Starting problems with the CAY

Hello everyone,

My Polo 5 (6R, engine code CAY, 1.6 TDI) starts very poorly when it's cold, especially if it has been standing in the carport overnight.

It can be said that the behavior is worse proportionally to how colder it gets. This becomes noticeable around an outdoor temperature of approximately 2°C (which is why I had forgotten about it since the last cold snap).

Observations: (temperature tonight -12°C).

- The preheating indicator light is illuminated for the same duration as usual.
- After long organ notes and finally starting up, there is no white smoke.
- Turn the ignition off and on again; the interior lighting dims for only 1-2 seconds.
- No error codes stored.
- All the temperature sensors that I could find in VCDS are showing the same readings; none of them are displaying unusual values.
- When the engine starts, it runs smoothly right away; no cylinder is misfiring.

The first thought is obviously the glow plug. But isn't that supposed to be monitored? No white smoke, no error codes stored...
Remove the spark plugs, disconnect the connectors, and I'd rather not use the H4 bulb trick for now. The 13-year-old plastic is prone to breaking . Unfortunately, I also don't have a clamp meter.
Repeatedly turning on and off (an old trick used by some people) doesn't achieve anything.

Just based on my gut feeling, I would say that the box isn't glowing at all. The only thing that doesn't quite fit is the lack of white smoke.


I would also rule out the possibility of the fuel line running dry overnight, as it is completely temperature-dependent.

The battery is fine, and the starter motor is running smoothly.

What else could I check right now? I'd like to use the laptop to log some data, but when the organ is playing, VCDS briefly loses connection (is that normal? The radio also cuts out for a moment).

I've only had the car since last summer, so I haven't really looked into it before. Therefore, I have no idea how long this problem has been going on.

How can I narrow down the error further now? What should I look for?

Thank you and best regards.
David.

*P.S.: I used to operate a 1Y engine with fuel additives in the "one-tank" system, even in winter. So, I know what starting problems are .

Have you replaced the fuel filter yet?

Hi there,
First, check the glow plug fuses.
The fact that the VCDS loses connection and the radio turns off while playing music suggests a voltage drop.
hg
Herbert.

I haven't replaced the fuel filter, but it doesn't look old yet. I should probably change it sometime though... If that were the cause, the engine would likely start and immediately shut off again, and wouldn't run "normally" right away. Once the engine is running, everything seems fine...

Fuse (50A) is in good condition.

Ich wollte ja die Bordspannung beim Startvorgang mitloggen, aber die Verbindung ist kurz weg. Und dann braucht natürlich VCDS paar Sekunden, Radio geht doch bei allen Autos kurz aus, ich kenne das eigentlich nicht anders. Ist das heutzutage anders und ich fahre nur alte Karren?

My Audi has a Chinese Android system installed, which won't turn off, but it also has a built-in battery.

In the extended measurement data, I found only one value that has the word "glow" in its name.

preheating time: 0.0 seconds

Hello!

You can start with the spark plugs.

A clamp meter would be great.
Maybe ask the electricians at work if you can borrow one; it would need to be able to run on direct current though.

Hmm, I'm not familiar with that car. I wouldn't remove the glow plugs without a good reason. And if I did, I would only do it when the engine is warm.

If I don't want to damage anything, I might expose the glow plug connectors.
and measure the resistance individually.

I think it's probably around 3-5 ohms, that's what they should be.
Certainly, all of them should have a measurable resistance, and they should also be approximately the same.

When you turn on the ignition and the engine is very cold, power should also reach the supply line.

It's not that unusual, actually.
"I once had three glow plugs fail in my Golf, and I didn't realize it until the temperature dropped to -10°C."
At normal temperatures, it started up normally.

docsnydor wrote:

Sicherung (50A) ist i.O.

Hi there,
I don't have it in front of me right now, but if there are strip fuses (attached with two M6 nuts) on the fuse block on the battery, they tend to come loose.
sometimes to hairline cracks
Visually, it's barely noticeable, if at all, but the interruption is there. Or perhaps it only happens sporadically...
Quick check without a test lamp or multimeter: Use a flathead screwdriver to gently press down on the center of the fuse; with a mechanical fuse, you will then be able to see...
Defect due to hairline crack.

Best regards, Richard.

Thank you all.

I measured the resistance of the fuse with a multimeter, and it was 0 ohms.

The annoying thing is how difficult it is to access the glow plug connectors, or how they are "isolated." Everything is neatly wrapped with electrical tape and shoved into designated channels.
And on top of that, everything is stiff and hard in the cold. Just getting the connectors off without breaking them apart is an art in itself...

Hello David.

Quote:

Ich würde ja gerne mit dem Laptop was mitloggen, aber beim Orgeln verliert VCDS kurz ja die Verbindung (das ist normal, oder? Radio geht ja auch kurz aus).

Battery low.

You can also read the current value from the on-board network control unit, but it's likely that the preheating process has already ended by the time you see those values.
It's possible that the engine control unit is already initiating afterglow, and you could compare the current consumption with the ignition on but engine cold to the current consumption with the ignition on and the engine hot. It would be unfortunate if afterglow is also activated in warm engines for emissions reasons; perhaps you can see how the glow plugs are being controlled in the measurement data from the engine control unit.

Without any white smoke, I'm more inclined to suspect a different problem, such as insufficient rail pressure or an inadequate starter motor speed.

Best regards, Rainer.

Thank you again.

If the battery was weak, wouldn't it be impossible for the engine to crank for so long?

I just ordered a clamp meter; I probably could have used one before, even for solar panel installations.
This weekend, I'll continue troubleshooting the issue. It's supposed to get warmer, and at least I'll have daylight while I work on it. I'll let you know if I have any new findings.

Hi.

"Long" is relative; check if you can determine the engine speed during startup using VCDS. Below a certain threshold, the starting process may be blocked depending on the engine control unit.

Also check the fuel rail pressure regulation system, especially the pressure build-up.

Best regards, Rainer.

Hi there.

My first approach would be to check the glow plugs!

Obtained new genuine parts. When the engine is warm, remove and inspect the connectors (as they are more pliable when warm), but replace them immediately.

In a similar case of an AFN (presumably referring to a specific type of engine or device), the symptoms were comparable, and three glow plugs were found to be defective.

An alternative approach would be to check the glow plugs with an infrared thermometer when the engine is cold; this can reveal if any of them are still heating up.

Hi there,

The delivery guy was diligent and already brought the clamp yesterday. Unfortunately, there's very little space between the wiring harness and the GK connector...

I only had a short amount of time, which is why I wanted to measure the voltage directly at the battery's ground cable.
(Surely this should work too? The measurement doesn't have to be precise.)

Result: approximately 20 Å.

At least something is being primed or triggered.

So, could it really be the glow plugs (I'll check that this weekend), or possibly also the "glow plug control unit" (relay)? Apparently, it should be located somewhere within the vastness of the engine compartment...

I had also been considering the idea of using an infrared thermometer. However, it's difficult because you need to aim carefully to avoid hitting the candle connector...

This time, the car was parked backwards in the carport, and there was definitely no white smoke.

It remains exciting. The fuel filter is also being delivered by post today.

VG
David.

20 Amperes during the initial heating phase?

The current must be measured immediately when the power flows, because the current strength decreases over time.

Replacing the diesel filter can save you money for this reason.

The power supply to the candles is phase-shifted and pulse-width modulated (see SSP 420). This aligns with the 20A specification.
hg
Herbert.

I was still thinking about my old favorites.

Things were still alright back then...

Herbert.