Passat - V.W. Emissions - ColinJ

Can anyone help me try to help me resolve my problem,i have 53reg 04 diesel passat estate,i have a malfunction warning light coming on in the center of the speedo also another warning information on the computer saying " WORKSHOP EMISSIONS".

I had fitted a new temperature sensor fitted but that as made little differance,any help would be appreciated.

Colin

Passat - V.W. Emissions - Peter D

A diagnostic read will indicate where the fault it. Regards Peter

Passat - V.W. Emissions - ColinJ

Peter. Had a computer on the motor last week but that read the fault was a temperature sensor.

Colin

Passat - V.W. Emissions - 659FBE

The coolant temperature sensor is by far the commonest cause of the EML appearing - without any other obvious symptoms.

The Bosch software is clever in that fuel temperature is used as a substitute value for coolant temperature (with a scaling factor) when the CTS fails. All of the original black-bodied sender units will fail as VAG, in a burst of engineering brilliance, filled them with rock hard epoxy resin.

The result is that after a few hundred thermal cycles, the brittle thermistor elements crack due to thermal stress and fail open circuit - usually the one for the engine management system which has the higher resistance.

Ensure that the replacement sender has a green plastic body and is not made in China. There are loads of good German replacements around (GSF sell them) which cost about £17. The part number of the later pattern sender is 059 919 501A. It's wise to change the "O" ring seal - which usually sticks in the head. Hook it out with a small right angled screwdriver.

659.

Passat - V.W. Emissions - ColinJ

659

The one fitted last week was from VW and it was the green one with a new o ring washer Cost £32.

Cheers

Passat - V.W. Emissions - 659FBE

It's probably about time for another diagnostic check - but the replacement CTS may not be above reproach. For example, I have found some genuine VAG parts such as fuel filters are now made in China with (to put it politely) variable results. One such filter would not seal correctly around the thermostatic "T" due to the bore on the filter can being out of shape. The resulting intermittent bad starting has not endeared the vehicle owner to VAG - when I found the reason for her. As the Chinese are making CTS units for this engine (Google the part number), the VAG bean counter division may well have found them.

Access to the CTS is not good on the Passat but if you can make a slave lead or check at the engine disconnect panel you can check the resistance. The "A" thermistor has brown/blue and brown/yellow leads, and the "B" brown/white and brown/grey.

With the coolant at 25 deg C the instrument panel thermistor ("A" terminals) should measure about 1150 Ohms and the ECU thermistor about 2k55 Ohms.

The problem with these wretched things is that they fail intermittently when the thermistor element cracks and usually read OK when cold. A very brief open circuit as the coolant heats up will trip the EML.

If you're paying a garage to do the work, I would (personally) fit another new CTS first as it's an easy DIY job. If it fixes the fault, get a refund for the VAG one.

It takes a couple of runs with a good CTS to clear the EML.

659.

Edited by 659FBE on 24/07/2011 at 23:50

Passat - V.W. Emissions - ColinJ

659. Thanks for you help i will try another CTS.

Colin

Passat - V.W. Emissions - ColinJ

659. Changing the CTS as not made any difference to the malfunction warning lights,seems OK when first changed then as soon as the engine gets hot the warning lights come on,been told it could possibly be the wiring to the coil.

Colin

Passat - V.W. Emissions - 659FBE

"been told it could possibly be the wiring to the coil"

It's a diesel.

OK, time to take it to a good independent (not the provider of the information above) who has the VAG diagnostic software (or a clone) for a full diagnosis, together with the understanding to use it. A CTS is about the only thing I'd change "on spec" if it's a black one.

Hope it's a cheap fix - let us know what it was.

659.

Passat - V.W. Emissions - ColinJ

659. It is the temperature sensor that goes to the ECU but struggling with the part No at the moment.

Passat - V.W. Emissions - 659FBE

The PD diesel control system is complex and there are several temperature sensors. The two which most frequently cause trouble are the coolant temperature sensor and the fuel return temperature sensor. The coolant sensor is the more likely to fail.

The Bosch software incorporates reversionary measures to enable the engine to run if either of these fails - and it's so good that you probably wouldn't notice a drop in engine output. A failure will set a fault code and illuminate the MIL which will go out when you have fixed the fault. The code will remain stored until you clear it.

The coolant sensor was subject to a (very necessary) redesign as the original black ones were potted in hard epoxy which caused thermal cycling damage.

Original black: 078 919 501C

Replacement green: 059 919 501A (This is a direct replacement).

I hope you get it fixed without too much grief - if you seek advice, make sure your advisor knows how the system works.

659.

Passat - V.W. Emissions - jc2

Bosch have a number of Asian factories-not all their parts are German.

Passat - V.W. Emissions - ColinJ

Thanks both

Passat - V.W. Emissions - Padders

I have a similar problem I have an 06 Passat diesel estate and the 'Exhaust Emissions' light has been on for about 2 years!! My local garage have interrogated the computer on numerous occasions and it always suggests that the glow plugs have a problem...so they were replaced initially....then the relay to them.... then the glow plugs again...and finally the garage replaced part of the loom as they told me this often went wrong and sent false messages to the computer. That lasted less than 24 hours before the light came on again. The best we have done is to get it to stay off for about 2 months.

The car starts and runs beautifully and I have not the slightest doubt that the glow plugs are fine - for instance, it started easily all last winter in that cold weather and was standing outside. if anyone has a shortcut to the probelm I would be delighted as the cost of getting nowhere is probably £350 + so far!

Padders

 

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