This Issue Guide:
Many mechanics often ask me why the motor won’t start and there’s no response when trying to start the car. When I encounter such issues, I honestly feel reluctant, especially when there are no fault codes. This kind of problem is systemic and involves various aspects of the vehicle, not something that can be clarified with just a few sentences. Both the repair community and drivers usually consider the ECU as a potential cause after checking that the external circuits are normal. Today, I will analyze the issues related to the ECU when there is no response from the car.
No response when trying to start the car usually reports which fault codes?
⊙Actuator 0 Power Short Circuit
⊙Actuator 0 Ground Short Circuit
⊙Starter Relay Power Short Circuit
⊙Starter Relay Ground Short Circuit
⊙Starter Relay Over Temperature
⊙Starter Relay No Load
So, what aspects are related to the no response when starting the car? Based on the fault codes displayed, it is likely related to components associated with the starter relay, so let’s analyze that.
This function has a calibration feature, generally ECUs with this function are controlled by the ECU itself, and some without it can be enabled through calibration, 
The starter relay drive current≦2.2A, common high end K29, control low end pinK71, the start is controlled by the ECU and is mandatory
It controls the starting of the engine, serving as neutral protection, starter protection, and battery protection,
Related components include T15 switch, T50 switch, neutral switch, and starter relay.
Normal ECU simulation testing shows that the starter relay works, and the indicator light is on, proving that the function is intact.
After excluding calibration and peripheral circuit issues through simulation testing, it is determined that the ECU control end issue requires ECU repair.
Next, let’s learn how to repair the ECU together
Controlled directly by pin 53 of chip U10, when operational, the internal switch of K71 connects to ground to form a circuit, allowing the starter to work; when the vehicle does not start, measuring the relay terminals shows 24V voltage.
Here, it differs slightly from EDC7, EDC7 uses dual-end common control, when not starting, measuring both ends of the relay shows 3.5V.
When K71 fails, it reports: starter relay to ground short circuit
Starter relay over temperature
Typically, this is due to the K71 chip burning out, measuring K71 to ground shows a very low resistance or direct short to ground, replacing U10 can resolve this issue.
Which is the control high end issue, causing the common high end to the starter relay power line to burn out, check the burning situation below, check that the control high end chip outputs 24V normally, it’s just that the line is burned out, reconnecting will restore normal operation.
The reported fault code is: starter relay no load
Reports: Actuator 0 Power Short Circuit to ground fault.
Actuator 0 power control is managed by pin 31 of chip U5, outputting 32V voltage to turn on Q8, then outputting 24V common high end power, and monitoring the output voltage through pin 30;
If there is a short circuit to ground or power in the output circuit, it will report actuator 0 power or ground short circuit faults, and the control end will close at 32V; if Q8 fails, it will also report actuator 0 power or ground short circuit faults, closing the 32V control voltage; if Q8 failure is ruled out, replacing U10 will fix the issue.
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Exciting ContinuationUnderstanding the high and low end control principles of the starter relay and the positions of high and low end controls will make it easy to identify where the faults lie. Have you learned it?
