Model: Discovery 4, V6 diesel engine 3.0L.

VIN: SALMN15486A××××××.

Driving mileage: 33418 miles.

Issue: The customer reported that the sunroof of the car could not be opened.

 Diagnosis: The car was brought into the factory for routine repair. The sunroof could not be opened, according to the owner. The sunroof did not respond when the sunroof switch was operated after the vehicle key was switched on, according to the fault verification. The sunroof calibration with Land Rover's unique diagnostic device yields no results.

 When connecting the diagnostic instrument to read the fault code, no associated fault code is found. The following are the main reasons for the fault, according to the analysis of the fault phenomenon:

1. The sunroof motor is damaged or the sunroof mechanical failure.
2. The sunroof module is damaged.
3. The sunroof operation switch is damaged or related wiring reasons.

 It is relatively simple for a given electrical component of the car to fail to be regulated. Mechanical jams induced by long-term usage of the originals, or fuse blowing due to jams, are the most common causes of problems. So, based on past experience, remove the glove box from the front passenger's seat (where the fuse box is located in the car), check that the necessary fuse is not blown, and use a multimeter to measure 12.21V. (when the key is turned on). It appears that the problem is more complicated than that. After examining the pertinent data and we found that the sunroof switch (together with the ceiling light), sunroof motor, and independent sunroof module all regulate the car's sunroof, while the power supply is supplied by the body power box.

 After receiving the sunroof switch signal, the sunroof module operates the sunroof motor directly, according to the circuit diagram. The car's sunroof module is located in the middle of the roof, above the front seat's headrest, thus the sunroof module is removed, and the two power sources supplied by the passenger fuse box are examined for voltages more than 12V. Check that the ground wire and grounding point of the module are both 0.01Ω; the power supply and grounding of the sunroof module appear to be in good working order.

 Between the switch and the module, there are three wires connected: one is the green and black SWITCH GND switch grounding, one is the green open signal, and the other is the orange close signal line. Disconnect the switch plug at the module to measure with a multimeter. The green wire is connected to the green and black SWITCH GND wire when it is pressed to open, and the orange wire is connected to the green and black SWITCH GND wire when it is pressed to close. The sunroof switch appears to be in good working order and may be ruled out.

This sunroof motor is a stepping motor connected by 6 wires, 4 wires are the position signal wires, and the other 2 wires are the power supply for driving the motor (the wire diameter is thicker). Connect the plug and connect it to the multimeter for measurement. When there is no voltage display (normally it should be positive and negative power supply voltage). The sunroof motor works after the plug is disconnected and the power is directly supplied, thus eliminating the sunroof motor and the mechanical failure of the sunroof.

 Troubleshooting: Replace the sunroof module, perform module configuration and sunroof calibration.

 Summary: The control module on the vehicle is relatively stable, and there must be

conclusive evidence to prove it when there is no fault code prompt. The fault does not seem complicated, but it is not easy to understand thoroughly.