Hi there my retired neighbour has a 2004 1.8 petrol mondeo with a fault code of P0546 exhaust temp sensor bank 1 sensor 1, just rang local ford dealer and not much help. I have changed a few lamba sensors before on my toyota and would like to save him a hefty bill by changing his sensor, could someone please advise which sensor it is pointing to and best place to get one from please. Am I right in thinking there are two lamba sensors one either side of the cat and this temp sensor is underneath the car further along ? Any help would be really appreciated please.

Thank you.

If it's identified as Lambda sensor you can loot at places like http://justlambda.com - they supply the identical bosch part in lot of cases but lot cheaper than from a Ford dealer.

If you've not got one already a decent lambda socket or wrench saves a lot of agro too. 22mm on my ST, but can't say if Mondeo will be same size.

Thanks but the fault code says exhaust temp high, not oxygen sensor so that's why I'm confused a bit, I was hoping the ford dealer would be as helpfull as toyota dealers but not, couldn't tell me anything apart from they think there may be four sensors on that car, just don't want him getting ripped off, I can change it but need to know which one it is. Tried searching and someone has suggested it has two wires and not four like the O2 sensors but not sure if this is correct . Thanks for reply.

Thanks but the fault code says exhaust temp high, not oxygen sensor...

Yes, but if the lambda sensor is shot to the point that the engine is running weak (and I've no real evidence that this is the case, just floating the possibility), then the exhaust temperature will go high, and you will see this fault, eventually. Does the fault come on immediately after start-up (which would suggest wiring, etc) or does it take, say, half an hour to get there?

Presumably, no one has stuck an exhaust gas analyser up its exhaust to see what that says?

I was hoping the ford dealer would be as helpfull as toyota dealers but not, couldn't tell me anything apart from they think there may be four sensors on that car,

Getting help (as in helpful help) from a Ford Dealer is an extended topic all on its own. Usually, if you can talk to an actual mechanic, if you get the right one, can be helpful but usually they'd rather you talked to someone who doesn't know. Ho, hum.

...they think there may be four sensors on that car, just don't want him getting ripped off, I can change it but need to know which one it is. Tried searching and someone has suggested it has two wires and not four like the O2 sensors but not sure if this is correct . Thanks for reply.

There will be quite a lot of sensors; wasn't sure if you were referring to just Lambda sensors, engine sensors or even more generally.

Anyway, heated Lambda sensors will have three or four wires. Sometimes, particularly on older cars, the ones next to the cylinder head aren't heated, because they warm up pretty quickly, anyway.

Temperature sensors will be one or two wire - one wire uses the body to connect to metalwork of the engine for the 'earth' connection (four wire temperature sensors are also possible, but I don't know of them being used in this application).

On a car of this age, I would expect a sensor upstream of the cat and one downstream; the upstream may be close to the cylinder head, rather than the cat itself, for reasons to do with keeping the sensor warm (they need to be warm to work). Again, some cars will have 'per cylinder' sensors, but I doubt that this is one of them.

If you have proper diagnostic tools, you would be able to get voltage readings (waveforms) out of pre- and post- cat sensors, and that would give you a clue. assuming that you don't, and aren't prepared to get them, it would probably be best if you went to some independent who did (or find a friendlier Ford place, which could be an interesting diversion).

Thanks for help, he has just had a knee replacement op so car had sat there for 2-3 months not used and was ok before that, Now started to use again with this fault coming up, have cleared the fault code twice hoping it would stay reset after car has been used again but not. Car runs fine no problems other than engine man light comes on. Not sure when it comes back on will have to ask him, i know once i clear code and restart car it dosen't come on, so must be after a little while of driving.

What I'm thinking of doing is removing each sensor and test with a meter if can work out what I should be looking for on my meter ! Some will no doubt have 4 wires and some 3 & 2 so scratch head time I reckon but might be best way forward to find which one I require and then source one.

Been struggling to obtain a new sensor as out of stock everywhere but have read on talkford that someone wired in a 2.2k ohm resistor and done away with it completely, has anybody tried this if so did it work and not damage the ecu ?