Our fiestas engine light has been on for a while so we decided to buy a diagnostic kit (cost so much to go to a garage and it happens quite often so cheaper to buy one) and it comes up saying "generic catalyst effieciency below threshold (bank 1)"

any ideas what could be wrong with it? Its a 1.25 zetec btw.

Thanks

Never encountered that one but first thing to do would be tap into the Lambda sensor and see if the voltage is jumping up and down rapidly (what the trade loosely call "switching" --- if it is the engine is runing closed loop which is good.

Also give the catalyst(s) a bump with your hand to check if it rattles inside the catalyst matrix could broken up.

If your diagnostic interface can capture live data check the coolant tempetutre sensor (CTS) and other sensors are giving sensible readings.

[Edited on 25/6/08 by britishtrident]

interesting page

http://www.eurocats.co.uk/technical.php

ye will try that thanks,

just wondering why it mentions bank 1? any ideas?

Bank 1 is just the first bank of cylinders -- ECU harware is standardised so the sensor channels and fault codes also have to cover V engines, on an inline engine the ECU thinks Bank 2 exists but null readings are normal..

think you find the cat is knackered,has it had a missfire in the past from a faulty coil?.You can delete the fault code (dtc) but it will come back.If you remove the cat,which is a pain on a fiesta you will prob find its rattling around in there.

From http://www.obd-codes.com/p0420


P0420 OBD-II Trouble Code
Technical Description

Catalyst System Efficiency Below Threshold (Bank 1)
What does that mean?

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms

You will likely not notice any drivability problems, although there may be symptoms.
Causes

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions

Some suggested steps for troubleshooting a P0420 code include:

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.