1. Have you got the right chip for your ECU? ie Level1/6/8 chips are not interchangeable, so you must have a chip that is suitable for whatever ECU you have.

2, Is the chip plugged in the right way round? The little notch in the end of the chip should face towards the edge of the circuit board.

3, Is the chip plugged in correctly and securely, with no pins misplaced and hanging out?

4, Is the main ECU connector plugged in securely and locked in position with the retaining clip?