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My SDI 9N1 POLO has problems to cool start.
Mornings with external temperature of 12 degrees the glow plugs do not come on.
only when engine starts then. they start to work and post heating is ok


Things that I have changed:

4 New ngk glow plugs, new 103 relay.

Some people tell me that I need to change the coolant temperature sensor, but vag-com show like temp sensor is ok.
Any Idea?

Is VAG-COM showing that the engine coolant temperature is roughly the same as that of the car's surroundings, or is VAG-COM showing that the engine coolant temperature sensor is not logging a fault. The engine sensor could be reading 20C away from the actual temperature, but not logging any faults.

Thanks friend, Yesterday I changed the sensor for a new FEBI BILSTEIN 29318 Sensor and..... Same problem.
This is a nightmare!!! what more can I change? now all is new and glow plugs do not come on, only come on when the engine it's just throttle running (post heated mode)

Have you changed the ambient temperature sensor (Not the coolant one)

Thanx for your help , yes I had change G62 (Coolant temp sensor) but now a technician of SEAT tell me that it is possible the car has low rotation speed of starter motor

Can that be the problem?

Is there a way of overriding the glow plug control so that you can manually select the glow plugs during a 'cold' start ? just for fault finding.
I remember a problem with Vauxhall 2.0 dti engines where the glow plugs did not come on until a ridiculously low temp (+4 c ?) and there was a well known modification for older cars to fool the glow plug circuit into thinking that the ambient temp was below -2 and therefore the glow plugs would always work on any 'cold' start.

A slow rotation of the starter motor will not help cold starting but it would not stop the glow plugs working either !

Yes, I just remove the plastic case of relay and during 6 seconds I push the armature of relay, then glows come on and then the engine starts perfect.

From the workshop manual

Pull the 2 pin connector off the coolant temperature sender (g62) to simulate a cold start and see if they work

Wiring diagram.

The trigger for the relay comes from J248 - the diesel direct injection system control unit (which is actually, the engine ECU)

Yes, when I pull off g62 connector and switch on the ignition I can ear the glow relay "click" sound and glows start to heating.
Then another question rape me, if the ambient temperature is not cold (I live in spain) must glows come on always or only when ambient temperature is under 4º celsius (48 fahrenheit)?????

The temperature has to be below a certain level. I’ll check what the threshold is

Manual says below 40 Fahrenheit (approx)

This is what I meant about the vectra modification,it involved a push switch in the car to operate a relay and resistor in the CTS circuit so that the ECU is getting the correct ohms value for - 1c no matter what the ambient/water temp is and therefore the glows operated on every cold start.
I fitted it to my old vectra 2.0 dti and it really improved the starting - once the engine fires you just release the push button and the system works as normal.

You could easily just add a push switch with a relay in line with the existing relay to energise the coil, or another 103 relay in line with the existing just triggered from a switch using the same input and output on the load side

At the moment I push relay with my finger see