P0422 / P0432 intermitant faults

[ex4x4]

Hi folks - thought id share my concerns and hopefully glean some infomation regarding my CEL light.
My latest MB to join the paddock is a C230 2006 - non Komp. it has the V6 2.5 engine.
shortly after buying it the CEL came on. I checked it with my Autel scanner - which showed a P0432 and P0422 fault.
The fault is saying basically the down stream O2 sensor is giving a below threshold reading for both branches of exaust.
these two fault codes are the same - just for different banks of the V engine exhaust system.
Now for info - the engine runs sweet as a nut, no smoke, no hesitation, pulls like a train and MPG appear normal - 29mpg combined.
Ther two cats do not rattle when banged with heel of hand.
the O2 sensor wiring appears undamaged.

the fault code will clear and not return until a certain part of a repeated journey. IE I can drive around town and lower speed roads all day without fault. The fault appears when driving at motorway speeds and cruising.
I have checked through and vac tested Vacuum hoses. Evap solenoid not passing. secondary air system functioning and solenoids,diaphragm units operatiing.
Im finding it hard to believe that both cats would fail at same time and then only throw a fault at high speed cruising with an engine running at normal operating temps.

Ive measured O2 output voltages on sensors with my Autel unit - down stream sensor voltages do vary from 0.8v to 0.1v every few seconds and cat inlet /output temps differ by 60-70'c

As a test I have fitted a shroud / fooler to one of the banks O2 sensor and it reads 0.1v constantly - but still throws a fault for both banks.

spark plugs appear and normal greyish white - but have not been replaced. Air filter and oil filter have been replaced and a good dose of redex through system.

What else can I check before buying new cats.

 

[PobodY]

Any chance it's that the lambda sensors have had it? Maybe a previous owner was a bit liberal with fuel additives that they don't like.

 

[ex4x4]

Any chance it's that the lambda sensors have had it? Maybe a previous owner was a bit liberal with fuel additives that they don't like.

A possibility - but I think the sensors throw their own code when they breakdown??

 

[Old spanners]

I had a similar problem on my C180 and the after cat O2 sensor heater circuit was open circuit. Measured the resistance with a multi meter across the two white wires (may be different with others but generally two the same colour out of the 4) with the plug disconnected don't put any voltage across the others.

 

[ex4x4]

I had a similar problem on my C180 and the after cat O2 sensor heater circuit was open circuit. Measured the resistance with a multi meter across the two white wires (may be different with others but generally two the same colour out of the 4) with the plug disconnected don't put any voltage across the others.

I'll give that good looking at - and report back my findings.

 

[ex4x4]

Well measured resistance of sensor heating elements - @19ohms. I had a "other new" sensor kicking about workshop which measured 10ohms. - not a great difference.
I have spliced in one of these new senosrs to bank 1 and left bank 2 untouched.
the same fault occurred 10 miles down motorway. Hoping the fault would only be for the untouched bank - but no - both banks faulting with below threshold.
looking like an exspensive trip to MB specialist for new cats???

 

[Larkone]

Had a similar issue with resistance on a Lexus - bad O2 sensor, bought an aftermarket equivalent and car ran fine but code came straight back. Turned out that Lexus are sensitive about the resistance, cant remember the exact values but the aftermarket one was not exactly the same - something like the difference between 7 Ohms and 12 Ohms. So fitted a Bosch that had the right resistance and all was good - no more codes.

May help

 

[Old spanners]

That's ok for the heater circuits a little difference is no problem as it shows the circuit is working. Another thing to check would be the plug on the ECU for any corrosion, oil or dirt as this is where the signal for both banks ends up.
BTW how many miles are on the engine.

 

[ex4x4]

107,000 miles

 

[ex4x4]

Hi all - just an update ( albeit long winded) regarding my P0422,32 faults, on my 2006 c230 w203 with M272
This fault generally includes post cat O2 sensors but fault still remained after swapping them out the fault still occurred.
Against common sense - I then swapped out the pre cat O2 sensors (with Bosch, but not oem) - thinking they had been in for 100k and maybe becoming a bit lazy in reaction to fuel /air trims triggering the afore mentions codes.
( on a side note - you CAN solder these joints without the world ending, although you do need a high power iron to get solder to "wet" the conductors)
SUCCESS - although short lived.
The codes have dissappeared - only to be replaced with the annoying P0410 secondary air system fault.
I have since systematically worked through and proved out every component of ths system ,but fault ever present.
works completed.......
Air motor - was working although noisey. removed /stripped/cleaned with electrical contact cleaner. bearing degreased and repacked with grease. Rebuilt and refitted - now blows like a tornado.

All vacuum lines tested and holding over 20"hg.

Vacuum control valve - removed, flushed through with contact cleaner and tested - holds vaccum.

Vacuum operated diapragm/check valves - diapragm side checked for leaks - ok. Valve stem lifts around 5"Hg and fully opened at 10"Hg.
valve seat cleaned with carb cleaner. check valve enclosure/reeds were coked up. stripped components ( drilled out reed reatining bolts) and decoked parts. rebuilt. reeds close on reverse ( exhaust side) flow and open on intake ( air pump side )flow.
NB found reeds to be naturally semi open - not sure if they should be normally closed??? but left them in their discovered state.
Whilst diaphragm valves were removed - the manifold ports were tested for free flow with air line - found to be open and clear.

during operation a vaccuum gauge has been attatched to vaccuum in line from vac' control sol' valve to diaphragm valve to see what sort of vaccuum is being generated and for how long. when air pump sequence is initiated - the system pulls over 20" Hg - so Im sure diaphragm valves are fully opening.

I have ran car with Torque app running and monitored O2 sensors during cycle. Now being a wide band 5 wire O2 sensor - I'm unable to measure output in mv but can monitor Lambda equivalent ration both commanded and actual. during cycle the commanded ratio is 2.0 and actual is 1.2.. Thinking this was down to air pump delivery dropping off - I have tried blowing an airline into air pump intake hose at same time in the hope the extra air will increase O2 actual reading but to no avail.


Other possible relevant info - long term fuel trim values around 7% bank 1 and 4 % bank 2 - although short + long trim never above 10% and generally short term in negative %. Maf sensor changed to try to change these figures to no effect. - possible samm amount of umetered air but not a great concern.

So pretty stumped now - not entirely sure what is causing error code.
Any help would be greatly appreciated.