Help diagnose Misfires, P2152 Supply Voltage for Fuel Injector Group C


I’m stuck diagnosing a misfire on my RS4. I have major misfires in cylinders 5 & 6, and have fault code P2152 Supply Voltage for Fuel Injector Group C. I’ve been searching for threads with similar issues and all I can find our people having misfires due to a failing 614/644 relay. I’m fairly certain (but not positive) that is not my issue since my misfires are very specific to a particular circuit and not happening in any other cylinders. Also car starts up just fine. There are really no other symptoms. Only other problem I have ever had was the car going into limp mode after going through a car wash, and research suggested that was because water got into the ECU box.

Most of what I have found in search of an answer says I likely have a bad wire connection but I don’t know where to look. I can’t find a diagram or better yet just pictures of the fuel injectors circuit and those running the Group C injectors. Could someone point me to something that could direct me exactly where I should look? Is there a fuse for the different injector groups? I was hoping it would be an easy fix like a fuse. Do I have to take the manifold off to look at all places there might be a short?

Any help is much appreciated. Thanks

Is the code your getting something that pops back up right after you clear codes. Or do you need to drive the car for a while. Generally wire breaks or shorts trip a code that you can’t clear.

The ECUs are quite open and not in a box like the older cars they are just under the rain tray. So you might want to start with that.

Pulling the intake wouldn’t be a bad idea. If you remove the intake you can do a deeper inspection to try and get a hold on whats going on.

Code always reappears after clearing. Used VAG to scan voltage and cylinder 6 was at 0 and 5 was nearly 0. Cylinders 5/6 are right front of engine so I’m not sure how removing air box will help. Point is I don’t know how to trace the circuit/wires from the injectors back to where they originated without a diagram. If the short is not at the connection with the injectors, under the manifold, then maybe I can find it without having to pull things apart.

Does anyone have a wire diagram of the engine?

PM me your email and I can send you pictures of the wiring diagram.

It looks like the fuel injector wiring goes from the injectors, thru a 14 pin black connector inside the ECU box, and then straight to the ECU #2. I am willing to bet when you went thru the car wash that water got into the ECU box and got on 14 pin black connector along with some of the other connectors. Make sure that you have all five screws in the ECU box and that it is sealed correctly after checking each connector. I would open the ECU box, pull each connector on the back of the inside of the box apart, and spray them with electrical contact cleaner just to eliminate that as a possibility.

The pins are labeled on each connector somewhere usually in really small numbers but here are the assignments.
The 14 pin black connector inside the ECU box.
Cylinder 5 - Pin 1 is power and 2 is ground
Cylinder 6 - Pin 3 is power and 4 is ground

At the 60 pin ECU #2 connector.
Cylinder 5 - Pin 33 is power and 2 is ground
Cylinder 6 - Pin 48 is power and 16 is ground

At each injector.
Pin 1 is power and 2 is ground for both injectors.

Justin meant to pull the intake manifold not the air box by the way. To check the connectors at the fuel injectors themselves.

Rgr. Thanks for the guidance. This is very helpful. Hopefully it will be easy and I don’t have to pull the manifold.

Update: I gave up and went to Indy shop for help. Indy shop said wire testing showed no shorts or cut in the circuit and thinks that the ECM has a fried injector driver. In all my research of this platform I never heard of ECU’s going bad. Anyone had a similar situation? Hoping someone has seen a similar diagnosis but then realized it was actually something less bad like a bad relay (which my tech checked). I think he knows what he is doing.

The only similar thread I’ve recently found was a guy who was told by a dealer he had two replace both ECMs, even though only one was bad, and that it would be $4800. I can’t go down a similar path.

Update: I had my ECM (slave) tested and all injector drivers are working properly. Also, if my mechanic was correct that there is not a wiring problem, does anyone have any ideas where else I might look? Could the infamous relays (411/644) be the problem? We did try swapping them to see if the problem would move around and it did not.

Again, only faults were misfires on 5&6 and the code for the supply voltage for group C injectors. Also, the manifold has been pulled so the wires to those injectors were inspected thoroughly.

Help. Out of ideas.

move the injectors to the other side of the motor and see if the code follows them. You could just have two bad injectors that fault out.

I would also just replace the relays with new ones as they are not that expensive.