open/closed loop ecu

how can i see when my A4 1.9 tdi goes in the
closed loop regulation ?
i'm using vag-com.

( i know that when the lambda sensor is at his
working temperature, this should start the
closed loop ... or am i wrong ? )

if true,
how long does it take to warm up the lambda sensor ?
or... is it also watching at the water/coolant temperature ?

thanx for reading/answering.
greetz

Diesel engines do not have lambda sensors (a.k.a. oxygen sensors). They run lean ALL the time, and hence, a lambda sensor serves no purpose. Take a look at your exhaust system ... you will find NO sensors at all anywhere! (Exception, '96 Passats have *temperature* sensors at the catalyst, but this system was later abandoned.)

Air/fuel ratio is not under closed-loop control in the same sense that it is with a gasoline engine.

Please note, the amount of air going into the engine is under the closed-loop control of the MAF sensor and EGR system ... but it's not measuring air/fuel ratio, the required amount of air is purely a mapped open-loop parameter.

thanx GoFaster !

i never noticed there was no oxigen sensor
(never knew that was onley equipped at fuel systems)
that closed loop question rised because of some things that
i wondered why...

1) after starting car, after abt 2 minutes i hear
a relay 'click' under the dash

2) the coolant temperature never rises above 78 degrees cel.
( therefore in my question abt start closed loop
before , but now already answered)
ps: thermostat changed...no diffrence.

3) little less power 'boost' latest weeks.

and this all, my consume is abt 6 liter/100 km
(i'm an easy driver, so, no burnouts here )

Click about 2 minutes after starting the engine is probably either the glow plugs switching off, or related to the charging system (I have discovered on mine that the alternator doesn't start charging until after the engine has been running for a couple of minutes, and no doubt, there is a relay involved with this). All of this is not an issue, it's all supposed to be like that. (Worry when it STOPS clicking!!)

If the thermostat is okay, but either the gauge or the VAG-COM show low coolant temperature, then the coolant temp sensor is probably bad, which may be related to other issues ...

hi,

example;
the vag-com says 88°c
the gauge says ~ 77°c
the acc/thermoclima (code 49) displays ~ 77°c

the instruments output test with vag-com
displays all gauges nice in the middle

so, i suppose the gauge is right ?
if the vag-com is right (88°c) why does the
gauge meter stand at abt 77°c ?
what shall i believe... the vag-com or the acc/display ?

i'm a bit confused here...

ps:
a while ago, i measured the cold/warm resistance
of the coolant sensor, that was ok with the results
conform a dutch manual i have ( i have no bentley manual )

thanx.

The single sensor housing contains TWO SEPARATE sensors - that's why there's 4 wires going to it - one sensor for the instruments, another for the engine ECU. Your coolant temp sensor is out of spec. Replace it ... or don't worry about it, since the engine ECU is getting correct information. It's simply not being displayed correctly, and if you can live with that (I would!) then don't worry about it.

GoFaster,

i'd like to thank u for all these answers,
therefore,

my best regards,
gelly