Engine control unit (ECU) faulty?

My engine control unit seems to be defective. I've experienced limp mode with my TDI on several occasions. In 99% of cases, the error messages in the diagnostic memory indicated "engine control unit intermittently defective" and "charge air pressure control difference." Occasionally, the entry "Donor for intake manifold pressure - short circuit to positive" would also appear.

If the emergency mode occurs, it still works, even now, if you pull over to the right and restart the car. After that, he drives normally again.

Initially, the emergency mode only occurred occasionally when accelerating uphill and then fully accelerating again. However, now the emergency mode is triggered even when the speed is approaching the maximum. The boost pressure is initially only one to two bar at 0.8 bar, but suddenly it drops to 0.1 bar when the accelerator pedal is fully pressed, and then it doesn't increase again. As I said, if you pull over to the right, turn off the car, and then turn it back on, it will go back to normal.

Until yesterday, the error codes could always be cleared without any problems, but now the error code "control unit intermittently defective" remains. However, the "intake manifold pressure control difference" error disappears immediately.

The car is a 1997 TDI with a 110 hp AFN engine. The mass airflow sensor (MAF) and pressure sensor have been replaced. The variable turbocharger (VTG) has already been repaired. The engine control unit (ECU) numbers are: 028 906 021 GH and the Bosch part number is 0281001652. So, if anyone still has a control unit available at a fair price, please feel free to contact me.

Hello,

"I'm usually skeptical when I hear 'control unit defective!' Personally, I've only had one control unit fail so far. In that case, the car wouldn't start. Most of the time, the problem is located elsewhere. But before you do anything else, you should try putting in a new battery temporarily. See also my started thread about a similar problem with a Passat with an AFN engine. Best regards."

Okay, I tested something today. Specifically, the engine is experiencing a problem – it's intermittently failing, even when I briefly rev it up while stationary. This seems to happen around 4000-4500 RPM. While it's not something one should normally do, it needs to be done once for testing purposes.

The "suction pressure differential" error only appears at speeds of 180-190 km/h. The vehicle then immediately switches to emergency mode. The LDA (lateral dynamic assistance) displays a maximum pressure of 0.7-0.8 bar. A bit underwhelming, I think...

Yes, I agree. It definitely can't be the control unit...

I think it might be coming from the charger, but I have to admit that I don't really know much about that.

But surely someone will be able to help.

"Tell me a postal code..."


Maybe someone knows a skilled mechanic?

"The other day, I replaced two boost pressure hoses. One went from the intake manifold to the engine control unit, and it was quite worn out and also porous at the transition between the engine bay and the water tank. The other one was from the pressure sensor to the turbocharger. There was a short section of hose with a protective cover on the turbocharger, as it should be, and the hose from the pressure sensor connected to that short section. I've now replaced them with new hoses that fit directly onto the respective connections." Specifically, the turbocharger looked very makeshift to me.

The maximum speed has been consistently reached since then without any issues. However, I still occasionally experience a sporadic defect with the STG (likely referring to a specific component or system). The error occurs without being noticed.

The postal code is 58239 Schwerte, near Dortmund.

Hello,

The error (SPORADICALLY) - Control unit defect! - could also be caused by oxidized or faulty connectors. Please check all the connectors in the engine compartment, including the large, round central connector.

P.S. What vehicle model do you have that uses the AFN engine?

I have a Volkswagen Golf 3 Variant, first registered in November 1997, with approximately 250,000 kilometers on the odometer.

Okay, I was just traveling at 100 km/h on the train. For the first 70 km, it was fine, even with the maximum speed. After that, I experienced the emergency brake twice, both times at 180 km/h. "Again, the intake manifold pressure control difference and the wastegate are intermittently malfunctioning..."

Hello.

Please check the "ambient pressure sensor" in the control unit, as it measures the normal pressure for the turbocharger pressure regulator. As far as I know, the engine control unit (ECU) uses the normal pressure/ambient pressure to calculate the desired boost pressure for the turbocharger.
"On my old 1z, I had the error message 'Control unit defective,' which was also caused by the 'ambient pressure sensor' located within the control unit."
In my case, it was just a cold solder joint in the control unit, which is why the problem was intermittent.

Best regards,

Do you mean the MAP sensor (Manifold Absolute Pressure sensor), to which the boost hose connects, and which runs from the intake manifold to the control unit (ECU)?

No, he's referring to the small, black box next to it, the one that doesn't have any hoses connected to it.

Best regards, Micha.

"This cylindrical part, which only has two cables connected to it. It's usually attached with a bracket above the control unit, right? But in my case, it's just lying next to the control unit." Perhaps that's where the mistake lies.

I'm not sure which cylindrical part you're referring to.
The ambient pressure sensor is located in the control unit (ECU).

I took a look. What I meant is the sensor for the accelerator pedal position, at least according to the picture. I haven't compared the part number (TN) yet. Is this sensor available separately? STG (Steuergerät) units from the Golf 3 with the AFN engine are really rare.

Apparently, the intake manifold pressure sensor is also available for individual purchase. It's my prime suspect now. Because starting around 180 km/h, I consistently get the "ECU intermittently defective" error, along with the "intake manifold pressure control difference - intermittent" error. About 4 months ago, in addition to those two errors that always appear, I also had a "short circuit to positive" error for the intake manifold pressure sensor, although I had the "control difference" error even before that.

However, that's just my assumption. The car drives normally below 180 km/h, and it accelerates as expected in all situations. Not that you think I'm always turning up the heat, but sometimes things just have to go faster .

It's likely that ambient pressure sensors are available individually, probably in electronics stores. I don't appreciate the way some people act because they would rather replace a "defective" engine control unit (ECU) than repair it.

As far as I know, the error code "STG def" is only written to the error memory when there is an internal problem with the STG (Steuergerät), such as a sensor within the STG.

"Defective intake manifold pressure sensor" also fits the error code associated with the "Def." error. "STG".

Do the readings from the individual sensors match each other, without the motor running?

Best, Chri.

While there are sensors available on the open market, it's not this particular type.
You're most likely to find these in old control units, where something else is used instead.
passed away.

Best regards, Micha.