G55K - Check Engine Light - O2 sensors - all replaced, car runs fine, light is still on

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Stuckmojo
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Hi All, 

 

I'm having this issue where the car shows the CEL and the OBD shows O2 sensors problem. Car runs absolutely fine. I have replaced all 4 sensors, and after a 40 min run the light comes back. Same error. 

A local (Dubai) indy has replaced the sensors with Denso - bought online. I read somewhere the issue may be with the connections going dry. 

I won't take the car to Mercedes here as they'll rape me. There's a really good MB indy but before I go to them I'd rather hear the forum experts' thoughts first.

Cheers

 

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Check the wiring for any open-circuit between the sensors and the Engine Control Unit.

With a multimeter, you can initially just check the DC resistance between connector pins (engine off) and see if its the same for both engine banks, for both the sensor connector side and the wiring loom connector side. If there is any discrepancy on the wiring loom measurements, do a full end-to-end check.

You can use a contact-cleaner spray, if you suspect dirty contacts, and try to re-seat the  mult-pin connectors on the ECU.

Also, the error may be a symptom of another problem, that leads to an out-of range lambda reading. this could be fuel or air related. Check that all cylinders are firing and that throttle and air-intakes are all working OK.

 

 

Pistonhead
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Reading Diagnostic Trouble Codes (DTC)  is like reading maps, it directs to a destination but not the actual address you want at that location; similarly the scanner reading oxygen sensor does not necessarily mean it is the sensor at fault.  After being directed to an area of possible fault it is down to the technician to fault find and diagnose at that location. 

The DTC has indicated oxygen sensors but the fault could lie with the wires feeding the sensors. Other related faults could trigger this fault such as exhaust leaks, inlet manifold leaks or worse case scenario anti freeze leaking into exhaust - this is a killer of sensors. So diagnostics have to test out sensors and eliminate the issue to getting it correct.

Having replaced all four sensors seems excessive. Did the OBD reading indicate which bank or for that matter which O2 sensor flagged up? If all four sensors flagged up; are you loosing coolant? In which case the anti freeze could be at issue here, but of course you are in Dubai; does not mean you are not using anti freeze, there must be a heat reducing agent in the coolant and block rust protection additives which may damage the sensors. NOW I am NOT claiming that this is the problem - it is a possibility which needs checking out. 

So diagnostics requires thinking out side the box; I am still learning this art and believe me a little knowledge can be dangerous; I have tripped that wire several times in my learning so far. 

Frankly, more information is required and this requires reading scanner values and if available use of graphing meter/oscilloscope to read patterns of Obehavior.

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Just remembered that these engines have the catalytic converters right-up near the exhaust manifold, with a sensor before and after the cat. Your problem may be related to a broken cat. Mercedes had issues will early failing cats in cars around Year 2000.

There is a sensor before and after the catalytic converter on each cylinder bank.

Changing all four sensors off the bat does seem to be a sledgehammer approach. Even a basic scanner should point to problems in a specific cylinder bank and then the sensors could first be swapped over to the other bank to see whether the fault follows the sensor.

As Rakesh said, just having a diagnostic scanner is not enough. The tech needs to understand your engine and all of its systems too. Also, the proper STAR diagnostics, as used by a dealer will tell you a lot more that a bunch of P codes that you get from a generic scanner. It also allows you to view real-time engine data so that you can see the actual reading reported by each O2 sensor. This, and other tests would help.

Car will run fine with broken cat (albeit with some risk of engine damage through resonant back-flow of ceramic particles from broken cat). Just your emissions will be out. However, normally you hear what sound like a tin can full of nuts an bolts rattling.

 

 

 

 

 

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Thanks both. 

Agreed on having the wrong medicine administered (4x O2 sensors).

Someone told me it's bound to be a dodgy connection. Cats look and sound fine, one never knows. 

As I said, the car runs perfectly. 

I'll just bite the bullet and take it to a local specialist who's working extensively on AMGs.

As far as I can tell (please correct me):

Best case scenario - dodgy connector/wiring

Worst case scenario - cat(s) or coolant leak (though the car has just been serviced with coolant flush and there were no losses)

 

Cheers

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Yes, you've correctly summed-up the possibilities.

Obviously. check out loose connector possibilities, but with 'proper' diagnostics equipment, the live readings from the sensors can be monitored and that will tell you easily if they are working or not. Else buzz through the wiring on the kOhm setting with a multimeter and compare readings from the wiring of the two cylinder banks.

Thing is, with a bad connection, you might expect it to be a bit more intermittent, but you say it all worked fine for 40 mins and then CEL on ever since?

Another quick way to check is to unplug the sensors, wiggle the cables a bit, then reconnect and see what happens.

 

Pistonhead
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Just a thought.

Has your problem occurred since the service - is the correct oil used in the engine?

This job need not cost an arm and a leg. Get a DTC reading and before any work is authorised question the garage as to what they have learned from the data streaming and will they do any test on any component to prove a fault component or are they just going to be replacing parts because the computer says so. If it is the latter find another garage.

If you are satisfied by the garage's reply and attitude to the diagnostics then go ahead.

Please inform us of the resolve.

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Hi, 

in answer to the above, the oil is the correct one for the engine.

I have plugged in my own crappy OBD and here's the code:

 

P0140 $10

O2 sensor circuit No activity Detected Bank 1 Sensor 2. 

methinks Connection or wire? 

Pistonhead
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

P0140 $10 - I don't recognise the high lighted area.  DTC are five digits so given that the P0140 is a valid code.

Any way from what you state " No activity Detected Bank 1 Sensor 2. " there could be a wiring problem to this sensor. Bank 1 is where No:1  cylinder is and sensor 2 is the second in line of the exhaust system in that bank. (I think I am right in thinking No: 1- cylinder is Off - side. Please CHECK don't quote me).

O2 senors come using two different exotic materials; one employing three wires to it and the other employing four wires to it. 

In the four wired version, two wires (usually white cables) are the heater wires in the sensor and the other coloured wires are voltage reference and signal wire to ECU.

Basically, one needs to determine if the voltage from the loom side is registering. An experienced technician should be able to conduct this test easily enough. I will not recite testing procedure as if the wrong wire is probed using an inappropriate tester damage to ECU is inevitable.

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Thanks.

I'll take it to the AMG specialist here, he deals with a lot of exotica and knows their way around a G wagen (if not in Dubai, where?)

My money is on dodgy wiring/connection. 

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

most likely.

 

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Hello,

Recently dealt with a G55 (2009) that had DTCs for both left and right cats. Performance seemed unaffected. Took the O2 sensors out and used a videoscope/borescope (any small camera attached to a wire that fits through the hole) to look inside. Was surprised to find one cat had disintegrated and another was breaking up. Took it to Fox/Skyline exhaust in Al Quoz who replaced the cats at a fraction of the new parts cost, but beware the check engine light will permanently stay on unless you know someone with good Star Diagnostics skills to turn off the cat option.

If you need more info drop me your number by PM and I can explain further on the phone.

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

The Engine ECU will check readings from the sensor after the CAT and compare to those from the sensor before the CAT. it will expect to see a difference, if the CAT is working.

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

M2dxb wrote:

Hello,

Recently dealt with a G55 (2009) that had DTCs for both left and right cats. Performance seemed unaffected. Took the O2 sensors out and used a videoscope/borescope (any small camera attached to a wire that fits through the hole) to look inside. Was surprised to find one cat had disintegrated and another was breaking up. Took it to Fox/Skyline exhaust in Al Quoz who replaced the cats at a fraction of the new parts cost, but beware the check engine light will permanently stay on unless you know someone with good Star Diagnostics skills to turn off the cat option.

If you need more info drop me your number by PM and I can explain further on the phone.

M2dxb wrote:

Hello,

Recently dealt with a G55 (2009) that had DTCs for both left and right cats. Performance seemed unaffected. Took the O2 sensors out and used a videoscope/borescope (any small camera attached to a wire that fits through the hole) to look inside. Was surprised to find one cat had disintegrated and another was breaking up. Took it to Fox/Skyline exhaust in Al Quoz who replaced the cats at a fraction of the new parts cost, but beware the check engine light will permanently stay on unless you know someone with good Star Diagnostics skills to turn off the cat option.

If you need more info drop me your number by PM and I can explain further on the phone.

 

thanks. PM sent. back to Dubai today so I will want to fix this before the car is shipped on the 29th of June. 

As said above, car runs fine. I hate looking at that check engine light mostly. If I have to replace cats, happy to go aftermarket on these. 

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

 

if you want Cats that will not disintegrate, go for metal-matrix types. Not the standard ceramic blocks. The metal versions comparatively have a greater surface area and much less pressure loss.

just as an example: http://stainlessworks.net/catalog/product/view/id/858/?__country=GB

 

 

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Update - the cats were fine, the sensors were fine, it was the wiring which had gone to hell with corrosion at the ECU connection. Apparently common for water to reach this place. 

 

I was wondering how (in Dubai!!!) but then I realised that car cleaners here power wash the engine (never had it done myself obviously!)

I'm picking up the car tomorrow so it should all be ok!

Thanks for the input, really valuable stuff there!

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

I think the ECU is below the dash, under the carpet in the upper part of the passenger foot-well. If too much water from cleaning enters the ventilation scuttle on the engine bulhkead, faster than it normally drains, or its drains are blocked, then it will overflow into the front foot-well area...


Hopefully, will be fixable without a new ECU !

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Spoke too early. Light is back on. 

IF i need a new ECU? Any ideas? At this point I'm considering fixing it in the UK - it ships next week. 

Looking at a reconditioned/second hand part. 

is it  OEM 1131538779?

Any thoughts on costs?

Cheers 

 

 

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

 

The ECU is coded to the vehicle and instrument binnacle for mileage. I don't think you can find a swap that easily, particularly if AMG. If you do, you will need some hack recode.

Best bet may be to send off your original to BBA Reman or similar repair specialist, as the issue, if a corroded circuit track, may be simple to fix with a soldering iron, 

Otherwise, £1,000 or so from dealer.

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Thanks. 

 

I might just do that once the car is on the road in UK. It won't be until September by the looks of it. 

Can't wait to have it in the UK. 

I might want to source some non-specific 18" wheels and winter tyres and  hoping for the worst winter in history :)

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

another minor update, the car is being shipped and I have added full steam clean and undersealing at arrival The underside is in such great nick for the mileage/age that I want to preserve it. 

I have read elsewhere of water leaks into the door/passenger footwell. Not an issue in Dubai, so how would I prevent this? happy to have an indy replace seals and check other stuff if need be, especially considering the electrical problem I already have. 

thoughts? 

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Thought would be - start another thread for this!

Water ingress seems to be the bain of G-Wagens.  Rubber window seals, wiper spindles and blocked drain in the air intake.

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Re Water in Footwells

This was a problem I had but not anymore. Of course it's impossible to say which of the "cures" I undertook was the one that worked but here are some ideas:

1. http://www.gwoa.co.uk/sites/default/files/download_pdf/how_to/Water-Leak...

2. I shouldn't think that your sunroof drains are likely to be blocked given that your G has never seen rain but worth checking the seal that goes around the sunroof in case all that blazing sun might have caused it to suffer.

3. as 2 above. Same goes for the side window scrapers.

4. Check the plastic caps that go over the windscreen wiper spindles in case heat and sun have caused them to crack. Nice cheap replacement item from MB

 

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Stuckmojo wrote:

...I have added full steam clean and undersealing at arrival The underside is in such great nick for the mileage/age that I want to preserve it. ....


To do this properly, you need to remove the plastic wheel-arch-liners to ensure any mud/sand behind them is washed out and then that these hard-to-get-at areas are properly waxed, particularly the inner front wings and the rear corners where there is the  fuel filler pipe to tank.

Don't use tar-based unseal, but a wax-based one, such as DiNitrol 3125:

http://www.rust.co.uk/filestore/DIN%203125%20TDS.pdf

Ensure that the underside of the spring towers and the top shock-absorber mounts are properly waxed, as well as the insides of the tubular chassis cross-members, and the lower bodywork around and behind the rear bumper.

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Update - on the Engine light. The sunroof story will be in the other thread.

Basically, the ECU got waterlogged. MB had the car and it runs 100% fine but the ECU damage means the CEL will always be on. Solution, new ECU. Don't know the cost yet but it will be ££££.

is there a procedure to remove the engine light through STAR? I also just had a new key coded for some £240 so I don't want to have to do that again .

Very annoying as it's only that O2 sensor fault. Or should I just disable the light in the cluster? I am tempted to do this mysef. 

 

Thoughts?

Arnie
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Sorry to hear you still have issues.

All the indications on the dash are communicated through CANbus. You could remove or disconnect or cover the relevant LED on the instrument binnacle to mask the situation. However, if the CEL message is being issued by the ECU, it must believe that there is a fault somewhere, so not sure how MB could pronounce that all is fine? Also, with the ECU being under the passenger-side of the dashboard, I fail to understand how it could have been water damaged unless you have a major issue with your sunroof drains?

A possible solution may be to find a scrap ECU from a similar age, E500 or C500 etc and have your existing PROM (containing the vehicle particulars and engine map) transferred over physically or as firmware contents.

£240 for reprogramming an additional key appears excessive, unless it includes the £200 or so cost of a new key.

You know, you can get a Chinese-clone XENTRY/DAS/STAR  C3 or C4 system (£300 - £500) and do some of the reprogramming and diagnostics yourself, with the same dealer software environment?

 

 

 

 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...
Hi, yes the £240 included the key. Mb want £2200 for the ECU
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

I have been following this thread for a while, in my opinion the yellow engine light is a loose cannon.   On my car Mercedes once changed a sensor in the exhaust system but a few months later the light came on again.  Since then I have ignored it, it is on for a few hundred miles and the goes off for a few hundred miles.  It does not affect fuel consumption and the car has passed the MOT each time (but then the light was off during the MOT test).

I own more than one car from different manufacturers. In my experience, identifying electric/ electronic issues via the local dealerships is a lottery.  I tend to follow the following route:  if the issue seems to be not urgent, I wait until the next service, have the issue diagnosed and priced.  If I regard the analysis as credible I have it repaired. If I have my doubts I wait until the next service, usually they have a different diagnosis at the next service.

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Hi

I can see you want things right

You have tried everything and i understand it is frustrating

If it runs fine and is perfect just use it and stop worrying. Yes i would feel like you and want it right but you are wasting so much time and money in life

I draw a line and say enough is enough

Run it and if anything goes wrong it might be the issue everyone was missing

Drive it and enjoy it. Stick some tape on clocks so you dont keep seeing the light

Not what you want to hear but if mercedes and everyone else can not find an issue just drive the thing

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

I agree, actually.

I'm having a go at switching the light off on the panel via STAR/Developer with my mechanic on Monday. 

This is the procedure. 

[img]https://ibb.co/na9uCn[/img]
[url=https://ibb.co/na9uCn][img]https://preview.ibb.co/k2YMsn/Capture.jpg[/img][/url]

 


http://[url=https://ibb.co/na9uCn][img]https://preview.ibb.co/k2YMsn/Capture.jpg[/img][/url]

 

Final question, how do I find the part number for my ECU, engine is the M113K

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Now, I May have found a couple of companies who can repair the ECU, but I need the part number. Hopefully my indie will provide before I have to dismantle the car. 

Also, small rattle when cold from power steering. Possiblty fluid is low.

 

What's the spec for the oil? Cheers. 

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Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Thanks Arnie, I ordered it. 

I'm still looking for a part number for the ECU. I might as well dismantle the glove box and have a look myself. When it stops raining in about 7 months...

I begrudge paying £2,200 for a new ECU if I don't need one.

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Replying to myself. A couple of companies either swap the ECU and recode for about £900 and one claim to be able to fix it. 

 

I guess I need to access the ECU and take it out. 

Do I need to disconnect battery and I guess remove the glove box? How hard a job is this? DYI or do I need my specialist to do this? 

Turnaround for these is quite quick so i'll go ahead. 

 

Cheers

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

I knew I'd read about this somewhere - it's an old article so maybe they're not still around or if they are maybe they don't offer the same "lifetime guarantee". Anyway, hope it's of some interest:-

https://www.honestjohn.co.uk/news/parts-and-accessories/2011-10/bba-reman/

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Hi, thanks, I did contact them and they won't touch that particular unit. However I found others who will give me a refurbished ECU to then marry to my car (expensive but 40% of the MB cost). 

I'm cross checking the ECU at the weekend and if numbers match I'll go for it. 

 

 

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Further minor update. A company in Plymouth seems to be able to repair the ECU, though they want a photo of the label to cross check part number. 

How hard a job is it to take the glove box out, look for sticker (1)

then, how do I remove the ECU? Do I disconnect the battery and just unplug? 

Thanks in advance. 

BTW if this works cost is less than £200 versus £2200 from dealer...

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

buddy take the battery off first.

Anything electric take lead off battery

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

1. Take battrery lead off And then Take the small screw off the black plug on ECU like a small Star type.

2. Push black square block to one side Left way - its like a clamp for the connectors to ECU.

3. Before removing the two bolts on the sides to remove completly...... get electrical cleaner in spray can and do both sides ie: male and female connections leave for 10-15 mins plug back in and have a drive around see if that works before replacing/re-coding ECU.

4. If that fails then speak to the chaps in Plymouth.

cheers

Gooch

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

gooch wrote:

1. Take battrery lead off And then Take the small screw off the black plug on ECU like a small Star type.

2. Push black square block to one side Left way - its like a clamp for the connectors to ECU.

3. Before removing the two bolts on the sides to remove completly...... get electrical cleaner in spray can and do both sides ie: male and female connections leave for 10-15 mins plug back in and have a drive around see if that works before replacing/re-coding ECU.

4. If that fails then speak to the chaps in Plymouth.

cheers

Gooch

 

Thanks Gooch, I had a look (need a new battery anyway).

1  - I took the glove box off - easy, 4 screws and one light connector

2 - I took the bottom box off - 3 screws and the plug for the power socket. 

3 - I'm stumped. The ECU sits in a tray next to a fuse box. I can't work out how it's secured in the tray - the black plastic bit. I haven't moved it now as it seems that the ECU will need repairing but so need the plugs. ECU will go to Plymouth but I now need someone who can take on the plugs job - re-pinning them (my Indie won't touch it). Local Merc agreed to take out the ECU and fix the "car" end for me - waiting for a quote - then they will put the ECU back in once returned and that SHOULD be it.  

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Hi mate,

Tray, it should slide out one way, ?

You'll get there soon keep us all updated

Need anything else let me know.

Cheers

Gooch

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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Another minor update. Battery failed (it was in warranty so I put a new one in), cleared all faults with my little OBD reader and will take the car to a car electrician near me on Tuesday to look at the plugs/ecu. He'll check what needs to be done. 

The plan is:

- Check condition of the plugs (local specialist), agree on re-pinning of plugs. My indie says it's very complex but to me it just looks like wires into plugs. Not rocket science but way beyond my comfort zone. Surely that's what a car electrician does 

- Take ECU out (either he does it or I do it) and send for repair. Car sits without ECU. 

-  3 days later receive fixed ECU, plug in with new plugs and that should solve the issue once and for all. 

Worst case scenario, buy reconditioned part or scrap part and have data transferred over from damaged ECU. I found someone who can do that for £40 

Edit - I agree that it should just slide out (down, probably). Dubai garage seemed to be able to take it out without removing the dash. Anyways, I'll keep this updated. 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Another update. 

ECU has been taken out and it's with an ECU repair company. Fingers crossed they can replicate the fault and fix it. There is minor corrosion on some of the pins. 

The plugs car-side look ok but in case the ECU is found fault free, I'll have an electrician replug them (he has the car now). 

Best case scenario - ECU is fixed, plugged in, problem solved

Worst case scenario - ECU needs replacing, that's £799 + VAT including recoding. 

Fingers crossed I might have it sorted by the end of this week. 

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Final update - hopefully. ECU reconditioned, cabling tidied up and the damned light is gone. Happy me. 

jdring
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...

Quite a saga.  Darn electronics can be a pain.  Hope you have miles/years of error free ECU.

Stuckmojo
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Re: G55K - Check Engine Light - O2 sensors - all replaced, ...
Thanks. Now I have a sunroof to fix :)