C55 MAF sensor wiring/ecu issues
Thread Starter
Newbie
Joined: May 2025
Posts: 3
Likes: 1
From: Devon, UK
'04 C55 AMG estate
C55 MAF sensor wiring/ecu issues
Hi all,
I have just picked up a 2004 C55 AMG, all is well except the engine is idling very rough and sometimes stalls when warming up. I scanned the car with an Autel scanner and found that I have the fault code P2004-4, relating to the MAF sensor signal wiring being at fault, and it also mentions P0104, which I understand to mean essentially the same thing. The MAF was replaced by a Mercedes dealership a few months ago in an attempt to resolve the issue but it still remains.
We have checked the wiring going to the MAF and found these readings:
- Pin 1 - 5v - 1 ohm
- Pin 2 - 12v/battery voltage - 1 ohm
- Pin 3 - 0v - 1 ohm - grounding through the ECU I believe.
- Pin 4 - 5v - 1 ohm
- Pin 5 - Unsure of voltage but reading 1 ohm of resistance
This is not good according to our testing procedure from HaynesPro data, as pin 4 should be at 0v - again grounding through the ECU like pin 3. We checked the pin on the ECU that is connected to the wire for pin 4 and found that it was 5v. This would suggest that the ECU is at fault and that the wiring is okay. We also checked that none of the wires are shorting causing power to be sent up the wrong wires and all is okay there.
Could anyone please verify that pin 4 should definitely be at 0v and that the ECU is at fault here? I really would like to avoid paying out to have the ECU fixed if it doesn't need to be.
Appreciate any help with this
I have just picked up a 2004 C55 AMG, all is well except the engine is idling very rough and sometimes stalls when warming up. I scanned the car with an Autel scanner and found that I have the fault code P2004-4, relating to the MAF sensor signal wiring being at fault, and it also mentions P0104, which I understand to mean essentially the same thing. The MAF was replaced by a Mercedes dealership a few months ago in an attempt to resolve the issue but it still remains.
We have checked the wiring going to the MAF and found these readings:
- Pin 1 - 5v - 1 ohm
- Pin 2 - 12v/battery voltage - 1 ohm
- Pin 3 - 0v - 1 ohm - grounding through the ECU I believe.
- Pin 4 - 5v - 1 ohm
- Pin 5 - Unsure of voltage but reading 1 ohm of resistance
This is not good according to our testing procedure from HaynesPro data, as pin 4 should be at 0v - again grounding through the ECU like pin 3. We checked the pin on the ECU that is connected to the wire for pin 4 and found that it was 5v. This would suggest that the ECU is at fault and that the wiring is okay. We also checked that none of the wires are shorting causing power to be sent up the wrong wires and all is okay there.
Could anyone please verify that pin 4 should definitely be at 0v and that the ECU is at fault here? I really would like to avoid paying out to have the ECU fixed if it doesn't need to be.
Appreciate any help with this
Last edited by then0z; May 12, 2025 at 06:13 PM. Reason: extra info
Thread Starter
Newbie
Joined: May 2025
Posts: 3
Likes: 1
From: Devon, UK
'04 C55 AMG estate
Just to update for anyone suffering the same issue:
I decided to go back to basics and take the throttle body off to clean it whilst I was replacing the valve cover gaskets and breather hoses to ensure that this was not causing the problem. The throttle body was very gunked up, so gave it a proper blasting out with throttle body cleaner. I noticed whilst I had it off that the gasket between the throttle body and the intake manifold was severely deteriorated, so I ordered a new one from Mercedes Exeter. Being sure that this would solve the issue, I started the C55 up to find it was still running very poorly. I then cleared the fault codes and started it again which allowed the ECU to run the engine properly, with the issue being completely solved.
This was one of the most misleading fault codes I have ever come across as it would for sure make you believe that the MAF or wiring was at fault, when in fact it was purely that the throttle body was dirty and that the gasket had deteriorated.
Based off this, the voltage and resistance readings that I issued in my first post are correct (for anyone who may need to look for wiring faults).
Always go back to basics.
Cheers.
I decided to go back to basics and take the throttle body off to clean it whilst I was replacing the valve cover gaskets and breather hoses to ensure that this was not causing the problem. The throttle body was very gunked up, so gave it a proper blasting out with throttle body cleaner. I noticed whilst I had it off that the gasket between the throttle body and the intake manifold was severely deteriorated, so I ordered a new one from Mercedes Exeter. Being sure that this would solve the issue, I started the C55 up to find it was still running very poorly. I then cleared the fault codes and started it again which allowed the ECU to run the engine properly, with the issue being completely solved.
This was one of the most misleading fault codes I have ever come across as it would for sure make you believe that the MAF or wiring was at fault, when in fact it was purely that the throttle body was dirty and that the gasket had deteriorated.
Based off this, the voltage and resistance readings that I issued in my first post are correct (for anyone who may need to look for wiring faults).
Always go back to basics.
Cheers.
