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Discussion Starter #1
P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Can anybody help with finding out what could be causing this other than broken Cats.

The Bank1 & Bank 2 codes came on simultaneously so I think twin failure is unlikely.

I have a 2002 L322 V8 Vogue with BRC LPG Conversion.

PCV hoses have been replaced a few weeks ago.
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

OK, I've done some more research on this. This code is thrown when there is not enough difference between the Pre-Cat and Post-Cat sensors, ie it takes a measurement of the gasses before they enter the Cat, and then after to make sure the Cat is doing it's job.

If you get this error it means the Post-Cat sensor thinks too much O2 is getting past the Cat, this can be caused by a cracked manifold, a leaking manifold joint or the like.

But it can also happen if you do lots of short trips and the cat never gets up to temperature properly, the recommendation is there is a Secondary Air Injection Pump that is supposed to superheat the cat, maybe this is having issues?

Berb from the manual on the SAI pump:

The secondary air injection system is used to limit the emission of carbon monoxide (CO) and hydrocarbons (HC) that
are prevalent in the exhaust during cold starting of a spark ignition engine. The concentration of hydrocarbons
experienced during cold starting at low temperatures are particularly high until the engine and catalytic converter
reach normal operating temperature. The lower the cold start temperature, the greater the prevalence of
hydrocarbons emitted from the engine.

The SAI pump is used to provide a supply of air into the exhaust ports in the cylinder head, onto the back of the
exhaust valves, during the cold start period. The hot unburnt fuel particles leaving the combustion chamber mix with
the air injected into the exhaust ports and immediately combust. This subsequent combustion of the unburnt and
partially burnt CO and HC particles help to reduce the emission of these pollutants from the exhaust system. The
additional heat generated in the exhaust manifold also provides rapid heating of the exhaust system catalytic
converters. The additional oxygen which is delivered to the catalytic converters also generate an exothermic reaction
which causes the catalytic converters to 'light off' quickly.

The catalytic converters only start to provide effective treatment of emission pollutants when they reach an operating
temperature of approximately 25?C and need to be between temperatures of 40?C and 80?C
for optimum efficiency. Consequently, the heat produced by the secondary air injection “after burning”,
reduces the time delay before the catalysts reach an efficient operating temperature.
The engine control module (ECM) checks the engine coolant temperature when the engine is started, and if it is above
-9º C but below 50?C, the SAI pump is started. Secondary air injection will remain operational for a period controlled
by the ECM. The SAI pump operation can be cut short due to excessive engine speed or load.

Just some thoughts, I'm not massively clued up on how the emmisions system works on the L322, it's v advanced.

Dan
 

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Discussion Starter #3
Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Dan_UK_1984 said:
OK, I've done some more research on this. This code is thrown when there is not enough difference between the Pre-Cat and Post-Cat sensors, ie it takes a measurement of the gasses before they enter the Cat, and then after to make sure the Cat is doing it's job.

If you get this error it means the Post-Cat sensor thinks too much O2 is getting past the Cat, this can be caused by a cracked manifold, a leaking manifold joint or the like.

But it can also happen if you do lots of short trips and the cat never gets up to temperature properly, the recommendation is there is a Secondary Air Injection Pump that is supposed to superheat the cat, maybe this is having issues?

Berb from the manual on the SAI pump:

The secondary air injection system is used to limit the emission of carbon monoxide (CO) and hydrocarbons (HC) that
are prevalent in the exhaust during cold starting of a spark ignition engine. The concentration of hydrocarbons
experienced during cold starting at low temperatures are particularly high until the engine and catalytic converter
reach normal operating temperature. The lower the cold start temperature, the greater the prevalence of
hydrocarbons emitted from the engine.

The SAI pump is used to provide a supply of air into the exhaust ports in the cylinder head, onto the back of the
exhaust valves, during the cold start period. The hot unburnt fuel particles leaving the combustion chamber mix with
the air injected into the exhaust ports and immediately combust. This subsequent combustion of the unburnt and
partially burnt CO and HC particles help to reduce the emission of these pollutants from the exhaust system. The
additional heat generated in the exhaust manifold also provides rapid heating of the exhaust system catalytic
converters. The additional oxygen which is delivered to the catalytic converters also generate an exothermic reaction
which causes the catalytic converters to 'light off' quickly.

The catalytic converters only start to provide effective treatment of emission pollutants when they reach an operating
temperature of approximately 25?C and need to be between temperatures of 40?C and 80?C
for optimum efficiency. Consequently, the heat produced by the secondary air injection “after burning”,
reduces the time delay before the catalysts reach an efficient operating temperature.
The engine control module (ECM) checks the engine coolant temperature when the engine is started, and if it is above
-9º C but below 50?C, the SAI pump is started. Secondary air injection will remain operational for a period controlled
by the ECM. The SAI pump operation can be cut short due to excessive engine speed or load.

Just some thoughts, I'm not massively clued up on how the emmisions system works on the L322, it's v advanced.

Dan
That's very interesting and may well be a factor.

The Local LR garage put he car up on a ramp this morning and had a look at the Cats. They are welded in and they think they are after market as they are not the normal size for a L322 (too small!)

They can detect no manifold or exhaust leaks.

Therefore they think replacing the Cats with the correct size and/or LR OEM equipment will clear the fault.

Geeeeeze that could be £800+ :crybaby2:

PS: Does anybody know where to get the correct size & functioning Cats and a good price?
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Gazellio said:
PS: Does anybody know where to get the correct size & functioning Cats and a good price?
Try These people

Have you had this problem from day 1? if they are the wrong size then I would have thought you would have noticed quickly...

By the way - were they refering to the Pre-Cat (5) or the Main-Cat (6)? Maybe they got confused and thought the Pre-Cat was it and the Main-Cat was a silencer box?

[attachment=0:37prdoh4]Exhaust.JPG[/attachment:37prdoh4]
 

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Discussion Starter #5
Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Dan_UK_1984 said:
Gazellio said:
PS: Does anybody know where to get the correct size & functioning Cats and a good price?
Try These people

Have you had this problem from day 1? if they are the wrong size then I would have thought you would have noticed quickly...

By the way - were they refering to the Pre-Cat (5) or the Main-Cat (6)? Maybe they got confused and thought the Pre-Cat was it and the Main-Cat was a silencer box?

[attachment=0:26zpaek4]Exhaust.JPG[/attachment:26zpaek4]
Thanks,

The problem is linked with the previous Lambda fault that cleared after replacing the PCV hoses. The new fault then appeared after about 4 days. It could be that the new fault was hidden by the previous one due to the effect on the exhaust gases.

The Land Rover garage must know about Range Rover Cats in detail so I assume they know which is which.

Having seen underneath it looks like replacement Cats have been welded in so its my guess they were cheap after market replacements. However these "replacement" Cats may have been fitted by previous owner due to the same fault code as I am getting and failed to cure it!

Very frustrating and I cannot find fault codes in the RAVE CD?
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Dan_UK_1984 said:
This code is thrown when there is not enough difference between the Pre-Cat and Post-Cat sensors, ie it takes a measurement of the gasses before they enter the Cat, and then after to make sure the Cat is doing it's job.
Exactly, and the downstream sensor is telling the management system that the cat isn't working properly.

Do you run the car on LPG most of the time - i.e. more than 90% of the time? Have you thought that the LPG system isn't in the correct trim, or can't correct the trim for some reason? Can you get it somewhere where the upstream and downstream sensors can be scoped by a PicoScope or similar?
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

I have given an opinion of this fault on another forum,but no mention was made of aftermarket undersize cats.Dont assume that the LR garage will fully understand your car - they often dont and will just change parts to try to get rid of fault codes.I still maintain that you need to get all 4 oxy sensors scoped - with the engine running on petrol,and emissions test it at the same time.With how accurate and clever the Motronic injection system is the cats should not have to do much final treatment on the exhaust gases.Basically the codes you are getting are caused when the downstream sensors follow too closely the waveform of the upstream ones - which under most closed loop conditions will be switching once a second or more.The downstream ones should drift around,going rich or lean only on overrun or wide throttle openings/heavy loads.
The emissions test on petrol will quickly tell if the cats are up to it,at the 2500-3000rpm test the Co should be .20 % - or VERY close to zero and the Hc's be less than 10ppm. If this is the case then the cats are working well and the engine is running closed loop.
If that is not the case and the downstream sensors are switching in time with the upstream ones then you do need cats.A good emissions test means that my original thoughts about the LPG not being trimmed properly are correct.If the LPG cannot respond quickly enough to trim fuelling,(Usually too lean.)under heavy loading then the upstream oxy sensors will just hover and fail to switch up rich.The engine ecu will not get the right response from the oxy sensors and keep trying - till it logs codes and defaults to open loop.When the upstream sensors hover like this the downstream ones can easily follow - so the ecu thinks the cats are failing to treat.Up comes your code.
You need a better garage with more knowledge who will understand,test and measure.And its not an hours work to do it,so should cost less than £50 - at an independant.
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

allyv8 said:
I have given an opinion of this fault on another forum,but no mention was made of aftermarket undersize cats.Dont assume that the LR garage will fully understand your car - they often dont and will just change parts to try to get rid of fault codes.I still maintain that you need to get all 4 oxy sensors scoped - with the engine running on petrol,and emissions test it at the same time.With how accurate and clever the Motronic injection system is the cats should not have to do much final treatment on the exhaust gases.Basically the codes you are getting are caused when the downstream sensors follow too closely the waveform of the upstream ones - which under most closed loop conditions will be switching once a second or more.The downstream ones should drift around,going rich or lean only on overrun or wide throttle openings/heavy loads.
The emissions test on petrol will quickly tell if the cats are up to it,at the 2500-3000rpm test the Co should be .20 % - or VERY close to zero and the Hc's be less than 10ppm. If this is the case then the cats are working well and the engine is running closed loop.
If that is not the case and the downstream sensors are switching in time with the upstream ones then you do need cats.A good emissions test means that my original thoughts about the LPG not being trimmed properly are correct.If the LPG cannot respond quickly enough to trim fuelling,(Usually too lean.)under heavy loading then the upstream oxy sensors will just hover and fail to switch up rich.The engine ecu will not get the right response from the oxy sensors and keep trying - till it logs codes and defaults to open loop.When the upstream sensors hover like this the downstream ones can easily follow - so the ecu thinks the cats are failing to treat.Up comes your code.
You need a better garage with more knowledge who will understand,test and measure.And its not an hours work to do it,so should cost less than £50 - at an independant.
This is a really excellent and well thought through reply and I thank you for taking the time to set out my options so clearly. I will be taking your suggestions to an independent tomorrow to get the emissions tests done on Petrol to see if the Cats are working.
Can you explain how you Scope the Oxy (Lambda) sensors correctly?

Finally I am not sure if you are aware that after "Clearing" the faults the car runs for about 3-4 days (75 miles plus) perfectly under all load conditions before the light eventually comes back on. I have noticed that the light comes on at various different times and not necessarily under heavy load or overrun - could be when I start the engine or even at tick over at the lights etc. I tried the same test using Petrol only and the light came back on after the same 3-4 days.....

Does the above change your thoughts in any way?
 

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Discussion Starter #9
Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Rich998a said:
Dan_UK_1984 said:
This code is thrown when there is not enough difference between the Pre-Cat and Post-Cat sensors, ie it takes a measurement of the gasses before they enter the Cat, and then after to make sure the Cat is doing it's job.
Exactly, and the downstream sensor is telling the management system that the cat isn't working properly.

Do you run the car on LPG most of the time - i.e. more than 90% of the time? Have you thought that the LPG system isn't in the correct trim, or can't correct the trim for some reason? Can you get it somewhere where the upstream and downstream sensors can be scoped by a PicoScope or similar?
Light comes on after 3 days plus driving whether on LPG or Petrol. Whats a PicoScope?

Many thanks.
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

It is a worry that the Mil comes back on with petrol use too,but even that could be a result of the long term trims being too far out as the petrol ecu has tried to adapt to the characteristics of the LPG system.The Picoscope that Rich mentions is the ideal tool to scope your Oxy sensors,it is a PC based oscilliscope set up for automotive use - it is really a top bit of kit and is fast becoming the industry standard.Rich has a posh 4 channel usb version,mine is an older 2 channel one using the serial port.
The sensors need scoping via the black wire from each sensor,the upstream ones should be switching in a fairly smooth loop form 0 - 0.8v and back down in around a second or less.This should happen at idle and at any steady load /speed condition.Floor the throttle and they should stay up rich at 0.8v,on overrun they should stay down lean.The downstreams should sort of hover around 0.4-6v whilst the upstreams are switching and the cats are hot,(Ie,during the fast idle part of the emissions test) but not at idle as the cats wont stay hot enough to work.
If you have got undersize aftermarket cats that dont work then you have a problem,the originals will be very expensive - but many aftermarket ones are very poorly made or simply dont work at all.(Had this recently with a 1.8 Freelander.) But you really need to test all this as I described or you could end up with a large bill and still have the lamp on.
If you do end up needing cats,I would even consider secondhand ones from a breaker if they will give a short warranty with them,in my experience the original ones always work better than the aftermarket ones.If nothing nasty is done to a good quality cat they will last alot longer than is claimed for them,but it does rely one the engine running properly in the first place.When it is all setup properly and the Mil stays off,even if the problem was not the LPG I still strongly advise you to get the LPG ECU trimmed to accurately mimick the petrol trims.
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

allyv8 said:
It is a worry that the Mil comes back on with petrol use too,but even that could be a result of the long term trims being too far out as the petrol ecu has tried to adapt to the characteristics of the LPG system.The Picoscope that Rich mentions is the ideal tool to scope your Oxy sensors,it is a PC based oscilliscope set up for automotive use - it is really a top bit of kit and is fast becoming the industry standard.Rich has a posh 4 channel usb version,mine is an older 2 channel one using the serial port.
The sensors need scoping via the black wire from each sensor,the upstream ones should be switching in a fairly smooth loop form 0 - 0.8v and back down in around a second or less.This should happen at idle and at any steady load /speed condition.Floor the throttle and they should stay up rich at 0.8v,on overrun they should stay down lean.The downstreams should sort of hover around 0.4-6v whilst the upstreams are switching and the cats are hot,(Ie,during the fast idle part of the emissions test) but not at idle as the cats wont stay hot enough to work.
If you have got undersize aftermarket cats that dont work then you have a problem,the originals will be very expensive - but many aftermarket ones are very poorly made or simply dont work at all.(Had this recently with a 1.8 Freelander.) But you really need to test all this as I described or you could end up with a large bill and still have the lamp on.
If you do end up needing cats,I would even consider secondhand ones from a breaker if they will give a short warranty with them,in my experience the original ones always work better than the aftermarket ones.If nothing nasty is done to a good quality cat they will last alot longer than is claimed for them,but it does rely one the engine running properly in the first place.When it is all setup properly and the Mil stays off,even if the problem was not the LPG I still strongly advise you to get the LPG ECU trimmed to accurately mimick the petrol trims.
Brilliant thanks again.

I still strongly advise you to get the LPG ECU trimmed to accurately mimick the petrol trims.
Is it likely that only a LPG converter/specialist could this properly?
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Yes,you do need an LPG specialist to trim your Gas system,sorry but I dont know anyone in the SE area to recommend.It might be worth searching on an LPG forum for a good recommendation.Alot of places pay little attention to tuning as it can be time consuming,which is why there are so many complaints about it.As for the cat suppliers,well - I really cant say,trouble is most exhaust places are selling boxes of kippers and yet again wouldnt know what was wrong if a car failed an emissions test.I guess if the cats pass the lastest E103 ? regs then they should be OK. Also a good guide is the actual size of the monolith or brick of the cat,the Freelander one I mentioned earlier was only about a 1/3 the size of the original brick - it had no effect on the gases at all,I measured the gases with and without the cat in the system......
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

allyv8 said:
The sensors need scoping via the black wire from each sensor,the upstream ones should be switching in a fairly smooth loop form 0 - 0.8v and back down in around a second or less.This should happen at idle and at any steady load /speed condition.Floor the throttle and they should stay up rich at 0.8v,on overrun they should stay down lean.The downstreams should sort of hover around 0.4-6v whilst the upstreams are switching and the cats are hot,(Ie,during the fast idle part of the emissions test) but not at idle as the cats wont stay hot enough to work.
Many of the USB OBDII graph O2 sensor data, would you consider that sufficient to base a diagnostics on? I'm interested to know because i've always seen the graph but never really known what i'm looking at, but your description above makes it make sense now!

 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Dan_UK_1984 said:
allyv8 said:
The sensors need scoping via the black wire from each sensor,the upstream ones should be switching in a fairly smooth loop form 0 - 0.8v and back down in around a second or less.This should happen at idle and at any steady load /speed condition.Floor the throttle and they should stay up rich at 0.8v,on overrun they should stay down lean.The downstreams should sort of hover around 0.4-6v whilst the upstreams are switching and the cats are hot,(Ie,during the fast idle part of the emissions test) but not at idle as the cats wont stay hot enough to work.
Many of the USB OBDII graph O2 sensor data, would you consider that sufficient to base a diagnostics on? I'm interested to know because i've always seen the graph but never really known what i'm looking at, but your description above makes it make sense now!

Dan, Do you have a screen shot graph of the pre & post Cat Oxy Sensor readings? (Should have my Scope soon!)

Gary
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Gazellio said:
Dan, Do you have a screen shot graph of the pre & post Cat Oxy Sensor readings? (Should have my Scope soon!)

Gary
I dont have a graph of that to hand, but if you check out Bank One - Sesnor One - Sensor Two and Bank Two - Sensor One - Sensor Two

The data is there and is captured, I just haven't got a graph of it, and its too dark and cold outside to get you a fresh one!

[attachment=0:3w05kwlh]Main Page - Start up.jpg[/attachment:3w05kwlh]
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Dan_UK_1984 said:
Gazellio said:
Dan, Do you have a screen shot graph of the pre & post Cat Oxy Sensor readings? (Should have my Scope soon!)

Gary
I dont have a graph of that to hand, but if you check out Bank One - Sesnor One - Sensor Two and Bank Two - Sensor One - Sensor Two

The data is there and is captured, I just haven't got a graph of it, and its too dark and cold outside to get you a fresh one!

[attachment=0:m2qeqb46]Main Page - Start up.jpg[/attachment:m2qeqb46]
Thanks mate what software is that?
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Digimoto

See PM :wink:
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

Dan_UK_1984 said:
Digimoto

See PM :wink:
OK the car has been in my local Land Rover garage for testing.

RESULTS:

TEST 1.
Fast Idle Test

Oil Temp. 70 (pass)
Speed: 2450-3050
CO 0.3 (pass)
HC 200 (pass)
Lambda 0.95 - 1.09 (pass)

Idle Speed Test

Speed: 450-1050
CO 0.5 (pass)

Exhaust Emmissions Test (Pass)

TEST 2.
Fast Idle Test

Oil Temp. 77
Speed: not checked
CO 0.30
HC 7ppm
Lambda 1.00

Idle Speed Test

Speed: not checked
CO 0.37

Exhaust Emmissions Test (Pass)

SUMMARY

Fast Idle Test: PASS

Oil Temp. 70 (pass)
Speed: 2450-3050
CO 0.3 (pass)
HC 200 (pass)
Lambda 0.95 - 1.09 (pass)

Idle Speed Test: PASS

Speed: 450-1050
CO 0.5 (pass)

OVERALL RESULT: PASSED

Does this mean anything to you guys and how does it effect your thinking re the Cats?

Another thing s that the test mechanic thought the car was a supercharged as its real quick and the LR garage said it was so much faster than standard that it must have been chipped! However they also said chipped and LPG can cause ECU problems.....
 

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Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)

That kinda says the cats are working as they should.

But seriously the garage thought it was supercharged!? The things going through their mind should have been: Age of the vehicle = too old for SC, BMW engine = Not SC, after looking at the engine = it's not SC. Was this a LR Dealer or an indy? Either way I would never go back! Were these the same people who told you the cats were too small?

D
 
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