Generator Ground Same as Body Ground?

Hello,
I have a big problem: 5 error messages.

Intake air temperature: open or shorted to B+.
Diesel temperature: open circuit or short circuit to B+.
Coolant temperature: open circuit or short circuit to B+.
Accelerator pedal sensor: implausible signal.
Brake light switch monitoring.
The engine has an idle speed that is too high, approximately 1200 RPM.

The Gaspoti display shows the 0-100% readings correctly. The intake air temperature shows approximately 8 degrees Celsius, while the diesel and water temperatures show approximately -6 degrees Celsius (which is already incorrect!).
"When I press the brake and clutch pedals simultaneously, all three sensors show readings below -20 degrees."
As far as I can tell, the three sensors – the throttle position sensor, the clutch switch, and the brake switch – along with some other components, are connected to the same ground point on pin 33 of the control unit.
"Shouldn't the potential be the same as the battery's negative terminal? I can only explain this with a ground fault. And according to my multimeter, there's about 10 megaohms of resistance between the sensor's ground and the battery's negative terminal."
I've successfully measured continuity between the individual components (donors and switches), but not yet to the control unit (STG).

Hello,
In 'older' vehicles, a grounding connection can sometimes corrode and become 'high resistance.'
'As a test, try connecting a separate ground wire from the temperature sensors to the battery ground.'
The error should be gone then.
Best regards,
Günther.

Should the potential not be identical to the battery negative terminal?

It should. However, the sensor and actuator mass are physically separated by the control unit. On the sensor side, it is important to design the grounding paths in as star-like a configuration as possible (to avoid ground loops).
The actor side is usually equipped with power drivers that need to be as well-isolated as possible from the rest of the system (especially due to the use of switching power supplies for things like PD), hence the separate ground plane.

Check your wiring harness for any breaks and inspect ALL (connector) connections for corrosion.

CU.

Okay, here I am again. This is really getting on my nerves, people.
"I'm getting 100% continuity between each of the power supply terminals/switches on this main wire, and also to pin 33 on the control unit. I suspect a trace or something similar has failed. I haven't felt like opening it up to investigate yet. Just for fun, I stripped back and soldered together the brown and brown-blue wires on the MAF sensor connector, and everything is working again."

Hello snowman,
It appears that one of the two main power lines is broken (in the control unit), and the other is now 'taking over.'
Best regards,
Günther.

Schneemann wrote:

Once, just for fun, I stripped a small section of the brown and brown-blue wires from the LMM connector, soldered them together, and everything worked fine again.

Well, it's not ideal, though (see rinderwahnsinn's notes on normal weight management).

If there's actually a blown ground path in the engine control unit, there's a reason for it. I would definitely investigate that further.