Emergency mode Volkswagen Golf IV TDI (ALH)

Hello,

Perhaps someone can help me. My Golf TDI with 66kW and engine code ALH has been going into limp mode several times recently. After accelerating hard (around 3000 RPM), the power suddenly cuts out. After restarting, the problem disappears again.

Now, based on information from other forum posts, I suspect the magnetic valve for the VTG adjustment (N75).

Therefore, I measured the voltage at the connector with the engine turned off and also with the engine idling; it was between 6 and 7 volts. However, I measured the voltage with the connector disconnected (was this a mistake?).
Shouldn't there be battery voltage here?

The solenoid valve has a resistance of 17 ohms, so it should be electrically okay.

I was able to easily move the VTG adjustment mechanism by applying suction to the vacuum line.

Today, I was "lucky" enough to experience the problem again, and I was able to take it to a friendly mechanic who could read the error codes directly without having to turn off the engine.
There were 2 errors.
00575 Intake manifold pressure control differential and...
01262 Magnetic valve N75 - Intermittent fault, short circuit to ground.

The first error is likely a consequence of another issue. However, after clearing both errors with the engine running, the first error reappeared immediately (or it couldn't be cleared).

Since my friend is already planning to order all sorts of parts and seems very enthusiastic about it (judging by the dollar signs in his eyes), I wanted to ask if anyone could give me some advice on how I can do further research myself.

Thank you very much.

Holger.

Hello Holger,

First, I would replace the N75 solenoid valve and then see what happens next.
Also, also be sure to check the cables that control the N75 for any signs of wear or damage, such as fraying or being chewed on.

Best regards, Rainer.

Could it also be due to the pressure sensor for the intake manifold pressure?
If the sensor provides incorrect values, the control unit will attempt to compensate, but this can lead to it operating within an incorrect control range.

I would rather not buy the new N75 right away unless I know for sure that the old one is really broken (they probably cost over 100 euros).
How can the N75 be tested?

Hello Holger,

Holger247 wrote:

Könnte es auch am Drucksensor für den Saugrohrdruck liegen?

Theoretically, yes, but I've never heard of a case where the pressure sensor itself was broken. More often, it's chewed-on cables leading to the pressure sensor.
It's more likely that the issue is a simple mechanical clamping mechanism for the VTG (variable transmission gear), but this doesn't seem to be the case for you, as you mentioned it feels loose.
"Error code '01262: Intermittent fault with solenoid valve N75, short circuit to ground.' is unlikely to be caused by a faulty pressure sensor."

Quote:

I would rather not buy the new N75 right away unless I know for sure that the old one is really broken (they probably cost over 100 euros). Wie kann man das N75 testen?

"That's expensive? Hmm, you could try swapping the solenoid valve for the EGR system and the one for the turbocharger boost control as a test."
If the engine control unit displays an error message like "short circuit to ground, EGR solenoid valve," then it's pretty clear what the problem is.
Take the car for a test drive with the swapped magnetic valves and see if the engine still goes into limp mode.

Please pay attention when swapping the solenoid valves and make sure to note which hose goes where; it's best to attach a label .

Best regards, Rainer.

How much smoke does the engine produce within a certain RPM range?
I experienced something similar with excessive soot at 2000-3000 RPM. I had a 'vacuum pipe pressure difference' error (what a word!), but without the relay fault. In my case, it was simply due to cracks in the transition pieces between the pressure and vacuum pipes, which caused air leaks.

Rust doesn't actually occur very strongly.

I'm going to re-check the N75 valve. How can I test it? Can it be tested by a VW dealership while it's removed?

Otherwise, I suppose I can just try replacing the AGR valve.

"I'm also going to verschandeln the EGR valve. Could a stuck EGR valve cause a limp mode?"

Hi everyone,

If I imagine the "normal" circuit of the valve, one terminal is connected to "+", and the other is switched to ground by the engine control unit.

- In that case, the error "short circuit to ground" can only mean that there is no voltage on the energized wire, even though the motor control unit is not currently grounding it.

Possible reasons:

1. Interruption in the supply to the valve, the valve coil, or the wiring harness leading to the engine control unit --> this results in insufficient boost pressure being generated.

"Loose connection or short circuit in the wiring harness leading to the engine control unit can cause excessive boost pressure."

Since the error message doesn't indicate whether there is too much or too little, this is once again a classic case that suggests using an LDA as a mandatory instrumentation for TDI.
--> A quick look at the indicator light when the car malfunctions immediately tells you which direction to investigate.

Without LDA, you're left with only 1551 or VAGCOM to attach, drive around, and hope that you can quickly access the diagnostic tool when the error reoccurs.