P0115 - engine coolant temp circuit

  1. Regular Poster Joined: Aug 2014 Surrey Posts: 275 '57 Vauxhall Vectra CDTI - Daily '02 Saxo VTS - Tu
    #1
    Hi guys

    STILL trying to get the VTS to idle and run properly...

    Idles ok when a bit warmer but revs don't drop straight back down when you blip the throttle, but whether it's hot or cold, if you're in gear it wants to pull itself along at about 2000rpm.
    I've read that it's the coolant temp sensor which would agree with the code reader,

    HOWEVER

    When the coolant temp sensor is unplugged, the car splutters and runs horribly, which would suggest the sensor is actually ok and doing its job properly? Doesn't seem to go into base map fuelling which is strange.

    I have the fan wired to a switch on the dash, would this affect the circuit at all and possibly be the reason for the code being thrown up?


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  2. Central South Joined: Jun 2006 East Sussex Posts: 3105 VTS :)
    #2
    Maybe the sensor is on the way out and giving an incorrect reading.
    Think you can test it with a multimeter.
  3. Regular Poster Joined: Aug 2014 Surrey Posts: 275 '57 Vauxhall Vectra CDTI - Daily '02 Saxo VTS - Tu
    #3
    Quote:
    Originally Posted by Alex View Post
    Maybe the sensor is on the way out and giving an incorrect reading.
    Think you can test it with a multimeter.
    Replaced the sensor, it has fixed it to an extent.... It idles much better in general, however sometimes it does still hunt and sit at 2000rpm. Turning it off and turning it back on, or revving it out a bit usually sorts it out, but looking elsewhere now. Maybe TPS/icv? Manifold was cleaned when it was all put together.

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  4. Saxperience Hardcore! Joined: Dec 2007 smurfland. Posts: 17346 Ex saxo owner.
    #4
    Try cleaning the icv and the throttle body innards.
  5. Regular Poster Joined: Aug 2014 Surrey Posts: 275 '57 Vauxhall Vectra CDTI - Daily '02 Saxo VTS - Tu
    #5
    Quote:
    Originally Posted by stevo67 View Post
    Try cleaning the icv and the throttle body innards.
    ^^^ it all had a thorough clean when it went together a few weeks back. Leaning towards icv then?

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  6. Saxperience Post Whore Joined: Jul 2010 Morley, Leeds Posts: 8469 Civic ep3 type r powered by TDI NORTH
    #6
    Get yourself a brand new genuine stepper for the ICv had problems with a few of them a while back and the problem was mostly cheap eBay "brand new shite"
  7. Frequent Poster Joined: Nov 2009 Posts: 576
    #7
    Coolant and air temp sensors tend to 'drop out' at certain tamps then work again when a bit warmer. It's the most common way for them to fail.
    Did the idle speed fault start just out of the blue or after you had it apart fro some reason?
    If so, you've probably got an air leak.

    Also, check the TPS voltage (or engine 'status' with a scan tool) because if the ECU thinks the throttle is not at idle it comes off the idle control strategy and runs on 'normal' maps rather than running to keep a stable idle at the desired rpm.
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  8. Regular Poster Joined: Aug 2014 Surrey Posts: 275 '57 Vauxhall Vectra CDTI - Daily '02 Saxo VTS - Tu
    #8
    Quote:
    Originally Posted by Chipwizards View Post
    Coolant and air temp sensors tend to 'drop out' at certain tamps then work again when a bit warmer. It's the most common way for them to fail.
    Did the idle speed fault start just out of the blue or after you had it apart fro some reason?
    If so, you've probably got an air leak.

    Also, check the TPS voltage (or engine 'status' with a scan tool) because if the ECU thinks the throttle is not at idle it comes off the idle control strategy and runs on 'normal' maps rather than running to keep a stable idle at the desired rpm.
    It has never idled nicely since I've had it, but never had the 2k problem which is now fixed. Had all new gaskets at build time.

    I'm not sure how I check the TPS voltage in all honesty!!!!

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  9. Frequent Poster Joined: Nov 2009 Posts: 576
    #9
    Quote:
    Originally Posted by smokeandpoke View Post

    I'm not sure how I check the TPS voltage in all honesty!!!!
    You use a multimeter.
    You should have 5.00v (which is the 'reference voltage), 0.0v (sensor ground) and around 0.6v (signal) on the three wires.
    :-)
  10. Regular Poster Joined: Aug 2014 Surrey Posts: 275 '57 Vauxhall Vectra CDTI - Daily '02 Saxo VTS - Tu
    #10
    Quote:
    Originally Posted by Chipwizards View Post
    You use a multimeter.
    You should have 5.00v (which is the 'reference voltage), 0.0v (sensor ground) and around 0.6v (signal) on the three wires.
    :-)
    No I got the bit about the multimeter - the readings above, is that on the plug, or backprobed when the sensor is in?

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  11. Frequent Poster Joined: Nov 2009 Posts: 576
    #11
    Well you can't check sensor readings unless it's plugged in, can you?
  12. Regular Poster Joined: Aug 2014 Surrey Posts: 275 '57 Vauxhall Vectra CDTI - Daily '02 Saxo VTS - Tu
    #12
    Quote:
    Originally Posted by Chipwizards View Post
    Well you can't check sensor readings unless it's plugged in, can you?
    K so I need to get myself a paper clip

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