VW Polo 1,4cc No Start When Hot

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VW Polo 1,4cc No Start When Hot

Postby antreas26 » Mon Apr 07, 2014 11:13 pm

CTS.JPG
Good Coolant Temp.Sensor.psdata
(565.51 KiB) Downloaded 198 times
Bad Coolant Temp.Sensor.psdata
(572.95 KiB) Downloaded 193 times
Hi Guys.This is a VW Polo 1,4cc,2002 model with a BBY 16v engine.Customers complaint,the car cranks good but won't start
when hot (normal temperature).He left the car for further investigation.There was no check engine light on.With the scanner (VCDS) hooked up,there were no faults.The customer also told me that when the car is cold (on the first start) it always starts without problem.I hade a hunch that the coolant temperature sensor would be faulty,causing this problem,so i had the Pico on channel A hooked on the sensor and on the scanner i went to measuring blocks No1 monitoring what the ecu reads from the sensor.Started the car and for 20 minutes it was fine.Stopped it for 5 minutes and tried to restart but the problem was there.No start,the pico was showing 4,88 volts and the scanner -25 Celsius.So the ecu thought that the car was at North Pole flooding the system with petrol.The car started very hard after about 1 minute and when the sensor dropped to 1 volt (normal).You can see it very clearly in the psdata file.Changed the sensor with a new one and monitored again the same way as before to confirm the fix.I also upload a photo of the sensor that made the fuss.
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Re: VW Polo 1,4cc No Start When Hot

Postby Steve Smith » Tue Apr 08, 2014 2:39 pm

Many thanks for the information and sharing the scope traces which provides undeniable evidence to the customer. This also highlights the additional use of the scope for monitoring signals over long time periods, as we tend to forget how useful this feature is. Whilst we know the scope can take millions of samples at lightning speeds, we don't always need this amount of data or processing power and this is a perfect real life example.
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Re: VW Polo 1,4cc No Start When Hot

Postby Liteace » Wed Apr 09, 2014 12:40 pm

That particular type of sensor caused a non start problem on 99% of VAG's it was fitted to, I think its a little bit of overkill timewise scoping it when you can see the problem in the live data.
Quick test unplug it, if it starts then you've saved 10 mins and can move on to the next one
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Re: VW Polo 1,4cc No Start When Hot

Postby antreas26 » Sat Apr 12, 2014 10:30 am

Well Liteace i dont think that scoping the sensor for 15 minutes is a overkill timewise.You will get paid for your time.For me
being accurate diagnosing the problem by scoping with Pico in the front door and using the scanner at the back door at the same time,mostly saves time and money.
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Re: VW Polo 1,4cc No Start When Hot

Postby Robski » Sat Apr 12, 2014 12:46 pm

Live data (PCM/IC) > Infrared thermometer > disconnect & live data again (neg reading,confirms wiring) = <15 mins surely ?
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Re: VW Polo 1,4cc No Start When Hot

Postby Dave Hill » Sun Apr 13, 2014 8:37 pm

Liteace wrote:That particular type of sensor caused a non start problem on 99% of VAG's it was fitted to, I think its a little bit of overkill timewise scoping it when you can see the problem in the live data.
Quick test unplug it, if it starts then you've saved 10 mins and can move on to the next one


I could not disagree more with that comment!

It only takes a moment to hook the scope up & leave it running, gathering data. Whilst it is doing so, you can busy yourself on another job.

Although I agree that these sensors are a very common fail item, I would not want to sit looking at live data, waiting for it to "glitch". I would likely just swap it out anyway, but there are occasions where I might need to demonstrate the test procedure & factual evidence of the failure.

It is a shame to see folks being knocked for posting about their workshop experiences & it does little to encourage others to offer their findings to the group.

I would also add that I don't recall a single instance of a coolant sensor fail, causing a non start on a VAG motor.
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Re: VW Polo 1,4cc No Start When Hot

Postby Robski » Sun Apr 13, 2014 9:22 pm

It is a shame to see folks being knocked for posting about their workshop experiences & it does little to encourage others to offer their findings to the group.


No knocking of scope use from my comment Dave, mine was just aimed at the time aspect.
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Re: VW Polo 1,4cc No Start When Hot

Postby Liteace » Sun Apr 13, 2014 10:31 pm

Dave Hill wrote:
Liteace wrote:That particular type of sensor caused a non start problem on 99% of VAG's it was fitted to, I think its a little bit of overkill timewise scoping it when you can see the problem in the live data.
Quick test unplug it, if it starts then you've saved 10 mins and can move on to the next one


I could not disagree more with that comment!

It only takes a moment to hook the scope up & leave it running, gathering data. Whilst it is doing so, you can busy yourself on another job.

Although I agree that these sensors are a very common fail item, I would not want to sit looking at live data, waiting for it to "glitch". I would likely just swap it out anyway, but there are occasions where I might need to demonstrate the test procedure & factual evidence of the failure.

It is a shame to see folks being knocked for posting about their workshop experiences & it does little to encourage others to offer their findings to the group.

I would also add that I don't recall a single instance of a coolant sensor fail, causing a non start on a VAG motor.


Im not knocking scope use either, all I said was:

"I think its a little bit of overkill timewise"

Pico is a must for diag work, I also 100% agree with you, there are occasions where we might need to demonstrate the test procedure & factual evidence of the failure but most of the time the customer don't give flying, not interested & all they do is moan about the price of the repair.

You say:

"I would also add that I don't recall a single instance of a coolant sensor fail, causing a non start on a VAG motor"

is a VW Polo not part of the VAG group ?
I think every Seat Ibiza & Cordoba + VW polo & Golf they made from about 93 up to 03 was fitted with that type of temp sensor and 99% of them failed causing a non start when hot problem, we've changed 100's of them
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Re: VW Polo 1,4cc No Start When Hot

Postby Dave Hill » Mon Apr 14, 2014 7:47 pm

Liteace wrote:
Dave Hill wrote:
Liteace wrote:That particular type of sensor caused a non start problem on 99% of VAG's it was fitted to, I think its a little bit of overkill timewise scoping it when you can see the problem in the live data.
Quick test unplug it, if it starts then you've saved 10 mins and can move on to the next one


I could not disagree more with that comment!

It only takes a moment to hook the scope up & leave it running, gathering data. Whilst it is doing so, you can busy yourself on another job.

Although I agree that these sensors are a very common fail item, I would not want to sit looking at live data, waiting for it to "glitch". I would likely just swap it out anyway, but there are occasions where I might need to demonstrate the test procedure & factual evidence of the failure.

It is a shame to see folks being knocked for posting about their workshop experiences & it does little to encourage others to offer their findings to the group.

I would also add that I don't recall a single instance of a coolant sensor fail, causing a non start on a VAG motor.


Im not knocking scope use either, all I said was:

"I think its a little bit of overkill timewise"

Pico is a must for diag work, I also 100% agree with you, there are occasions where we might need to demonstrate the test procedure & factual evidence of the failure but most of the time the customer don't give flying, not interested & all they do is moan about the price of the repair.

You say:

"I would also add that I don't recall a single instance of a coolant sensor fail, causing a non start on a VAG motor"

is a VW Polo not part of the VAG group ?
I think every Seat Ibiza & Cordoba + VW polo & Golf they made from about 93 up to 03 was fitted with that type of temp sensor and 99% of them failed causing a non start when hot problem, we've changed 100's of them


Fair enough.

It just looked like the guy was being put down for his efforts.

Funny how things come across in the written word hey! :wink:

Have a good week.
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