it triggered 10 codes, while the truck was running still without symptoms.
In this case, not knowing actual mileage I would start with O2 sensor. They are due to replace at 100k miles, so if that is what the truck has, I would replace all of them.
MAF sensors don't wear out like O2 sensors. They just fail occasionally and there is no mileage set when they do, so replacing it would be my second choice.
On other hand after replacing MAF on our E320 (same engine) the mpg went up by almost 15%, so it might be worth buying new MAF and try it. If the old MAF is good, than you will have spare one, what is not a bad thing.
If you don't have scanner to erase the codes after repair, they should clear themselves after some driving. In case of MAF replacement I had to restart the engine 7 times to clear CEL- 10 seconds job.

Last edited by Kajtek1; 05-06-2011 at 09:53 AM.
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post #5 of 9 (permalink) Old 05-06-2011, 10:41 AM
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Just swap the sensors. Right to left, left to right. If the CEL code changes to bank 1 sensor 2, it's that O2 sensor that's bad.
Don't forget anti-seize compound when installing used/new sensors.
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post #6 of 9 (permalink) Old 05-06-2011, 02:43 PM Thread Starter
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Check engine liight

Thanks for all of the suggestions, My ML is has 102,000 miles on it so im going to bite the bullet and replace all four sensors. to be continued.
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post #7 of 9 (permalink) Old 05-07-2011, 09:23 AM
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Quote:
Originally Posted by Divine View Post
Thanks for all of the suggestions, My ML is has 102,000 miles on it so im going to bite the bullet and replace all four sensors. to be continued.
Still, after you do that you'll be installing a new MAF sensor.

Kent Christensen
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post #8 of 9 (permalink) Old 05-07-2011, 10:39 AM
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Originally Posted by lkchris View Post
Still, after you do that you'll be installing a new MAF sensor.
At 102K he probably already has.

Divine, if you are doing the work yourself, the least-costly alternative is to buy the Bosch universal ones. All you replace is the actual sensor, so you use part of your old wiring and the connector from your existing sensors. That way you can save a bit of money. But if you're paying someone to do the work (or don't want to mess with it either way) then buy the direct-fit replacements.

Either way I would strongly encourage you to use OEM Bosch replacements and to get the part numbers by visiting their USA site and using the parts finder. The online vendor catalogs can be difficult to digest and the Bosch parts finder is always accurate. Once you have the part numbers you can then search for them at your favorite vendor, such as autohausaz.com, rmeuropean.com, etc., and yes, even Amazon.

Now all of that said, before you do anything else, I would crawl under the truck (support it safely!) and check to be sure the wiring didn't get snagged by anything. Locate the sensor (it's pretty obvious, it sticks out of the exhaust pipe) and trace it back to where it plugs in. Unplug the connector, make sure it's clean and dry (there is a connector that can seep AT fluid, that could create issues as well) and if it all looks fine, then you know the sensor is going flaky on you.

Good luck.

Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy; its inherent virtue is the equal sharing of misery. (Winston Churchill)

Last edited by Check Codes; 05-07-2011 at 10:41 AM.
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post #9 of 9 (permalink) Old 05-11-2011, 09:50 PM Thread Starter
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Thanks Gregs210 planning on checking that out, appreciate your suggestions.
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