TDI 90PS ALH: Strange Error Codes Explained

My friend is having the following problem with his Golf IV TDI 1.9L/90HP.
Engine code ALH.

The performance simply drops without warning when accelerating in the higher RPM range.
The engine speed is increasing, but there's no noticeable increase in power.
He then reached a speed of 100 km/h at 3000 RPM.
Normally, you would expect around 2000 RPM at 100 km/h.

When reading the error memory, the following result is obtained:
Intermittent boost pressure regulator fault.
Confused about which hose to use?
"Error codes displayed!"
But nothing has been changed yet, everything is as it came from the factory, and it was working before.

Despite replacing the boost pressure regulator, there is no improvement!

If that happens on the highway, he does the following.
Depress the clutch pedal.
Ignition off.
Restart.
Error gone!
And it's working perfectly again!!!

What on earth is this?
Has anyone ever experienced something like this before?

Does anyone have any helpful advice for us?

"Thank you very much!"

If the engine is really revving up at a constant speed, there's likely a problem with the clutch. The turbocharger pressure regulator can't change the fixed relationship between engine speed and vehicle speed.

I see it that way too, but the clutch is fine.
No loops, nothing.
There might be a problem with the electronics.
Is it suggesting that you are displaying false values?

Hello,
"It sounds like it's going into a limp mode, which means you only have minimal power. The boost pressure then drops to around 0.3 bar, at least in my G4 AHF. I've occasionally had similar problems at full load on the highway, where the power suddenly disappears. After a restart, everything is usually okay again. In my case, this mainly happened when the auxiliary control unit was set to its maximum setting, combined with a 50/50 mixture of fuel and oil. Then, after a prolonged period of full load (without active intervention), the boost pressure would exceed 1.2 bar, and after about 5 seconds, it would go into limp mode."
That doesn't explain the strange phenomenon regarding the speed, though, does it?
Without VAG-COM and without LDA, it will probably be difficult to diagnose.
Sure, here is the translation of the text from German to English:

"Hello"
harald

That's the strange thing...
The VAG Com always shows this strange entry!
It is powered exclusively by diesel.
Andere Frage zum Pöl... Is yours a PD?
I was told that it's not possible with PD.


Best regards,
Ralf

It's still not entirely clear whether the speedometer or the tachometer is displaying incorrect information, or whether the engine is actually revving up at a constant speed.

According to the first thread, the DZM (likely referring to a device or system) is showing increasing values, even though the speed remains the same.

(A DZM cannot rev up; at most, the engine can.)

Now, please specify exactly what behavior is considered abnormal.

m

Does the Golf perhaps have an automatic transmission?

Otherwise, I would start with the standard check, specifically how the boost pressure regulation is behaving.

No automatic !
The engine noise, driving sounds, and perceived speed are all normal as usual, except the tachometer is showing 1000 RPM too high, and there's no power when accelerating.
The top speed is then only approximately 140 km/h .
And after the "restart," everything is back within the normal range!

"intermittent error"
"occasional error"
"sporadic error"
What is this supposed to be?
Turbocharger boost pressure regulator replaced, wiring harness undamaged?
What now?

R-TDI wrote:

The engine noise, driving sounds, and perceived speed are all normal as usual, except the tachometer shows 1000 RPM too high, and there is no power when accelerating. The top speed is then only approximately 140 km/h . And after the "restart" was performed, everything was back within the normal range!

That's quite something...

Let's assume the EDC (Engine Control Unit) receives a faulty signal indicating 1000 rpm too high due to a crankshaft sensor error. Consequently, it calculates the number of intake strokes per minute based on this incorrect speed, assumes insufficient cylinder filling, and reduces the amount of fuel injected via the soot reduction system.

Wouldn't that fit with the symptoms?

I would then start searching in the area of the OT sensors - although without knowing exactly what I'm looking for .

Quote:

And after the "restart" was performed, everything is back within the normal range!

Or, could the speed input stage of the MSG be faulty and reset by turning it off and on? Unfortunately, I don't know the answer to that.

That's the problem with the 1000 revolutions!
Even changing the regulator didn't help...
The same error keeps appearing! It's also showing up in the error memory, and the workshops don't know what to do either... which, unfortunately, isn't surprising.
I'm just saying my "jerky AXR"....

Hello,
The AHF is a vehicle with a 110 hp engine, but it's not a diesel (PD). I can run it on up to 50% biofuel without any restrictions, although I only use it for long distances. I'm not yet sure how it will perform in the winter.
Based on the last post, it sounds like the system is in emergency mode, but what's causing it?
Perhaps there's a loose connection in the power supply relay? ("Tunesia relay," a known problem with the G4). Could such a brief power interruption potentially affect the instruments?
Sure, here is the translation of the text from German to English:

"Hello"
harald

R-TDI wrote:

That's the problem with the 1000 revolutions! Even changing the regulator didn't help....

LiMa regulator replaced

No wonder it doesn't help: The TDI engine receives the speed information directly from the crankshaft, but not via the alternator!

The problem must be located somewhere within the range of the temperature sensor, the cable, and the control module.

No, it wasn't the Lima regulator, but the boost pressure regulator that was replaced.

Here I am again.

Unfortunately, I'm still having problems with the ALH-TDI.
LMM replaced, vacuum lines checked for leaks, and both pressure regulating valves inspected.
switched to an AGR control system...
VAG-Com still shows the sporadic error in the pressure control circuit.

What is an EDC ???
Someone wrote about it.
Please help, otherwise I'm going to go crazy .

Write again...
Best regards,
Ralf

EDC = Electronic Diesel Control.