hesitation/jerking and fault code 14 (coolant thermistor)
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Thread: hesitation/jerking and fault code 14 (coolant thermistor)

  1. #1
    Fellow Frogger! Wintermute's Avatar
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    Default hesitation/jerking and fault code 14 (coolant thermistor)

    Since I replaced the radiator, I've had an intermittent problem with the car hesitating/jerking. It's like it momentarily loses power and then comes back.

    I checked the fault codes and had 51 and 14, 51 is oxygen sensor and after inspecting I found that the wiring on the white connector was bare so re-insulated that and cleared the fault codes.

    It ran fine for a week but started up again today. I read the codes, and only the code 14 now (coolant thermistor).

    It seems unlikely that a fault with the coolant themistor would cause this sort of problem, but I'm open to suggestions! I'm not actually sure which one it is.

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    I've attached a diagram showing the sensors I can see. The blue one is where the blue arrow is, the other one is where the red arrow is. This one however looks green to me, not maroon. This one is new and was replaced a couple of years ago when the fans were not working. The blue one is attached to the temp gauge on the dash.

    I don't think that the ECU would monitor the blue one would it? Though the naming of it is in line with the fault code.

    I had a similar fault to this about 15 years ago (though it was more severe, with the engine completely cutting out momentarily making it totally undrivable. That fault turned out to be a rubbed through wire in the loom that was shorting on something when the engine moved under power.

    The car is idling fine. The problem will happen either on accelleration, or driving at a constant speed.

    I guess it could be a coil starting to go, but that normally just results in running on three cylinders when the car gets up to temp.

    edit: oh and the K light is NOT coming on. Also probably temp related, I haven't noticed it happen before the car gets up to temp.

    Tony.
    Attached Thumbnails Attached Thumbnails hesitation/jerking and fault code 14 (coolant thermistor)-sensors.jpg  
    Last edited by Wintermute; 21st February 2015 at 10:40 AM.
    306 S16 1995 black
    Morris 1100 1965 green

  2. #2
    1000+ Posts lion5's Avatar
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    no i had the exact same problem on my 206, slightly different symptoms but still that underpowered feeling

    replaced the coolant temp sensor and it was fine after that. pop it out and give it a clean, that's all it might need. overtime residue buildup on them can cause them to not sense as well.

    you could check what resistance is meant to be on the thing when they're cold/warm just to give you a gross idea if it's really buggered. I didn't need to do it as pp2000 showed live readings. temp sensor was spitting 55 degrees whether the engine was fully warm or cold

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    Fellow Frogger! Wintermute's Avatar
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    Thanks Lion, I took my daughter to art class this morning, the car was a pig. The really odd thing is that when it is playing up it seems to be a lot more responsive/willing to go (except for the jerks/surges). On the way back it was still doing it, and the temp gauge started to indicate overheating. temp gauge was getting close to 110, the traffic was terrible, stuck on paramatta road in the middle lane. I suspect the fans weren't coming on. I got off paramatta road and moving again and temp came down to about 95ish. after a while the jerking stopped and the temp went back to normal 90 degrees. When I parked the car I just let it idle, fans came on at 92 and brought it back to 90, behaved perfectly....

    I did look at the blue sensor last night and it IS covered in oil. I will take it off and give it a degrease. I think from memory there is actually a third sensor on the front, but I don't think it is accessible without taking off the throttle body (and maybe even the inlet manifold). That may be the maroon one. I suspect that service box is telling me lies and there are actually three sensors, some stuff I've seen on other forums says that there are three, blue, green, and maroon. with green being one that tells the ECU the temperature, maroon the Bitron, and blue the temp gauge/overtemp light.

    Very annoyed that it is so intermittent!! But I have also been thinking lately that the car does seem to be underpowered, so it seems I do need to replace a sensor, the question is though, which one?

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    1000+ Posts Andrew Ch's Avatar
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    I have had similar problems with a 205 years ago and it turned out to be an alternator on the way out. It was fine at idle though so might be worth a test if it turns out to be non sensor related....

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    Interesting on the Alternator. Mine was rebuilt maybe 5 years ago, but worth checking. Might be an over-voltage. I actually do remember having an issue (although the K light came on then) where I had a loose negative battery terminal. when I hit bumps the engine car would lurch (like it is now) it turned out that when the alternator lost it's negative to the battery it would cause a voltage spike that upset the ECU.

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    OK I've degreased the blue plug, and I checked the voltage with the engine idling and also with some revs. Constant 13.7V so it looks like the regulator is working fine. I also checked the faults again after my pig of a run along paramatta rd, and the 51 had returned (O2 sensor).

    I decided to take those connectors off and give them a good spray with the CRC CO contact cleaning spray, and I also pulled out the ECU and sprayed the connector and pins for that as well. Will go for a drive a bit later and see how it goes, but won't hold my breath.

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    1000+ Posts Andrew Ch's Avatar
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    Good luck...

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    Haha it's worse!! I think the idle control valve might be the problem. I shifted it out of the way when I did the radiator. Perhaps upset it.

    Took it for a drive, it started to play up within a minute or two. When I got home I decided to see if I could get it to do it just revving in the driveway. I started poking around down near the coolant sensor (rear one) when I pulled on the wires the revs increased slightly and the car ran more smoothly. after doing this a couple of times it started running worse. what I noticed was when it hesitated there was a quite a loud sssshhhh sound sucking sort of noise. Pretty sure it is the idle control valve. I tried blocking off the airflow to the throttle body and the idle slowed down, after I stopped piching the tube revs went up and then down, but runs like a dog now. Probably need to reset the ECU again, as it was still learning, and has probably programed an invalid parameter!

    Will have a look at the back sensor plug tomorrow.

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

  9. #9
    1000+ Posts Andrew Ch's Avatar
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    I hate auto electricals !!!!

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    On the earlier models there is an throttle stop switch which is located on the rear of the T/B, infront of the temperature sensors on the thermostat housing. It is held on by two screws (left and right) and is designed to be 'moved' and the screws tightened so the switch is 'on' when the the T.B butterfly is in rest position. Once the T.B butterfly moves a slight touch, the switch turns 'off' telling the ECU to increase fuel to the engine as it's in 'run' mode and not 'idle' mode. Same switch also activates the operation of hte IACV value (the big silver thing with hoses connected to it).

    It might have been knocked when you did the radiator.

  11. #11
    1000+ Posts lion5's Avatar
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    yes that loud sucking is precisely what I heard. It felt like a huge delay in response to the throttle, after it was all fixed, in my case i reasoned that the suck you hear is because fuel timing is out of whack as the sensor says the temperature is X so the ECU responds by retarding spark, and fuel injector pulse width and all this other shit - so you hear engine vacuum first, until fuel gets injected by which time combustion, revs, things moving drowns out the sound of the vacuum.

    But you seem to be narrowing in on it. Don't forget it could be other stuff combined. My problem was also with an air temp sensor, but majority was fixed with that sensor.

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    I have taken the battery box out now. Got at the rear sensor. Have cleaned it up as it was also covered in oil. whilst looking around I also found that the wires on the crank angle sensor plug are bare. Will need to have a look at what I can do with that too, as even if it is not contributing to the problem, it probably soon will be.. it is in the space I was wiggling wires around so I suspect it may have been helping make things worse yesterday.

    I'll also have a look for the switch on the throttle body!

    edit: I forgot to say, I measured the resistance of the sensor (in place) and it is reading around 1.9K which seems about right as the infra red Thermometer says 27 deg C. (going off the info here http://www.306gti6.com/forum/showthr...d=80340&page=1) I probably should really take it out and test it in different temp water though.

    Tony.
    Last edited by Wintermute; 22nd February 2015 at 01:53 PM.
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  13. #13
    1000+ Posts lion5's Avatar
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    why were they covered in oil in the first place!

    what about your TPS sounds like that could be loose or buggered, check the cables for that and or the voltages across - open, closed and medium throttle. It could be reading ok closed, hence OK idle, but shitty elsewhere?

  14. #14
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    Cam cover seal (did it recently but didn't clean up the mess....) was the cause of the oil problem.

    I can check the TPS. I replaced it about 2 years ago (figuring it was worn after 18 years!!) The crank angle sensor wiring is worrying me at the moment, I might need to splice in some longer wire to the loom and redo the plug (that's the worrying bit, not sure where I could get one). I'll try to get the rubber boot off it and see if I can re-insulate the existing wires first though.

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    This is really starting to piss me off!! Put everything back together. took it for a drive, everything seemed fine.

    decided to give it a boot with the throttle to check for lag. car starts then lurches, then almost bunny hopping no power had to pull over and put the hazzard lights on. Sat on the side of the road, trying to get the engine to rev, after a minute or so it decided it would so reved it to about 5K a couple of times, no problem. decided to turn off the hazards and take off. Goes like a scalded cat! Much better than it has for ages. Goes fine the rest of the way home, but when I pull into the drive way temp gauge is heading for 110 again. Check and fans not working.

    Turned it off, read the fault codes, this time 52, 53 and 14. 52 is mixture control, 53 is battery voltage, and 14 is the good old coolant sensor.

    The battery is getting on in years (about 7 or 8) but not showing any signs of problems, apart from running down due to too many short runs. I tested it with engine off at 12.6V..

    Maybe I should just get a coolant sensor and replace it and see how it goes. I'm starting to lose patience!!

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    Another data point. This morning on the way to the station the car was misbehaving pretty much from start (ie cold). Another way of describing the problem might be "hunting on steroids".

    I pulled over and disconnected the bitron coolant sensor. Fans came on full speed (which is the expected behaviour) so it looks like the Bitron is working. Fans should have been on but were not before I took the plug off the sensor. Got back in the car, it accelerated well and then jerked again. So it looks like there *is* a secondary issue. ECU should be running off standard params when the coolant sensor is disconnected.

    I'm now suspecting the plug on the camshaft sensor. The plug on it is actually broken (bottom half has split off) it is attached but can wobble around. I have noticed that bumps in the road can cause the onset of the problem.

    The other thing (after much searching) that could be an issue is a vacuum leak. The one thing I am really not keen on it being is the map sensor, as this is built into the ECU.

    Looks like I need to try and get a plug for the Cam sensor, and a coolant sensor as the next steps.

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    1000+ Posts Andrew Ch's Avatar
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    And once again....good luck : )

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by Wintermute View Post
    The one thing I am really not keen on it being is the map sensor, as this is built into the ECU.

    Tony.
    Never had a map sensor malfunction, but have had a split hose that opens up on corners.

    What that will do will majorly alter the fuel map and could very much be your issue.

    Can you get some real time diagnostics???

    The culprit should show itself immediately, be it TPS, Map sensor, Coolant sensor or Cam/Crank angle sensor.

    Maybe the MAP sensor and TPS faults are ganging up to produce what the computer thinks is idle, or WOT when it isn't at either of those conditions.

    Jo

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    I'm leaning more and more to an air leak somewhere. Unfortunately I don't have access to real time diags. I am also thinking I should replace the battery. Was really sluggish this morning starting, hoping the car starts tonight when I'm on my way home! Battery voltage error code did come up once, and it is 7 or 8 years old! Could be one of the plates arcing (fits with the bumps)..

    But the reason I'm thinking vacuum is that it seems to be worst either a) on constant throttle, or b) on quick changes of throttle... ie what should be constant vaccuum or changes from low to high vacuum.

    I've had a problem with the car hunting a little (not often) for years. I asked about it once and was told short of getting a remap of the ECU there was nothing that could be done about it (which I thought was sus but since it wasn't bad I didn't follow up further). It may be the same issue just it has gotten a whole lot worse...

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

  20. #20
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    I *may* have found the problem (but saying that It will now probably come back.

    I was slowly eliminating things. I checked all the vaccuum hoses the other night, nothing. I pulled the coil cover off and found I had oil in my plug wells (just up to the top of the metal part of the plugs. Did my best to mop it up but no change. (this is a result of not being able to get new plug well gaskets when I did the cam cover gasket).

    yesterday I drove home with the oxygen sensor disconnected, no change (traffic was heavy and once the car got hotter was being a pig).

    I disconnected the idle control valve and it would still do it when I revved.

    I cabled tied the cam sensor connector togther it is now fitting tight as a drum. No change.

    I noticed that the injector wiring was going over the vacuum punp and that the convoluted tubing was completely worn through and the wires resting on the vaccuum pump. I insulated them up, put on new concoluted tubing and routed around the pump rather than over it.

    Today on the way to the station, not a single instance of playing up. Really hoping this was it. I couldn't see any rubbed through wires but there just may have been a tiny hole that got worse as the insulation heated up.

    here's hoping!!

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

  21. #21
    1000+ Posts Andrew Ch's Avatar
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    We all have our collective Ozfrogs fingers crossed for you.......

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    Fellow Frogger! Wintermute's Avatar
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    Seems luck is not on my side

    The car was fine Friday. Also fine for a 30 minute drive in traffic on Sat Morning. after an hour and a half the return journey was started and shortly into it, three giant lurches, then no problem for the rest of the trip.

    Sunday no problem.

    Yesterday and today pretty much every time I drive the car it is having some hiccups.

    There aren't too many things left for me to try. The weird thing is every time I probe and prod around the symptoms change somewhat.

    Things I haven't ruled out:

    crank angle sensor
    TPS
    knock sensor (new one was put in about two years ago)
    ECU
    Air intake temp sensor
    Cam position sensor
    Battery

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

  23. #23
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    Yesterday I disconnected the Air Temp Sensor and went for a drive, if anything it made it worse. Which I gyess could be a clue. I had checked the resistance and it seemed to be consistent with the current ambient temp of the throttle body.

    I also had my suspeicions about the TPS so I disconnected that. Man does it have trouble idling without a TPS!! went for a drive and still had the problem.

    One thing is it seems not to be a problem with the throttle wide open, which on searching motronic 3.2 ecu problems turned up a post on a 911 porche which said that if the problem goes away at WOT that it is probably a sensor as the ECU ignores most sensors at WOT... This seems a bit tentative though.

    I started to search for what are the symptoms of a faulty X sensor. TPS, crank angle sensor and cam sensor can apparently all cause my symptoms.

    I guess I really need to replace the plug on the camshaft sensor rather than just cable tying it together.

    The quest is ongoing...

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    Have you checked the fuel pressure. Faulty fuel pump?

  25. #25
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    No I haven't, I'm not sure how I would do that... pressure gauge with a t piece in the fuel line? I wondered about the little silver vaccuum thing on the injector rail as well, I don't know what it does...

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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