The tank pressure sensor is usually in the top of the fuel pump assembly. BUT pressure warnings can be anything from a cracked rubber line or rusted fill pipe or bad gas cap seals. You need to do a complete EVAP system integrity check.

Here is a generic EVAP system diagram, showing most of the parts and valves.

Here's a DTC site that gives some troubleshooting and repair advice for each code found -

OBDII diagnostics. Trouble codes description for GM

OBDII diagnostics. Trouble codes description for GM

obdii.pro

 

I swapped out my evap solenoid under hood, cuz it was ticking loud, got no codes, was simple and only 25 bucks from Bosch...

 

smoke tester may be a option from a mechanic? you can buy one on amazon.de, but its silly to spend 300 euro on a tool you only use once?

Ein Rauchtester von einem Mechaniker wäre vielleicht eine Option? Sie können einen bei amazon.de kaufen, aber es ist dumm, 300 Euro für ein Werkzeug auszugeben, das Sie nur einmal verwenden?

 

P0451 – EVAP Pressure Sensor Range/Performance

The fuel tank pressure (FTP) sensor is reporting values outside of what the PCM expects. This can be due to wiring, sensor failure, or an EVAP system issue.

P0453 – EVAP Pressure Sensor High Input

The PCM is seeing a consistently high voltage from the FTP sensor (often >4.5V), which usually indicates a short to voltage, faulty sensor, or wiring issue.

Common causes on the STS 3.6:

1. Faulty fuel tank pressure (FTP) sensor – this is mounted on top of the fuel tank (part of the EVAP system).
2. Wiring/connector issues – damaged or corroded wiring to the FTP sensor.
3. PCM reference/ground issue – less common, but worth checking if both codes appear together.
4. Rarely: actual fuel tank/charcoal canister pressure problem – but usually it’s electrical

How to diagnose:

1. Check live data with a scan tool – look at FTP sensor readings (should be around 1.5V with key on, engine off, and fluctuate slightly with tank pressure changes).
2. Inspect wiring and connector at the FTP sensor – look for corrosion, broken wires, or a loose fit.
3. Backprobe the sensor – verify 5V reference, ground, and signal return voltages.
4. If wiring is good and voltages check out, the sensor itself is the most likely failure point

Fix:

• Replace the fuel tank pressure sensor if it’s out of range or stuck high.
• Clear codes and retest.

 

I assume, tank of a CTS is da same?

 

Problem solved, defective fuel tank pressure sensor replaced, thanks for all the comments.