ECU always turning on and off

dianiskovamonika_194113
Sun, 13 Jul 2025 20:51:27 +0000
Maintenance/Repairs

Hi, I started learning about cars so I bought no start ford mondeo mk4 with electrical problem. When the wake up signal comes to the ecm, the ecm starts to always turning on and off. Thats why also other components like glow plug relay, actuators… And so on are pulsating. I have tried many things, grounds, can bus(because ecm is not communicating), measured ecm.

My newest discovery is that i tested ecm on my workbench. I connected power supply, grounds, wake up signal (which goes from body control module) and last one of the pins that are pulsating. In this case it was pin from glow plug coil relay(12 volts go through coil and ecm should ground it, but when i measure at ecu with osciloscope. Voltage is pulsating from 0V to about 3V in matter of miliseconds.) So my test results were exactly how ecu acted connected in a car. The relay was pulsating. That is when you would say, oh then the ecm is bad. BUT. I tried other 2 ECMs and the have all acted like this one. The question i have now is, is there something that I have to connect while testing on a workbench that will wake up the ecm like it should be? That would means something in my car is not fully waking up the ecm. Main ignition relay coil and load sides are good, wake up signal from body control module is also good.

I really want to learn about cars so i chose this hard path, but I no longer have options in my head. Thats why I want to ask you more experienced guys.

8 posts - 5 participants