13.4 instead of 14.2 volts

Hi.
I'm currently looking at a Volkswagen Golf 3, and I'm quite puzzled.
While the engine was running, I measured 14.2 volts across the terminals.
The voltage readings for both the positive terminal (Lima Plus) and the ground connection are 14.2 volts.

and VCDS shows me 13.2 volts as the battery voltage in the advanced measurement values.
Recently, the driver experienced the following effect.
This morning, the car wouldn't start, but the temperature displayed on the dashboard showed 90 degrees.
After much struggling, the car finally started, but it stalled again after a short time while driving.
After that, it ran as usual, and the temperature was displayed correctly again.
The vehicle has a 1.4-liter AEX engine with 60 horsepower and was manufactured in [Year]. September 1997.
After checking the wiring externally and finding nothing, I suspect there might be a cold solder joint inside the control unit.
Is it worth investigating this further, or is there a simple explanation for the missing voltage?
Sure, here's the translation:

'PS: Mass connection is okay.'
Best regards, Frank.

Hello,

In which control unit were the 13.2V measured? Possibly compare voltage values in different control units at some point.
If measurements were taken in the engine control unit (ECU) and it's being powered by a (partially defective) relay, I could explain the observed effects.

Best regards, Rainer.

Evening.
I would have immediately thought of relay 109 as well. It will certainly have a different name for the gasoline version, but it will cause the same problem in the long run.

Best regards,

Hi Frank,
We also used to have the AEX (and also experienced that startup problem).
The cause was the temperature sensor. He initially showed sporadic signs of increased...
Temperature (leading to reluctance to start) and, after a relatively short time, to...
Approximately 100°C sustained temperature (no more surging).
After replacing the sensor, the problem was resolved.
Temporary solution: Unplug the device until the motor warms up.
Unfortunately, I cannot confirm whether the engine control unit displayed a voltage that was too low.
I can't say anymore.

Best regards,
Micha

Hello,

In which control unit were the 13.2V measured? Possibly compare voltage values in different control units at some point.
If measurements were taken in the engine control unit (ECU) and it's being powered by a (partially defective) relay, I could explain the observed effects.

Best regards, Rainer

In the extended measurement data above, the first value represents the battery voltage.
I'll check now to see if I can connect to the control unit.
I think it should be MSG.
'How do I find this relay, and what is its name?' Number?
Best regards.

For the diesel engines, it was the infamous relay 109.
It could be in slot 3 and have the number 30 or 288.
(if applicable).

Unfortunately, it's a gasoline engine.
I'll take a closer look at the cables again tomorrow, when I have more time.
I found 0.3 volts between the engine block and the body.
So, the ground cable must be faulty.
Best regards, Frank.

I checked all the ground cables, cleaned them, and did everything else I could find that might be relevant.
According to VCDS, the control unit is not receiving enough voltage.
It's running smoothly again without any errors, and the owner has now sold the car.
The solution isn't pretty, but at least the problem is gone.

I replaced the temperature sensor as a precaution.


Best regards, Frank.

"In the 'Relais 109 problem,' the connectors and contacts soldered into the main circuit board had faulty solder joints, which of course is only visible if you remove the casing."

Hi Rainer,
Does the AEX engine, when running on gasoline, have a relay number 109?

Best regards, Frank.

The AEX typically uses a relay with a rating of 30.