brooksie
New Member
Hi all, Thanks for allowing me in and I hope you guys can help...
My problem started when the intercooler hose split, up until then the car worked fine, power was good, kickdown worked, the engine ran well and performed as expected.
Once the hose split, the engine management light came on, and the car ran in limp mode.
I had trouble getting a replacement hose, so for a while the car ran in limp with a temporary repair to the hose.
As the engine was not being pushed, I think the DPF filter became clogged causing secondary problems.
The hose was replaced, fault code reset, the engine light out but the performance was low with no kickdown.
The MAF sensor was blamed, and replaced with another, not new one, and eng mgmt. reset. Still poor performance.
The DPF showed signs of being clogged on the diagnostics, so was cleaned and a regen run. Still poor performance, but eng mgmt. light out.DPF readings now acceptable.
After some while, the eng mgmt. light returned, and the fault pointed to MAF sensor. A pattern Ridex sensor was sourced and fitted, eng light reset. Still poor performance, and after a while the light was back on.
Time to dig deeper. With the engine running, voltages on the MAF sensor were checked.
12V-OK, Gnd-OK, Output-around 1.2v to 1.5v, 5V Reference voltage-low @2.5v.
Mercedes cct diagram for ECU obtained, and established the source of the 5v, this comes from the ECU internally.
The schematic diagram of the ECU does not show the internal components, only the internal block diagram.
When the MAF sensor is unplugged, the 5V returns to 5V as if there is a load on the 5v output supply,(measured on the ECU output side) but drops when the plug is refitted, engine on or off. As the MAF has been replaced, this now points to the internal voltage regulator in the ECU being faulty.
The garage that has been investigating for me advised that maybe Mercedes should look into this, so as the car had to go in for an Airbag replacement, I asked them to reset the system at the same time which they did FOC. After the 10 mile drive home, and a restart, on came the light again. They did not look any deeper into the problem as they thought the software update they carried out and the airbag reset may have fixed it, although the power was low still with no kickdown when I picked the car up.
I now believe the problem lies within the ECU, but understand this is probably very costly and may not be the fix.
So, I need to understand what the MAF Reference voltage is on a working car, is the 5v marked as 5V but in real life is it different?
How comes my 5V is low..is this normal?
Has anyone had this problem and what was their fix?
Any help/ideas very much appreciated...
My problem started when the intercooler hose split, up until then the car worked fine, power was good, kickdown worked, the engine ran well and performed as expected.
Once the hose split, the engine management light came on, and the car ran in limp mode.
I had trouble getting a replacement hose, so for a while the car ran in limp with a temporary repair to the hose.
As the engine was not being pushed, I think the DPF filter became clogged causing secondary problems.
The hose was replaced, fault code reset, the engine light out but the performance was low with no kickdown.
The MAF sensor was blamed, and replaced with another, not new one, and eng mgmt. reset. Still poor performance.
The DPF showed signs of being clogged on the diagnostics, so was cleaned and a regen run. Still poor performance, but eng mgmt. light out.DPF readings now acceptable.
After some while, the eng mgmt. light returned, and the fault pointed to MAF sensor. A pattern Ridex sensor was sourced and fitted, eng light reset. Still poor performance, and after a while the light was back on.
Time to dig deeper. With the engine running, voltages on the MAF sensor were checked.
12V-OK, Gnd-OK, Output-around 1.2v to 1.5v, 5V Reference voltage-low @2.5v.
Mercedes cct diagram for ECU obtained, and established the source of the 5v, this comes from the ECU internally.
The schematic diagram of the ECU does not show the internal components, only the internal block diagram.
When the MAF sensor is unplugged, the 5V returns to 5V as if there is a load on the 5v output supply,(measured on the ECU output side) but drops when the plug is refitted, engine on or off. As the MAF has been replaced, this now points to the internal voltage regulator in the ECU being faulty.
The garage that has been investigating for me advised that maybe Mercedes should look into this, so as the car had to go in for an Airbag replacement, I asked them to reset the system at the same time which they did FOC. After the 10 mile drive home, and a restart, on came the light again. They did not look any deeper into the problem as they thought the software update they carried out and the airbag reset may have fixed it, although the power was low still with no kickdown when I picked the car up.
I now believe the problem lies within the ECU, but understand this is probably very costly and may not be the fix.
So, I need to understand what the MAF Reference voltage is on a working car, is the 5v marked as 5V but in real life is it different?
How comes my 5V is low..is this normal?
Has anyone had this problem and what was their fix?
Any help/ideas very much appreciated...
