Is the problem reported by these trouble codes serious?
Super Member
Joined: Oct 2023
Posts: 538
Likes: 190
W221 S500
A sensor throwing a code is the result of one of two things...
1. It is functioning correctly and something is amiss.
Or...
2. The sensor itself is the fault and it's reporting incorrectly.
The only way to determine which with a degree of certainty is to watch the live data and see if the information being reported is consistent with the same sensor on the opposite bank. If it's not and there are no other symptoms/indications then it's a faulty sensor. If any other parameters are amiss upstream of the sensor then the sensor is functioning correctly and there's another issue.
The fuel cleaner serves to clean the injectors as a partially clogged, sticky or failing injector(s) is the only reason why the fueling, and therefore, cat efficiency might be affected on one bank but not the other. Ok, that's not entirely accurate, a clogged air filter could also do it when there's one for each bank, likewise a failing spark plug or coil. But no evidence to suggest a misfire in this case.
People always jump to faulty sensor without considering the possibility that the sensor is actually working correctly.
Live data before and after the fuel system clean will provide a reasonable comparison for further investigate if it's required.
The fault code itself serves as a starting point for a proper invesigative diagnostic process, it is not THE diagnosis.
1. It is functioning correctly and something is amiss.
Or...
2. The sensor itself is the fault and it's reporting incorrectly.
The only way to determine which with a degree of certainty is to watch the live data and see if the information being reported is consistent with the same sensor on the opposite bank. If it's not and there are no other symptoms/indications then it's a faulty sensor. If any other parameters are amiss upstream of the sensor then the sensor is functioning correctly and there's another issue.
The fuel cleaner serves to clean the injectors as a partially clogged, sticky or failing injector(s) is the only reason why the fueling, and therefore, cat efficiency might be affected on one bank but not the other. Ok, that's not entirely accurate, a clogged air filter could also do it when there's one for each bank, likewise a failing spark plug or coil. But no evidence to suggest a misfire in this case.
People always jump to faulty sensor without considering the possibility that the sensor is actually working correctly.
Live data before and after the fuel system clean will provide a reasonable comparison for further investigate if it's required.
The fault code itself serves as a starting point for a proper invesigative diagnostic process, it is not THE diagnosis.
If the sensor behaviour is consistent one side to the other, your issue lies elsewhere.
If they're wildly out, then that is an indication of a problem that requires further investigation. It may be a faulty sensor, but equally it may not be.
Replacing the sensors just because the internet says so would be a fools errand. You could spend $$$ and not solve anything.
Super Member
Joined: Oct 2023
Posts: 538
Likes: 190
W221 S500
Ask yourself this:
Why is one bank reporting overfueling? I suspect that one or more injectors is sticking or partially clogged.
If you want to swap parts, swap the injectors from.Bamk 1 over to Bank 2 and vice versa. If the fault at the Cats swaps sides, you've proved that the fault is indeed an injector. If the fault doesn't move then it's a sensor.
The fact that running fuel cleaner through the system has improved the issue for a period of time should be a clear indication that you're on the right track with the cleaning.
Senior Member
Joined: Mar 2018
Posts: 492
Likes: 182
2006 W221 S500L M273
MBWorld Fanatic!
Joined: Aug 2014
Posts: 5,315
Likes: 1,672
S500
The fuel cleaner serves to clean the injectors as a partially clogged, sticky or failing injector(s) is the only reason why the fueling, and therefore, cat efficiency might be affected on one bank but not the other. Ok, that's not entirely accurate, a clogged air filter could also do it when there's one for each bank, likewise a failing spark plug or coil. But no evidence to suggest a misfire in this case.
.
fuel delivery issues could be many
fuel pressure
faulty injector wiring
a broken injector
tumble flaps snapped off
valve issue,
and so on
its highly likely the CAT is close to worn out - in today’s world they are super fragile junk (we are way past the old 1980s - early 90s Merc ones where so robust they totally blocked and stopping the engine running). Today, 5 mins driving with an ignition fault (popped coil stick) and the CAT overheats and either efficiency falls off a cliff or it burns through and does almost nothing...
my 2006 5.5ltr V8 is a Euro 4 emission std car - running a grown up system with an AFR sensor measuring the actual air fuel ratio before the CAT and a old world budget 02 sensor Post CAT - it very normal for heater circuits to fail on Bosch O2 sensors at 10-12 years (the heater allows the sensors to respond more quickly)
like wise it almost guaranteed 4 or more coils will have failed during its lifetime before its reached 70k miles as they are utter junk - leading to a nasty over fuelling situation and CAT overheating drive that will have not done the CATS any good
Super Member
Joined: Oct 2023
Posts: 538
Likes: 190
W221 S500
of course its not really measuring fuelling - the engine management system is measuring sensor data against a set of values determined by the manufacturer, once outside their limits the light comes on
fuel delivery issues could be many
fuel pressure
faulty injector wiring
a broken injector
tumble flaps snapped off
valve issue,
and so on
its highly likely the CAT is close to worn out - in today’s world they are super fragile junk (we are way past the old 1980s - early 90s Merc ones where so robust they totally blocked and stopping the engine running). Today, 5 mins driving with an ignition fault (popped coil stick) and the CAT overheats and either efficiency falls off a cliff or it burns through and does almost nothing...
my 2006 5.5ltr V8 is a Euro 4 emission std car - running a grown up system with an AFR sensor measuring the actual air fuel ratio before the CAT and a old world budget 02 sensor Post CAT - it very normal for heater circuits to fail on Bosch O2 sensors at 10-12 years (the heater allows the sensors to respond more quickly)
like wise it almost guaranteed 4 or more coils will have failed during its lifetime before its reached 70k miles as they are utter junk - leading to a nasty over fuelling situation and CAT overheating drive that will have not done the CATS any good
fuel delivery issues could be many
fuel pressure
faulty injector wiring
a broken injector
tumble flaps snapped off
valve issue,
and so on
its highly likely the CAT is close to worn out - in today’s world they are super fragile junk (we are way past the old 1980s - early 90s Merc ones where so robust they totally blocked and stopping the engine running). Today, 5 mins driving with an ignition fault (popped coil stick) and the CAT overheats and either efficiency falls off a cliff or it burns through and does almost nothing...
my 2006 5.5ltr V8 is a Euro 4 emission std car - running a grown up system with an AFR sensor measuring the actual air fuel ratio before the CAT and a old world budget 02 sensor Post CAT - it very normal for heater circuits to fail on Bosch O2 sensors at 10-12 years (the heater allows the sensors to respond more quickly)
like wise it almost guaranteed 4 or more coils will have failed during its lifetime before its reached 70k miles as they are utter junk - leading to a nasty over fuelling situation and CAT overheating drive that will have not done the CATS any good
And whilst what you're saying re today's sensors etc is justified, these cars are getting on for 20 years old, there's no Chinesium in them. Having things fail at that age is not unreasonable be it sensors or suspension bushes. The Omega for example, regardless of engine would suffer from 8-10 predictable failures during the 80-120k mile window. Do serious miles and things people get surprised by such as suspension bushes become regular service items.
The W221 is unlikely to be any different. That said my '07 ML has just passed its MoT with an advisory for front pads and nothing else... That has 205k miles and still has it's original suspension. So some cars do seem to last better than others.
Don't know about you, but I would rather drive a 20 year old Mercedes with all its quirks and features than a new **** box. The only possible exception to this, is it I were to start driving for Uber in which case a new Camry would be hard to beat. But my daily would still be an older Mercedes.
