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My daughter has recently acquired a 2007 Suzuki SX4 1.6 petrol with 140,000 miles. The eml light has come on and plugging in an OBD reader has returned a P0420 error "catalyst system efficiency below threshold bank 1". Monitoring the O2 sensors output in TorquePro shows a waveform for sensor 1 and a 'flat line' response for sensor 2. Given that the car passed an MOT very recently and presumably passed the emissions test is it resonable to assume that the 02 sensor has failed.
As its within the 30 day warranty, the dealer is offering to replace the O2 sensor but my concern is whether the Catalytic Convertor may be faulty.
Appreciate anyones thoughts and advice.
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Unlikely to be a lambda sensor fault.I would suspect a faulty catalyst.However, this very often does not fail an emission test with this fault code.
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This is my concern, obviously the o2 sensor is the cheaper option and this is why the dealer wants to replace this.
I've been checking the emissions results from the last mot compared to previous ones and the HC reading on the last MOT was 90ppm, up from <20ppm on the previous tests.
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Is the downstream one showing low or high? High presumably indicating rich, otherwise the EML wouldn't be on....
If the cat was failed, and the upstream one was swinging rich to lean, then I would expect the downstream one to be doing the same. If it is flatlining high, then I reckon the lambda sensor is a good bet. An IR thermometer can be used to see if the CAT is working as there should be a temp rise across it.
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Is the downstream one showing low or high? High presumably indicating rich, otherwise the EML wouldn't be on....
If the cat was failed, and the upstream one was swinging rich to lean, then I would expect the downstream one to be doing the same. If it is flatlining high, then I reckon the lambda sensor is a good bet. An IR thermometer can be used to see if the CAT is working as there should be a temp rise across it.
The downstream sensor is showing high - however, the plot thickens. I've been to my local suzuki dealer and they agree it's very likely to be the CAT, "a very common problem" I was told as soon as I told them what the error code was. BUT, according to them there's only one o2 sensor despite Torque displaying data for Sensor 1 and Sensor 2 ??
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I would say that 99% of petrol engine cars built after year 2000 will have at least 2 sensors.Take a look here,but again,I don't think that is your problem. www.ebay.co.uk/itm/Fits-Suzuki-SX4-EY-GY-1-6-Genui...6
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Update: it appears that the SX4 does have two o2 sensors
upstream/sensor 1: 18213-80JB0
downstream/sensor 2: 18213-63J12
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I have a 2007 SX4 1.6 with this problem. i have had it for a long time and reset the code on a fairly regular basis. It is a software fault in the management software and a Suzuki dealer should have the code to correct the issue. I do have the Suzuki reference somewhere and I'll try and dig it out for you. My SX4 has done 185000, a lot of it with this 0420 issue. I don't worry about it at all, I just clear the light and carry on. It does seem like a nice way for dealers to sell a cat converter and other parts. Cynic or realist? I will try and find the software update reference.
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Reference my previous post the Suzuki Bulletin ref is BE:Q:G:031. A dealer should be able to access this and apply the software update.
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Thanks for the reply. I'm not convinced that there is a TSB for this.
I've spoken to my local Suzuki dealer and they have no knowlege of this TSB
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There used to be a SX4 user site at suzuki4u.co.uk, but this has recently closed down. I got the Bulletin reference from a poster on that site who said they applied the fix to all their regular customers when in for routine services, so I assumed he worked for a Suzuki garage. As I said previously I never bothered to follow up as I have a basic OBD tool and I can reset the light in a couple of minutes. I use a local mechanic for my servicing (after the Suzuki garage suggested I needed a new cat), and he sees a few of his other Suzuki customers with the 0420 issue too. My SX4 has no trouble with the MOT emission tests so 0420 no problem for me.Incidently I can make the light come on through a certain driving routine! Good luck with your problem. T.
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The catalyst needs carbon monoxide and oxygen to enable the chemical reaction to take place. That is why the engine runs rich and lean, rather than at the ideal all the time. Not having a good understanding of chemistry, the catalyst reorganises the atoms so that the harmful gasses are converted to non harmful.
A P0420 code is set when the pre and post O2 sensor readings are too similar, indicating that the catalyst is not doing it's job efficiently. You will most likely end up replacing it. It's very good practice to replace the O2 sensors along with it.
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Railroad, thanks for that, this supports my hypothesis that the boolean logic in the engine management software accepts "equal to" as a fail. This matches my driving pattern test for 0420 activation. We are probably staring to drift off the original thread now, but final question, why do you need a new O2 sensor and, or cat if the vehicle passes the emission tests?
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There is a TSB that mentions P0420 - TS 04 11307 - "ENGINE OIL FILTER CHANGE PRECAUTIONS; O2 SENSOR CONTAMINATION POSSIBLE CAUSE OF DTCS P0137 AND/OR P0420" affects SX4 MY2007 only
This just points out that the location of the 02 sensor is prone to drips from the oil filter and that the oil can stop the sensor working correctly. Later models had the o2 sensor relocated to prevent the problem from happening.
I will try and get under the car tomorrow to see if there is any sign of oil on the sensor.
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but final question, why do you need a new O2 sensor and, or cat if the vehicle passes the emission tests?
Because the O2 sensor compares the difference between the oxygen present in the exhaust to that outside, which makes up 21% of the atmosphere. A rich mixture consumes more oxygen than a lean one and so the difference is greater. This can be seen as a high voltage. A low voltage means little difference and is shown when the mixture is lean. The O2 sensor cannot measure CO, and so the ECM cannot know how much carbon monoxide is present. The catalyst works by chemical reaction and is not controlled by the ECM.
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Railroad, thanks for your detailed technical reply. Just interested to know how I would have benefited over the past four plus years I have had the intermittent 0420 issue if I had replaced the cat converter/02 sensor as suggested by the Suzuki dealer. My SX4 has done lots of miles in that time and passed the emission test each time. Do you think there is more that one issue causing the 0420 warning to appear?
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I would use your scantool to do some live data checks. Pay particular attention to the fuel trim figures. Do some Google research on Short Term and Long Term Fuel Trim.
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