Downstream O2 Sensor Technical Assistance Needed
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ML550
Downstream O2 Sensor Technical Assistance Needed
This one has me baffled. I extended my downstream O2 sensors in order to use them with the cats on my MBH mid-pipe set-up. Everything worked great for about three or four weeks until I took my car to the dealer to have some items fixed prior to the expiration of my extended CPO warranty.
When I picked the car up, I had an illuminated "check engine" indicator. Service writer said it was due to cross-threaded O2 sensor and that they could reset it, but that it would come right back on.
So I get home and get out the multiplexer and start up DAS to read out the faults. I get a message that there are shorts in the downstream O2 circuits. So now I'm thinking the tech disconnected the small aftermarket cats and let them hang from the wires, causing my extension connections to fail. So I redo the connections, it's all good, and now I get nothing but P0140 and P0160 codes, meaning there's no activity being read from the rear sensors.
I'm thinking there must be fuse that blew as a result of the temporary short that controls this circuit, but I'll be darned if I can determine which fuse it might be. I checked out the fuse diagram for the fusebox in the engine compartment, and it shows f43 and f63 being associated with the ME-SFI unit, but both appear to be good.
Does anyone have a clue whether the O2 heater circuit (or signal circuit, for that matter) is fused, and which fuses I need to be looking at.
Help needed!
When I picked the car up, I had an illuminated "check engine" indicator. Service writer said it was due to cross-threaded O2 sensor and that they could reset it, but that it would come right back on.
So I get home and get out the multiplexer and start up DAS to read out the faults. I get a message that there are shorts in the downstream O2 circuits. So now I'm thinking the tech disconnected the small aftermarket cats and let them hang from the wires, causing my extension connections to fail. So I redo the connections, it's all good, and now I get nothing but P0140 and P0160 codes, meaning there's no activity being read from the rear sensors.
I'm thinking there must be fuse that blew as a result of the temporary short that controls this circuit, but I'll be darned if I can determine which fuse it might be. I checked out the fuse diagram for the fusebox in the engine compartment, and it shows f43 and f63 being associated with the ME-SFI unit, but both appear to be good.
Does anyone have a clue whether the O2 heater circuit (or signal circuit, for that matter) is fused, and which fuses I need to be looking at.
Help needed!
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From: New Cumberland, PA
ML63
I would guess O2's are bad now, and it's not fuse related or relay related.
If it didn't have a light going to the dealer and they do work on the car, and now the light is on I would ask them for something.
If it didn't have a light going to the dealer and they do work on the car, and now the light is on I would ask them for something.
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From: Valley of the Sun, Arizona
C63, SL55, E55, CLS55, ML63, C55
I will say this, this cat issue with komp55's car is strongly making me consider if I want to even offer cats. Reason 1) I'm not the biggest fan of the cats I use. 2) leaning towards more of an off-road mid-section.
With that said, Extending the o2 wires should happen on the harness side. The o2 sensor wires themselves should not be cut then spliced back together.
IIRC, by the transmission's bell housing you will see where the o2 wire plugs are. just before the plug there are some wires that go into the plugs. This is the wire that should be extended if it is needed. Not the o2 sensor wire itself.
On that note I have been made aware of the o2 sensor issue when using cats on the 55k. We will work coming up with a fix for this very soon so people will not have to extend the o2 sensors when using cats. If this involves ditching the cats, or making a chance. We will explore every option.
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ML550
Extending the wires before the harness connectors may be the answer, but Bosch makes a specific univeral O2 sensor replacement (part #15733) that is applicable to both the upstream and downstream O2 sensors and is shown as specifically fitting the W211 E55. The kit includes a well engineered connector to splice O2 wires together. I used two of the universals when repairing my O2s. Before that, I had soldered in some O2 wire to lengthen the O2 wiring using the original #16328 downstream O2 sensors - and that set-up worked perfectly and threw no codes until the dealership worked on the car (trust me, this O2 problem is minor compared to having my engine's rear crank seal replaced under warranty 
). That said, Bosch advises against soldering wires together stating that it will shorten the life of the sensor (that was printed on the instructions to the universal O2 kit).
So I guess my next diagnotic step is to hook up the Midtronics power supply to the battery, turn the ignition switch to position 2, turn off the electrical consumers (e.g., radio, HVAC, auto-headlights, etc.), raise the car on the lift, and then measure voltages at the O2 sensor connectors. At least that way I'll know if the problem is upstream (e.g., fuse - if there is one) or downstream - FU'ed O2 sensor or whatever. Before I have to go through this step, I'm still hoping someone knows whether or not there are any fuses protecting the O2 sensor wiring circuits.
). That said, Bosch advises against soldering wires together stating that it will shorten the life of the sensor (that was printed on the instructions to the universal O2 kit).So I guess my next diagnotic step is to hook up the Midtronics power supply to the battery, turn the ignition switch to position 2, turn off the electrical consumers (e.g., radio, HVAC, auto-headlights, etc.), raise the car on the lift, and then measure voltages at the O2 sensor connectors. At least that way I'll know if the problem is upstream (e.g., fuse - if there is one) or downstream - FU'ed O2 sensor or whatever. Before I have to go through this step, I'm still hoping someone knows whether or not there are any fuses protecting the O2 sensor wiring circuits.
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ML550
This will be my last resort if I can't get this sorted out. I have to pass an emissions test in a couple of months; otherwise I wouldn't really care if the downstream sensors are working or not; it's the front ones that control the mixture.
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From: New Cumberland, PA
ML63
What state are you in?
Who's file are you running on the car?
The O2 heater can burn themselves out not often but it can happen. I know in the drivers side relay box under the hood is where the relays are located for the O2's. I can look it up later. Also do you have SDS star? There is a simulation mode that can help you solve your issue with a visual aide.
Who's file are you running on the car?
The O2 heater can burn themselves out not often but it can happen. I know in the drivers side relay box under the hood is where the relays are located for the O2's. I can look it up later. Also do you have SDS star? There is a simulation mode that can help you solve your issue with a visual aide.
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From: Northern VA
W211
Komp55
Sorry to hear the issues you are having with the O2s. I was going to get my headers installed and find out MBH never sent the hardware for the headers (gaskets, copper nuts) that was included in the sale.
As far as the o2 CEL codes, i did purchase a set of o2 simulators from Bruce TTM to trick the ECU with readiness monitors. It worked on Lowprofiles car. So hope it works with mine when i do get the headers installed!
Sorry to hear the issues you are having with the O2s. I was going to get my headers installed and find out MBH never sent the hardware for the headers (gaskets, copper nuts) that was included in the sale.
As far as the o2 CEL codes, i did purchase a set of o2 simulators from Bruce TTM to trick the ECU with readiness monitors. It worked on Lowprofiles car. So hope it works with mine when i do get the headers installed!
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ML550
As for the header mounting hardware, I didn't know it was supposed to be included with the MBH headers.
It's readily available from all MB dealers and the usual online parts sources. You'll want to have on hand:
16 272 990 00 05 studs
16 112 142 00 72 copper lock nuts (M6)
8 112 142 01 80 manifold gaskets
When I did mine, most of the studs backed out with the lock nuts. It was easier just to install replacement rather than spend the time during the install to remove the locknuts from the original studs (although it can be done without much effort).
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From: Northern VA
W211
Perhaps when you redid the o2 sensors it secured whatever came loose from the MB Tech leaving them hanging. Hope i works out for you!!!
MBH in the header deal i got said it would come with it, but didnt. Got Pm that gaskets will ship out to me. Very frustrating to know that parts were missing when it was time to get the headers installed .
MBH in the header deal i got said it would come with it, but didnt. Got Pm that gaskets will ship out to me. Very frustrating to know that parts were missing when it was time to get the headers installed .
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From: Salt Lake City (but not Morm)
2003 E55 & 2014 GL550
Wish you had a spare heated O2 around. I say plug it right into the connectors and turn key on and check for heat. Least you would know right off bat if it was O2 or connection.
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ML550
I do and will do this if the light reappears. A little more of a simplistic approach than probing with the multimeter, but will at least let me know if the O2 heater circuit is getting voltage. Thanks for the suggestion.
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From: Northern VA
W211
Didn't get it done . Showed up at 8am but.couldnt work on it til 3pm waited for call to bring car back . Didn't get call til 5 and schedule for Saturday morning. But might be delayed since I have a valve cover ps leak that dealer needs to redo from last year
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Mercedes Benz E55 AMG
Did you ever figure it out?
