7 basic steps – how to check if the ECU is working.
1) Check that the ECU has power externally at the plug.
- Check the GND of the device.
- Check the constant power supply (+30)
- Check the power supply after the ignition (+15)
2) Find inside the ECU device, electrolytic capacitors and measure the power supply voltage on them. Inside the ECU device, there may be a voltage of 5V or 3.3V around the microcontroller.
3) Find the pdf documentation for the microcontroller and determine on which pin is the reset signal. Then check if this reset signal has the right state. If it has an inappropriate state or is cycled, it could mean that the microcontroller is being reset by an external Watch-Dog circuit.
This could be related to an electrical fault in the ECU or a software fault.
4) If you have the opportunity, read the program code and compare it with another program – to check whether the contents of the program memory (Flash or eeprom, etc.) are corrupted.
5) Check if the microcontroller’s generator clocks its clock. Do the measurement with an oscilloscope on the generator or quartz.
6) Check if signals are being sent to the CAN bus. Find a circuit to handle the CAN bus, they are often 8-leg integrated circuits, and next to them there is a filter (similar in appearance to a 4-leg optocoupler). With an oscilloscope, see what signals are on the CAN bus.
7) In the documentation, see on which pins of the microcontroller are I2C, SPI and parallel bus signals. See with an oscilloscope if the signals are there.
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