Difficulty separating cable from coolant sensor.

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I am finding it extremely difficult to pull this Yaris (2002) cable connector from the coolant sensor as I can only just get one hand in. Is it just a question of tugging as hard as possible or do the two red-arrowed prongs need to be squeezed simultaneously? Thanks, kindly for any help.

Coolant sensor connectio.jpg
 
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Wow, another great victory, John, thanks again. ;) I got it off with a bit of prying (not the voyeur kind, thank you :mrgreen:).

Now my next question. I am trying to determine whether I require a replacement coolant sensor as I have found the engine fan appears to be on all of the time. From the TEMPERATURE/RESISTANCE table (see below) that I am using a cold engine (say 12°c) should provide a resistance of 3.03 Kohms. Well the sensor is providing that exactly and I am inclined to think that there may be nothing wrong with it at all. But do I need to run the car to get the engine warm and confirm that susequent readings comply with the table before I can properly eliminate the sensor from the problem cause?

You may remember I raised this problem a couple of months or so ago but rather stupidly thought that another connection was that of the coolant sensor. What is additionally rather confusing is that the fan seems to have 3 different speeds and also comes on when the air-conditioning is deployed. Mr Haynes (R.I.P.) provides some decent info in the manual but sadly neglects to include an electrical diagram which covers the fan or indeed the air-con.

Resistance to temperature graph with cold annotation.png
 
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Fan will come on with the Aircon active.

Really you need to see what the PCM thinks the temperature is (diagnostics).
 
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Is it just me, or are electrical connectors on modern vehicles deliberately difficult? Every time I work on my Scudo van and need to disconnect an electrical connector, they all seem different. Some need small screwdriver to lever small plastic locking tab, some have a piece of wire in them that needs to be squeeezed, some you squeeze the two tabs, etc, etc. No two connectors seem to have the same release mechanism/method. However, the most annoying thing is that they're often installed with the bit that needs to be levered/squeezed to release on the underside of connector so you can't see it and have to do it by feel (thinking in particular of the connector to air mass sensor on my Scudo's air filter box that needs disconnecting to remove filter box).

Suppose if you're working on them all the time it's no problem, but it can take a bit of head scratching sometimes.

Apologies for rant/hijack! ;)
 
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Well the car at tickover today read ECT 87°c which I guess is fine. Is there anything that should give cause for concern in the collection readings below? I was in the car alone so unable to check take a measure of these values at 1,500 and 2,500 rpm as is usually recommended.

Snapshot of code readings 11th May at tickover.png

R&C: Agreed, the Toyota electrical connectors appear to cover several different styles but are all conclusively a PITA to disconnect. I guess this makes for a more dependable connection which, presumably, is what matters most. Unlike yourself I have not discovered any inverted connectors but there is always time.
 

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Your long term fuel trim is very high at +23.4% normally they top out at 25%.

On a perfect engine it would be 0%, normally up to 10% is acceptable.

Basically your car is adding 23% extra fuel over stock based on the O2 sensor (lambda) readings.
 
Thanks, Keith, I see what you mean. If there actually is an issue of over-fuelling then any fault certainly betrays no detectable odour and the car is currently garaged. But about 10 days ago I did a journey of around 150 miles and about midway I noticed the MIL had come on – this only ever happened previously last year when the catalyst was seized by some opportunists, though, seemingly resolved following fitting of the (non-Toyota) cat & lamda sensor* replacement.

I then tried to investigate further with the OBD2 code-reader. This is a pretty new item for me and with my ‘investigation’ I found that there was a fault code of P1035. Unintentionally, I must have managed to erase the code from the vehicle. Of course I am aware that this will hardly remedy the problem and it now is apparent that there is a more pressing issue to resolve than just the fan running constantly. Maybe, as you say, should the long term fuel trim rise to 25 then the MIL will illuminate again? Meanwhile are there any recommended checks to make given the ‘clues’? I will take a shuftie of the MAP sensor and look for any leaks etc.

* I have heard that when replacing a lamda sensor the OEM type (Denso) should be used. This was not the case but the replacement item would appear to have worked perfectly well for many months.
 
When the trim tops out it will activate the MIL.

There could be a number of causes really, air leaks, the O2 sensor is not correct for the calibration of the PCM, dirty injectors etc.

Ideally you'd have a calibrated wideband in the downpipe before the CAT, if this reads 14.7:1afr while car is in closed loop then that proves your aftermarket O2 sensor is ok and the PCM is reading correct exhaust mixture.

If the Wideband reads richer it shows your aftermarket O2 sensor is not working properly or not correct for the PCM's internal calibration.

Would be interesting to compare your injector opening time at idle against another Yaris.
 
The codereader is a relatively basic Foxwell NT301 and I am not sure that it shows the AFR, though, I may be wrong here. As it happens I have access to another Yaris though it is a couple of years newer and is a 1.3. Presumably worth a test to make a comparison?
 
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