Pre-heating system

Hello everyone!

Silly question: How can the preheating system determine how long to preheat? Or, is a temperature sensor queried? If so, which one?


Thanks for your responses!

Greetings
Dirk

Hello Dirk,

In my AHF, there is a double-temperature sensor on the cylinder head.
If the measured temperature is low, preheating will occur.

BTW, does anyone know why I have 2 sensors (in a housing with 4 connections) installed, when only one would be sufficient?

Hello, Rainer

Hello Rainer,

Could it be that there is one sensor for the temperature display and another for the preheating control? The temperature display has a resolution of approximately 70-120 degrees, which is quite good and important. The preheating control is interested in a completely different temperature range. When temperatures are above approximately 10 degrees, preheating is not necessary, and when temperatures are significantly lower, the preheating time is correspondingly longer.
Maybe one is an NTC (temperature display) and the other is a PTC...

Greetings

Eike

PS: I also have a 3-pole sensor lying around. It has the part number 1H08594481B and the specification 6-24V. Does anyone know what this part is for?

Hello everyone!
Since this is already about the Vorglühanlage, I just want to add my question...

For quite some time, I've had the problem that my AFB engine (year 1998) is very reluctant to start when the engine is cold. It often takes two or three attempts, or about 5 seconds of 'coughing,' before it finally starts. Once it's running, it runs perfectly (it might be because it has 6 cylinders, which prevents it from 'stuttering'), and it doesn't smoke. In the spring, all six light bulbs were already replaced, as I had experienced the same problems last winter.
What's a bit surprising to me is that the pre-heat indicator light only lights up for a fraction of a second when the KLT starts. Even though the outside temperature is currently +4°C. In fact, it should light up for longer after 12 hours of inactivity (overnight)! I also tried the same thing with another AFB motor (year 00). This glowed for about 3 seconds before...

The most important question is actually whether the warning light indicates the pre-heating time, even if a relay or fuse is faulty or not... if so, it can be assumed that the temperature sensor is faulty!?

In einem anderen Posting habe ich etwas über das Relais 109 gelesen. Ist das in jedem TDi verbaut und welche genaue Funktion hat es? Could it also be a cause of the poor cold start performance, as I have also experienced some issues in the past few weeks when the temperature was still above 10°C...?

Thank you for your help!

Best regards,

DENNIS

Anyway, does anyone know why I have 2 sensors (in a housing with 4 connections) installed, when only one would be sufficient?


one for the EDC, the other for the temporary display in the combined instrument cluster.

My ALH (automatic light heating system) also doesn't glow at the current +2°C in the morning almost at all. The heating element doesn't even light up for 1 second, and I start the engine immediately. It starts perfectly and runs smoothly immediately.

See you, Gremlin

Hi,
To your contributions, I have made the following comments:
the EDC (Elec. (Diesel Control) activates the preheating process after querying the coolant temperature in the dual temperature sensor, if the measured temperature is 4°C or below.
After disconnecting the connector, you can measure the resistance value between pin 1 and 3 of the double sensor. 10°C corresponds to approximately 3500 to 4500 Ohms. 80°C corresponds to a resistance of approximately 275 to 375 Ohms.
Using VAGCOM or similar diagnostic adapters, the 007 display group can also be used to display coolant temperatures. Check fuel and intake air without opening the hood.
Display Group 012 provides information about the preheating time, supply voltage, and other parameters that are important for preheating.

With my transporter (TDI 75kW), I only had one starting problem last winter (at -10 or -12°C), when I had to turn the key twice or three times. Reason: 4 out of 5 light bulbs were defective.
A prerequisite for this eagerness to start is that the injection timing (start of fuel supply) must be set extremely accurately.

1H0 959 481B is a double thermostat, which in the Golf and Passat, is responsible for activating the electric fans in the water cooling system; it is therefore not a sensor (it switches in two stages: 95°C and 102°C).

Relay 109 is consistently found in all VW TDI models and switches the power supply for the electrical engine control via the ignition. It can occasionally cause engine stalling. Newer models can be identified by their gray housing color, with the inscription '109' above! Not 'made in Tunisia'.
Best regards, Jan

Hi,

I agree with Gremlin: Yesterday morning, my MFA showed an outdoor temperature of -3 degrees, while our stationary system in the apartment showed -4.4 degrees. The pre-heating LED was only lighting up for just over one second. The machine started and ran smoothly on the first compression stages – it was, of course, hard as usual when it was so cold, but perfectly round.

The car had been parked for more than 12 hours before, on the street without any protective barriers or ditches.

Best regards,

Jan

Ok, danke!

Thank you too!

Greetings
Dirk

Hi,
I've postponed my visit to the workshop for my Passat (MKZ AFB) a bit longer. At +5 degrees Celsius, it starts with a strong glow for several seconds, and then starts very poorly, as reported by GarfieldMZ here. And after starting, it emits some (with mineral diesel) or a lot of (with biodiesel) white smoke.

So far, I've been worried about deteriorated seals in the ESP. Maybe I should just get the light bulbs checked instead? EZ 01/99, 100,000 km.

Best regards,
Christian

Hello everyone!

I tried to find the root cause of my problem with the poor starting again. I tried starting another V6 TDI with the same starting time (approximately 9 hours overnight) at the same outside temperature to see if it also preheated. The other one only did it for me....
Then I checked with the VAG-COM to see what values the temperature sensors for preheating were displaying for both cars. Mine showed a value of 14.5 at an outside temperature of 9 °C. The outside temperature was even slightly lower than the temperature indicated by the pre-heating sensor.
Now I'm wondering, which one is actually showing the error... shouldn't both values be approximately the same? If it were to show me more, it might explain why he performs so poorly and also why he doesn't seem to warm up at all compared to the other car.

DENNIS

GarfieldMZ wrote:

Now I'm wondering, which one is actually showing the error... shouldn't both values be approximately the same? If it were to show more, it might explain why he performs so poorly and also why he doesn't even get up to speed compared to the other car.

Hi Dennis

IMO, the last sentence is completely correct.

Which one is displaying incorrectly can be checked relatively easily using VAGCOM. Therefore, there should be a value group for each engine, with the temperatures of the coolant, fuel, and intake air.
If the engine is completely {COOL}, then the same temperature should be displayed everywhere, with minor differences of up to perhaps 3° being normal.
If a value deviates significantly from the norm (or is completely nonsensical), that's likely where the problem lies.

Sorry if I'm interrupting, but I couldn't find anything more suitable through the search.

I bought the 35i (manufactured in 1996) with the AFN engine from my previous thread and I've found that it only pre-heats for one second and, as a result, the engine doesn't start until approximately 5 seconds after pre-heating.

Does anyone know which temperature sensor on the 35i provides the signal for the headlight glow function?

I don't have any other diagnostic tools besides a basic reading device in the company (which can only read fault codes and output numerical codes), so I have to measure manually.

Thank you for the information.

Best regards, Rüdi

Hello,

one second at what outside temperature?

Above 5 degrees, no (intact) TDI shows the pre-heating indicator for longer than for the EDC function test (which should be approximately one second), and you can also start immediately without waiting.

So, if it wasn't just very cold temperatures, I would look for starting problems in the forum and not look at the pre-heating system any further.

Best regards,

Jan

Hi

We have been experiencing temperatures in the range of -5°C to -10°C during the testing periods.

I think it's probably the issue with the heater.

Best regards, Rüdi

Hi,

at -5 to -10 degrees and with a cold car (!), he should at least preheat for 5 to 10 seconds. If the display still only appears briefly, then check the temperature sensors.

Best regards,

Jan