Fuel Pump pinout
Thread Starter
Newbie
Joined: Jun 2025
Posts: 3
Likes: 1
2004 E500 Wagon
Fuel Pump pinout
Updated information:
Thanks in advance.
Previous Notes:
I just replaced my fuel pump (Hella) and fuel sending unit (Hella) with the mercedes oem adapter that changes the 3 pin squarish connector to the 3 pin oval connector.
Got P0446 repeatedly (tried clearing it but it returned).
Connected scan tool and found that the fuel tank pressure is reading -30 hPA when the engine was off.
Opened the gas cap and the pressure reading did not change.
I would expect a reading near 0 hPA (to indicate normalized pressure).
I'm guessing that the adapter wired are swapped (surprising since I did not splice any wires, just connected the adapter to the new Hella fuel sender).
Is a reading of -30 hPA when the engine is off and gas cap removed correct?
Does anyone have the correct wire color or pinout for the fuel pressure sensor connector?
- Tested purge value both on bench and using DAS; works fine.
- Testing vent valve using DAS; I could hear the solenoid click. Also tried closing it with the engine running and could see the fuel tank pressure PID change so I know the vent value is working
- With the Engine off and gas cap open, the Fuel Tank Pressure Difference ADC (617) shows 1.52V and Fuel Tank pressure Difference (017) shows -30 hPA.
- Car will throw a P0446 CEL if the vent open pressure reading is not near atmosphere
- Why is the FTPS reading -30 hPA? I tried removing it from the sending unit so its exposed but the value did not change.
- Does anyone know what the voltage reading should be for a W211 FTPS with the engine off and fuel cap open?
- When closing the vent valve and starting the engine, the FTPS reading went from -30 hPA to positive 20 hPA.
- This seems counter-intuitive. Shouldn't the pressure reading drop since fuel is being used without any vent air?
- If I opened the vent valve, the pressure reading returns to -30 hPA and stays there.
- I checked youtube videos and my wire colors seems to be in the right location (genuine MB adapter)
- Since the pressure change seems backwards, I switched the positive and ground on the adapter. The engine off, fuel cap open showed 40 hPA so that wasn't correct.
- Based on the thread https://mbworld.org/forums/c32-amg-c...cuum-leak.html, I tried swapping the signal and ground but that didn't work either.
- My signal is changing when the vent is closed and engine is on so it appears that my signal wire is working (but the pressure difference value is increasing according to DAS).
- I tested the voltage from the ECU connector when disconnected from the pressure sensor. Its 5V from positive and 4.7V from signal (in case it helps with diagnosis).
- Does anyone know what the FTPS voltage reading should be for a W211 FTPS with the engine off and fuel cap open?
- Shouldn't the pressure reading difference drop (e.g. 0 hPA to negative hPA) when engine is on and vent valve is closed?
- Is there some kind of reset or adaptation when changing the FTPS?
Thanks in advance.
Previous Notes:
I just replaced my fuel pump (Hella) and fuel sending unit (Hella) with the mercedes oem adapter that changes the 3 pin squarish connector to the 3 pin oval connector.
Got P0446 repeatedly (tried clearing it but it returned).
Connected scan tool and found that the fuel tank pressure is reading -30 hPA when the engine was off.
Opened the gas cap and the pressure reading did not change.
I would expect a reading near 0 hPA (to indicate normalized pressure).
I'm guessing that the adapter wired are swapped (surprising since I did not splice any wires, just connected the adapter to the new Hella fuel sender).
Is a reading of -30 hPA when the engine is off and gas cap removed correct?
Does anyone have the correct wire color or pinout for the fuel pressure sensor connector?
Last edited by salty72; Jul 2, 2025 at 10:17 AM. Reason: Added new information.
Thread Starter
Newbie
Joined: Jun 2025
Posts: 3
Likes: 1
2004 E500 Wagon
Update for future reference (in case others are looking for the same information):
Fuel Tank Pressure sensor seems to increment 1 hPA per 0.05V.
A good atmosphere signal is 3V (0 hPA).
A value of 5V corresponds to 40 hPA.
A value of 1.5V corresponds to -30 hPA.
[My sensor was defective; fixed with a replacement.]
Fuel Tank Pressure sensor seems to increment 1 hPA per 0.05V.
A good atmosphere signal is 3V (0 hPA).
A value of 5V corresponds to 40 hPA.
A value of 1.5V corresponds to -30 hPA.
[My sensor was defective; fixed with a replacement.]
