Strange 172 problem

[mikeherts]

Dont know if anyone has any ideas or has had this themselves?

Today I was just coming to the end of an hour long motorway run in my 172. As I saw the turn off I wanted, I indicated over and noticed that my temperature guage had dropped down to cold. It then shot back up and down (like a boost guage on a turbo).

I was on the overrun decelerating for the junction - when I got down to the speed I wanted to keep in the slow lane, I put my foot back on the accelerator but the car started to limp. Felt very rough, and hardly accelerated - spluttered a bit. Pulled off the motorway and up to the traffic lights up the slip road. I hald expected (dreaded!) it to stall, but it didnt. Instead it ticked over at about 2-2500rpm. I pulled away and it was very down on power and hesistating all the time - really really rough.

It seemed to snap out of it a few minutes later and was ok on the way home later on. Though my temperature guage started doing its boost guage/oil pressure guage impersonation all the way again.

It had plenty of fuel (had filled up before setting off), no it wasnt diesel and no it wasnt sub-standard fuel. Neither the STOP or SERV lights came on at any time. I just cant think what it would be

Anyone had this? Thanks in advance for any advice!

 

[BenR]

Check the connections on the coolant temp sensor, or it could be a faulty sensor itself.

 

[JAY172]

sounds like the coolant temp sensor had a fault(most likely open circuit somewhere)and the ecu went into defect mode(sets the rpm to approx 2500rpm and you have no throttle control).a temp sensor is rare to completly fail normally just gives false readings.seeing as your temp gauge went down to cold and the ecu went into defect it would suggest a complete break in the circuit.check the coolant temp sensor connector(sensor in the alloy part of the thermostat housing on the end of the head)

 

[mikeherts]

Thanks both! Im not the most technical person under a bonnet, so youll have to bear with me if I sound like a dumb ass.

So if it was that, then Im not damaging the car by driving it? Its just cutting my power because it senses "something" wrong with the car (even if minor) and doesnt want me to potentially damage it?

So basically it could happen again at any time? All the way home, the temp guage was moving about from cold to half way like when it cut out before, but it didnt put the ECU in defect mode again?!

 

[BenR]

id change it fo peace of mind.

Easy change, 2 mins.

 

[JAY172]

.it goes into defect mode if it loses communication with a sensor or potentiometer due to wiring in open circuit or a sensor fault(complete failure).if the sensor is in circuit just reading the wrong temps the ecu would just adopt a injection strategy for the temps it was reading.if this temp isnt the correct engine temp due to a faulty sensor then you get poor running.if a sensor circuit is faulty(open circuit/no sensor output)then the ecu is unable to run the engine exactly right so it goes into defect mode which gives you a set revs so you can limp the car home.

 

[ak_uk]

Finally - someone who has had the same problem as me! Ive had this occur at least once with the rough running and on occasion with the wavy temp guage. Where is this coolant sensor if you are looking under the bonnet?

 

[rocko]

yeah I had this and it was the ECU at fault - replaced under warranty

 

[ak_uk]

Cant be my ECU (at least not the ECU itself) as it happened on my standard ECU and my HP one!

 

[Rick_172]

Dont worry about it. You have a 3 yr warranty. Book it in.

 

[mikeherts]

Errr I dont have a 3 year warranty (import), so Im screwed if it needs a new ECU!! I think what JAY172 and BenR said makes a lot more sense than a whole ECU being at fault. I hope

ak_uk, did you speak to a dealer about it, or did it just go away? On my short journey to work today it was moving about a little bit, but nothing like the other day on the motorway.

I phoned my local dealer who told me they couldnt look at it until 5th April, which is absolutely no use to me, so I think I might have a look myself and see if theres anything obvious. They said I could leave it with them for a few days and theyd look if they got a spare moment, but I cant really afford to be without on a whim that they might get time.

Can anyone give an idiots guide to where to look for this sensor?

Thanks again for all the help!

 

[JAY172]

there is an alloy bracket on the end of the head with quite a few water hoses on it.the coolant temp sensor is screwed into that.

 

[ak_uk]

Mike - They said they couldnt diagnose any problem because I had an IK fitted and the diagnostics were falling over at something not being connected - I think the vacuum powered flap that flips when its cold .

BenR and Jays posts make sense to me. Im in the same position as you warranty wise.

Guys - I havent looked for the sensor yet but is there going to be any fluid loss if its swapped out?

Thanks...

 

[BenR]

Number 20, its on the side of th cylinder head, next you your airbox.

When you take it out there will be some fluid loss.

http://erc.qmuc.ac.uk/cliosport/gallery/full/1079995815__CTS2.jpg

 

[JAY172]

Quote: Originally posted by ak_uk on 22 March 2004


Mike - They said they couldnt diagnose any problem because I had an IK fitted and the diagnostics were falling over at something not being connected - I think the vacuum powered flap that flips when its cold .

BenR and Jays posts make sense to me. Im in the same position as you warranty wise.

Guys - I havent looked for the sensor yet but is there going to be any fluid loss if its swapped out?

Thanks...

that part about the flap is utter b****cks it wont affect diagnostics.have you left the solenoid part connected up or just blocked the pipe up.the only time you might notice any problems related to that flap not working is maybe a slight hesitation when its very cold but only for a few minutes until the engines warmed a bit.ive noticed a very slight hesitation on mine when its really cold since i fitted the ik but it only lasts for a few minutes.the flap just blocks the cold air feed off so the air is drawn in from the other air feed which is under the bonnet behind the headlight.

you lose a bit of coolant when you swap it over.just be as quick as poss so you dont lose much.

 

[mikeherts]

Wow thanks Jay and Ben. So is this something I could easily do myself if I get the part or am I best paying Renault to do it? (assuming that is the problem)

I assume I just get the part from them? Any particular term to ask for to make sure I get the right thing?

Thanks again for your great advice

 

[mikeherts]

Just as an aside and something I just thought of.....

At the time when I hadnt a clue what was causing it and thoughts about fuel, oil and water were going around in my mind.......I checked the water before leaving to go back and it was right on the minimum. I topped it up before leaving and it hasnt gone into limp mode since, though the temp gauge has still fluctuated.

Am I safe to assume this was purely coincidental and nothing at all to do with the problem?

 

[BenR]

77 00 101 968 SENSOR KO 20.90 ---3 x 1

just buy that part, use a deep socket, unscrew it nd replace it as fast as you can. Keep a finger over the hole if you can as not to let air in.

If you take the cap off the expansion bottle, mre fluid will flow out, but you wont get any air moving back into the head.

 

[JAY172]

give the dealer your reg and they have all the details to supply you with the right part.ask for the injection coolant tempurature sensor.you might as well change it yourself as its dead easy.