2010 Kia Rio ECU "C" keeps blowing

WLHarrisjr

Losing what is left of my mind. Trying to help a friend out with his car. initial issue was one second run, the n shut off. Now, the ECU-C fuse is blowing as soon as the kety is turned on. As far as I can tell that means a main relay or AT circuit failure, but I cannot find any issues with either system. Shipped the ECU off for testing and came back as fine. Any advice from those more familiar with Kia than I?

Bill

thecardoc3

Fuse C provides power to the PCM (engine control module) on pins 4,5 and 6 of Connector #1. These power inputs become power outputs from the PCM. The first thing you need to determine is if the problem is before, or after the engine control module. The Grey wire from fuse C goes to the engine room relay box where internal splices in the box feed the computer inputs. This is done via connector JC/12.

The routine I would employ knowing how the circuit breaks down would be to make jumper leads and install a headlight in place of fuse C. This will allow the circuit to be partially powered up while restricting the current in the circuit. I would use an inductive current probe that clamps around the wire to measure the current flowing in the circuits. The one with the highest current would be the suspect circuit. Keep in mind the failure could be before or after the PCM. If it is before the PCM, the current probe would lead right to the failure by accessing different points along the path towards the PCM. If it is after the PCM the routine would continue by opening the circuit with the highest current. Then install a new fuse and start checking to see which PCM outputs are missing power. The next step would be to open those circuits. try to power them up with the headlight and repeat the process with the current probe on just those circuits.

The wires at J/C12 that are the affected circuit are highlighted in the red ovals. The left side is the out to the PCM.