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Discussion Starter · #1 ·
Iv got a corsa c 1.2 2006 sxi, it failed mot last week on emissions long story short I changed backbox from spotted to standard new o2 sensor and new cat, since then I'm only getting 17mpg when before the garage I was getting 26mpg and also when car is cold driving along at a steady speed its jumpy and stumbling until its up to temp, how can a new cat and standard everything else make mpg go down so much any help will be appreciated. Thanks
 

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First thing i would do is a code test, second thing i would do is leave the battery disconnect for 1/2 hours or longer...3rd thing i would do is look at the Lambda sensor wiring, make sure you haven't got the plugs round the wrong way or on the wrong sensors...it could be temperature sender unit..if its a Corsa you can do a pedal test for codes...oh i would check the air filter and put some injector treatment in the fuel tank....good luck from Fred in Essex.
 

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Discussion Starter · #3 · (Edited)
Iv had the lambda changed twice in the last 4month as diagnostics kept coming up with a fault on o2 sensor but engine light is still on, plus the flappy door where I put the fuel in is broke off so its just stuck in place at the moment but it's got the fuel cap on properly, thanks for the advise on disconnecting the battery will try that in the morning and check the plug for the sensors could it be oil or fuel filter or does it sound more like a serious problem. Thanks
 

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Hi well i dont like the sound of fitting Lambda sensors, apart from the fact they cost a lot...i assume you fitted the front one, as that controls the mixture, the back one does very little, its tells you how well the cat works, but either can put the light on, you can tell me what the code number is and i will tell you exactly what it means, you can do a code test with the pedals with that...there are tests you can do on the sensors depends how technical you are with multimeters...Fred.
 

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Hi Martin well lets see from my list...

P0130 02 Sensor Circuit Malfunction (Bank I Sensor 1)
P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0170 Fuel Trim Malfunction (Bank 1)

So ok the fuel trim is saying its rich or lean, you can forget about that one for time being, P0130 says the front Lambda sensor if faulty
P0141 says that the heating circuit is up the creek on the same sensor, so lets think about this, everything really is pointing to the front sensor, you only have 1 bank so dont worry about that,,,concentrate on the front Lambda sensor the rear one after the cat seems ok.....

OK so are you any good with a multimeter or circuit tester, what you really need to do if you dont have an OpCom device is this, there are 4 wires on the sensor, 2 white which are for the heating element, and a black which is the signal wire to the ECU and a Grey which is the earth for the sensor relative to the black one...

So what i would do is this, put a multimeter or a bulb type circuit tester on the two white wires with the engine running if possible when the engine is cold, and you should get 12 volts across them, if not check fuse and wiring etc...also if you think the sensor is faulty take the plug out, put an ohm meter across the two white wires and it should read about 5 ohms, that is the heating element part, now we move on to the sender unit that controls the mixture, if you put you multimeter on the lowest voltage setting, and put the leads across the back and grey wires, with the engine hot you may have to let it idle or rev it etc...the voltmeter should fluctuate between 0 and 1 volt, typically you will see 200- 800 millivolts, or 0.2 to 0.8 volts same thing.....if it does that it working....

Have you disconnected the battery for half hour, try to get rid of all the codes see if they come back, if you want to test the sensor itself, take it out, put in a vice put voltmeter on low volts, put leads across black and grey, when sensor is cold it will read zero volts, when it is red hot it will read up to 1 volt, you would have to heat it up with a blowlamp....if it does that its ok, and while its out check resistance across white wires again, 5 ohms or so....if you done all that your half way there good luck from Fred in Essex.

Just pulled some codes off it p0130-o2 sensor heater relay malfunction, p0141-1/2 o2 sensor relay, p0130 again???, p0170-fuel trim bank 1
 

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Discussion Starter · #7 ·
Im no good at any of that multimeter stuff but will try get hold of one and go should the steps youv mentioned. Would the o2 sensor really make my mpg go from 26 to 17 in such a short time though? Been reading up about the fuel trim malfunction and from what iv read its could be anything from a list of about 10things from maf sensor to vaccym leak on air intake to exhaust leak, just been on the phone to the garage that did the repairs and changed the front sensor told them none of these codes was on and mpg was fine u til they had it and that I want it sorting they said to take it in and they will replace the sensor for free and check the exhaust fittings where they changed the cat free of charge I said I should think so haha
 

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Well Martin the easiest way to cure it is take it to a garage and let them do it, but not sure how much it would cost...yes a naft oxygen sensor can dramatically effect you MPG, if its not supplying any current at all to the ecu it indicates a weak mixture, and the ecu responds buy dumping a ton of fuel into the engine....its like driving an old style car about all day with choke pulled right out,,,it will run as rich as hec, i bet the plugs are black if you take them out, and it doesn't do the catalytic converter a lot of good either...yes there are several things that effect the fuel trim, the fuel trim basically is the mixture, if you can get the mixture right as it should be the fuel trim will automatically come down to where it should be, i assume its around 20+ on the short term at the moment..that indicates a lean mixture and the ecu is trying to compensate, when it doesn't really need to, but its getting its info from the Lambda sensor and that is faulty your up the creek a bit....if you can do the test i suggested it will tell you what the lambda sensor is really doing....it could be a faulty ECU.....the codes are generated from that....Fred.
 
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