Evening all,


This car has MOT emission problems and presented codes relating to fuel trim and lambda sensor fault. PO125 also appeared (insufficient coolant temperature for closed loop fuel control). I have scanned the CTS at 98c, coolant fan cuts in and I have measured the voltage at the sensor at 0.48v. This sensor appears to be ok. The other fault codes have been cleared and do not come back. PO125 clears and then comes back after 10-15mins. Now here is my query. Lambda sensor sometimes works and sometimes not. When all is well the emissions are perfect. I think the lambda sensor and CTS are OK but there is a soft-ware problem with the ECU. Your thoughts would be appreciated.

Regards

Pete M

Hi Pete,
What were the other codes ? TPS/02/MAF by any chance !

Regards
Dave

Hi Dave

PO130 - O2 sensor circuit malfuction (Bank
1sensor 1)

PO170 - Fuel Trim malfunction (Bank 1)

Everything on this vehicle checks out ok and no problems with driveability. CO is high at approx 3% and HC and CO2 reflect this (natural and fast idle). When O2 sensor switches,everything is at it should be. PO125 is affecting it and there must be a correlation between that and O2 sensor.

Regards

Pete m

Hi.

When you say O2 sensor stops switching does it react to the high CO reading (I.E: does it show steady at around 0.9v) or does it stick at another, lower voltage? When it stops switching does it react to introducing lots of air by blipping the throttle? The sensor does not need any input from the ECU to start working. If it stops sending any kind of signal or reacting in any way then it is likely to be U/S.

HTH - Paul.

Hi Paul,

O2 sensor sits at approx 0.1v for an age on a hot engine with CO at approx 3% with no re-action to any input from me to stir it into action. Pico-scope will then see it burst into life albeit the trace is a bit crappy and all emission readings come good. Sensor is about 1 year old and made in Italy (No make present). Normally, I would have no hesitation in changing it BUT, cost is £133 plus VAT and have nagging feeling that PO125 is playing a part in this.

Regards

Pete M

Hi pete,

First of all, being an Autologic user, how on earth do you cope using the likes of ACR and ACT2 on other manufacturers vehicles with their ltd functionality? I would have thought you would have had at least a dedicated asian tool like multiscan or Carmanscan?

Back to the point in question, I have had a similar code deffinition on a Toyota Yaris (PO125 insufficient coolant temperature for closed loop fuel control), but this had a very slow warm up of engine coolant due to a faulty thermostat. I advised new thermostat but customer brought car back claiming it was the same as before.. in fact it was not the same as before because the engine was now warming up correctly but it was still flagging the same code. After further investigation I noticed the lambda sensor was not generating a proper output (too low). Fitting a new lambda sensor cured this one, I suspect you may have to do the same.

HTH

Mike

HMMMMMMM I think I may have got you confused with another Pete, If so.....sorry for the confusion.......DOH!!!

Evening all,

Done more research on PO125. This can be flagged up by a normal cooling system fault which is easily diagnosed. However......IF the ECU fails to see that the Lambda Sensor is switching after 140secs for approx 2 mins, then the ECU can be fooled into thinking that the engine is too cold and then flags up the fault. So, with this in mind, and with this Lambda sensor doing precisely b....r all for minutes at a time I have taken the plunge and will fit a new one tomorrow.

Regards

Pete M

PS

Michael. Its not what you got but how you use It!. I have no problem with my gear for diagnostics and very rarely do I get stuck for an accurate diagnosis. Dunno who this other Pete is!

Evening all,

Stuck the new sensor on and cleared the codes and bingo all is well. Lady now has a new MOT Certificate and EML remains off. So PO125 was caused by a faulty HO2 sensor which confused things a bit.

Many thanks for all your inputs and advice.

Regards

Pete M

Thank you very much. I'll be here all week. Don't forget to tip your waitress!