Emissions Failure - Testing Lambda Oxygen Sensors?

[The Cherrys]

Hi, my Gen 7 190 has just failed it's MOT on emissions. I don't use Mr T, just my local garage so I need to try and pin down where the problem lies - could be the sensors or maybe the cat, it has done 127000 miles.

Has anyone tried testing their Celica sensors (before and after cat) in situ, with their multimeter?

Report from the MOT place is:

Exhaust emissions carbon monoxide content at idle excessive

Exhaust emissions carbon monoxide content after fast idle excessive

Exhaust emissions hydrcarbon content after 2nd fast idle excessive

Exhaust emissions Lambda reading after 2nd fast idle outside specified limits

(I need to get the exact readings off them)

I see you check the fluctuating voltage, but anyone know which wires, etc?

Thanks,

Peter

[PhilGee]

How does it drive? I failed one a week ago (not t-sport, just vvti) and it turned out to be the airflow sensor causing the problem. The sensors inside get fouled up and cause a lack of power and no fault codes. Cleaned it up with brake cleaner and it cured the problem. Normally if you've got a prob with the oxy sensors i will flag up a fault code. But not always.

[The Cherrys]

It drives well, though mine is a bit of a hybrid as it is LPG converted too, so it doesn't do much on petrol. The airflow sensor I've actually cleaned (instructions off here), when I first had it a couple of months ago, I can't say it was dirty though, but I did it anyway.

I have not changed the plugs since I've had it admittedly, but I took a look at one of them and they seemed OK and the gaps were within limits - they apparently last a good 50K miles. Air filter has been changed. It runs pretty well, LPG or petrol, no much difference between the two really.

There are no lights on the dash & as I've said, I've not had any diagnostic equipment put on it at all, as only my local garage has MOT'd it & I service it myself.

Anymore thoughts?

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How does it drive? I failed one a week ago (not t-sport, just vvti) and it turned out to be the airflow sensor causing the problem. The sensors inside get fouled up and cause a lack of power and no fault codes. Cleaned it up with brake cleaner and it cured the problem. Normally if you've got a prob with the oxy sensors i will flag up a fault code. But not always.

[martin1810]

It drives well, though mine is a bit of a hybrid as it is LPG converted too, so it doesn't do much on petrol. The airflow sensor I've actually cleaned (instructions off here), when I first had it a couple of months ago, I can't say it was dirty though, but I did it anyway.

I have not changed the plugs since I've had it admittedly, but I took a look at one of them and they seemed OK and the gaps were within limits - they apparently last a good 50K miles. Air filter has been changed. It runs pretty well, LPG or petrol, no much difference between the two really.

There are no lights on the dash & as I've said, I've not had any diagnostic equipment put on it at all, as only my local garage has MOT'd it & I service it myself.

Anymore thoughts?

---------------------

How does it drive? I failed one a week ago (not t-sport, just vvti) and it turned out to be the airflow sensor causing the problem. The sensors inside get fouled up and cause a lack of power and no fault codes. Cleaned it up with brake cleaner and it cured the problem. Normally if you've got a prob with the oxy sensors i will flag up a fault code. But not always.

A lambda fault will usually put the engine management light on and will register a dt code. You need to get a code read to find out if anything is logged. I wonder if the air flow sensor is actually working.

[PhilGee]

Spark plugs normally get changed 6yrs or 60k miles. Special plugs aswell. Not had much to do with LPG but am guessing all that is ok. Is your set-up a 2 sensor system? Think the plugs for the sensors are tucked behind the carpet in the drivers footwell where it goes up behind the centre console. Should be 2 plugs with 4 wires in them. Cant remember exact colours but normally blue, black and white. As for testing them i'm not 100% sure on which ones to probe to get the voltage reading. Supposed to use an osciloscope to get accurate readings. In my experience its normally the heater circuit in the sensors that fail but like i say this normally brings on the engine warning lamp and gives a fault code.

[The Cherrys]

Thanks folks - can most garages attach and get the codes off or is it just Toyota that can do this?

Is there any way of testing if the air flow sensor is working OK?

It should be a 2 sensor system I think - not looked underneath yet to check. But from what other posts say, it should be.

I've looked at the justlambda website & taken a couple of extracts & put it below, the wire colours depend on whether the car has universal or Toyota sensors on it. As its been serviced at Mr T until now, then they should be Toyota ones. They reckon the 2 black wires are heater, blue signal, white earth. They give the testing procedure below, so I'll give it a try tomorrow. Interestingly they don't reckon they work until 300 degree's C, so it makes me wonder if the garage let the car warm up OK - or does the MOT test equip make sure the engine is up to temp ?

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The sensor can be tested for output by connecting to it a digital voltmeter, set to a 2v scale. Connect the +ve test lead to the sensor signal wire [see wire colours] and the -ve test lead to earth/battery -ve. The voltage produced should swing from app 0.2v to 0.8v and back around once per second. If the voltage is stuck high then the engine is probably running rich for some other reason. If stuck low then usually either a faulty Lambda Sensor, air leak or an engine running very weak for some reason.

[martin1810]

Thanks folks - can most garages attach and get the codes off or is it just Toyota that can do this?

Is there any way of testing if the air flow sensor is working OK?

It should be a 2 sensor system I think - not looked underneath yet to check. But from what other posts say, it should be.

I've looked at the justlambda website & taken a couple of extracts & put it below, the wire colours depend on whether the car has universal or Toyota sensors on it. As its been serviced at Mr T until now, then they should be Toyota ones. They reckon the 2 black wires are heater, blue signal, white earth. They give the testing procedure below, so I'll give it a try tomorrow. Interestingly they don't reckon they work until 300 degree's C, so it makes me wonder if the garage let the car warm up OK - or does the MOT test equip make sure the engine is up to temp ?

-------------------

The sensor can be tested for output by connecting to it a digital voltmeter, set to a 2v scale. Connect the +ve test lead to the sensor signal wire [see wire colours] and the -ve test lead to earth/battery -ve. The voltage produced should swing from app 0.2v to 0.8v and back around once per second. If the voltage is stuck high then the engine is probably running rich for some other reason. If stuck low then usually either a faulty Lambda Sensor, air leak or an engine running very weak for some reason.

I think it's about 0.4 - 0.55v on this car. It will be interesting to see if your multimeter can manage to show this as it cycles. Yes the garage will have got it hot and yes most garages can read emissions related dtc's. It seems odd that the lambda sensors could be faulty and no MIL on.

[The Cherrys]

I'll take a look tomorrow. The option is the cat, any idea's on testing if that has gone or not ??

Thanks for your help, I'll try and put the results here tomorrow. Peter

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I think it's about 0.4 - 0.55v on this car. It will be interesting to see if your multimeter can manage to show this as it cycles. Yes the garage will have got it hot and yes most garages can read emissions related dtc's. It seems odd that the lambda sensors could be faulty and no MIL on.

[The Cherrys]

OK, firstly cleaned the sensors this morning, both very clean anyway. I put the tester on, I had to put a pin down the end of the connector to get a reading. Interestingly it held steady at about 0.9V, this was whilst the car was running on LPG, I switched it to petrol & then it started to vary. Difficult to get an accurate reading on a digi meter, it varied somewhere between 0.18 and 0.9, sometimes 0.3, 0.4, etc. But it did move. Tested the other sensor, exactly the same thing happened.

I'm wondering whether they knock out the lambda's when on LPG? Any thoughts, I'll scan the web to see.

[martin1810]

OK, firstly cleaned the sensors this morning, both very clean anyway. I put the tester on, I had to put a pin down the end of the connector to get a reading. Interestingly it held steady at about 0.9V, this was whilst the car was running on LPG, I switched it to petrol & then it started to vary. Difficult to get an accurate reading on a digi meter, it varied somewhere between 0.18 and 0.9, sometimes 0.3, 0.4, etc. But it did move. Tested the other sensor, exactly the same thing happened.

I'm wondering whether they knock out the lambda's when on LPG? Any thoughts, I'll scan the web to see.

The readings that you have got don't tell you anything about your problem apart from suggesting that the sensors are working. You need an actual oscilloscope read to tell you what the signal actually is. If you look in the gen7 manual it shows you some likely patterns. I can't believe you don't have the MIL on. Does this light when you turn on ignition and then go out when it starts. You really need a code read.

[sjrainsford]

When did you actually fail your emissions test mate, running on gas or petrol?

[The Cherrys]

That's what I thought regarding the sensors, I'm interested about the MIL though. This does not come on when I turn on the ignition from start ... does this definitely come on before you start the engine ??

Found a page on http://www.toyotacelicaonline.com/error.htm regarding reading service lights. This is for Gen 6, does this work for Gen 7 too?

Ta, Peter

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Check your Battery voltage (should be greater than 11 volts), turn off all accessories, put your car in neutral, and make sure your car is at operating temperature.

Jump the terminals TE1 and E1of the "Data Link Connector 1" with a jumper wire (a paperclip will do).

Turn the ignition to "On" (but dont start the car)

Read the trouble code by watching the flashes of the check engine light

Sample Trouble Codes: These codes are for a 6th Gen. Celica...They may, however, be similar and/or carry over to other cars.

Code Blink Circuit

n/a 8 flashes normal

12 1, then 2 G, NE signal (#1)

13 1, then 3 G, NE signal (#2)

14

1, then 4 Ignition Signal Circuit

16 1, then 5 A/T Control Signal

21 2, then 1 Oxygen Sensor Signal

22 2, then 2 Engine coolent Temp Sensor Signal

24 2, then 4 Intake Air Temperature Sensor

25 2, then 5 Air/Fuel Ratio Lean Malfunction

26 2, then 6 Air/Fuel Ratio Rich Malfunction

27 2, then 7 Sub-Oxygen Sensor signal

31 3, then 1 MAP sensor

41 4, then 1 Throttle Position Sensor signal

42 4, then 2 Speed Sensor Signal

43 4, then 3 Starter Signal

51 5, then 1 Switch condition signal

52 5, then 2 Knock Sensor

71 7, then 1 EGR System

The readings that you have got don't tell you anything about your problem apart from suggesting that the sensors are working. You need an actual oscilloscope read to tell you what the signal actually is. If you look in the gen7 manual it shows you some likely patterns. I can't believe you don't have the MIL on. Does this light when you turn on ignition and then go out when it starts. You really need a code read.

[The Cherrys]

Anyone know about the MIL ?

Took the car to an LPG specialist today, put the car on the tester. Hydrocarbons way out on LPG, but everything passes on petrol. They hadn't got the right connector to change the LPG settings, so for now I took the car back to the MOT station and forced it onto petrol - straight through!

Getting somebody else to look at the LPG next week, apparently my system does not link up to the Lambda's, hence why they were not working on LPG. This is apparently correct though. Once they get this right then I should get a few more MPG's out of my gas.