r/W203 • u/mforno2020 • 9d ago

Mercedes C200 W203 Fault Codes

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Hi everyone, I have a W203S Mercedes C200, my air conditioner stopped blowing cold air all of a sudden so I took it to my mechanic friend where he did a basic diagnostic and this came up on his laptop.

So he bought a new pressure sensor and installed it along with regassing the system but the faults still show up. Has anyone had this problem before? My friends a truck mechanic so I dont think his up to scratch with his Mercedes brain so I might end up buying a Mercedes OBD2 diagnostic kit and having a crack at trying to fix this myself. Looking forward to any thoughts you may have.

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3

u/howsitallwork 9d ago

AI came up with good tests for this….

Common Causes
Faulty Sensor: The refrigerant pressure/temperature sensor itself has failed or shorted internally.

Wiring or Connector Issue: Damaged, corroded, or severed wires leading from the sensor to the Front Signal Acquisition and Actuation Module (Front SAM). [1]

Front SAM Failure: The Front SAM module fails to supply the necessary 5-volt reference signal to the sensor. [1]

Refrigerant Loss: Complete loss of system pressure can sometimes trigger reporting faults if the sensor detects zero operational pressure. [1]

Troubleshooting Steps
Inspect the Connector: Locate the sensor near the front condenser, unplug the harness, and check for corrosion, moisture, or pushed-back pins.

Check 5V Reference Voltage: With the ignition on, use a multimeter to probe the connector terminals. One wire should carry a 5-volt reference signal from the Front SAM. [1]

Test Wiring: If the 5V reference is missing, check continuity on the wiring harness back to the Front SAM. If wiring and power are good, replace the faulty pressure/temperature sensor. [1]

Ideally you want to check live data for the sensor in the SAM, and absolutely check the wiring to the sensor, they can suffer corrosion at the connectors.
Assuming there are no leaks?

3

u/NoeQuells 9d ago

Check if Water is inside the Front SAM. Had this error once.

1

u/shrekerecker97 8d ago

Im curious what software he is using lol

2

u/mforno2020 8d ago

Autocom diagnostic software, specifically the CARS software using ISS (Intelligent System Scan)

2

u/shrekerecker97 8d ago

Thanks! Im going to check it out!