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.

 

M2dxb
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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 :)