1. Blown Speakers:
- While you mentioned the two front speakers are okay, it is still possible that one or both of them may be blown.
- You can test the speakers by connecting them to another audio source or swapping them with the working rear speakers.
2. Faulty Wiring:
- Check the wiring to the front speakers for any loose connections, breaks, or damage.
- Ensure the speaker wires are properly connected to the correct terminals on the aftermarket stereo.
3. Incorrect Speaker Configuration:
- Make sure the aftermarket stereo is set to the correct speaker configuration. Some stereos have an option to select the number of speakers and their configuration (front, rear, center).
- If the stereo is set to a different configuration, it may not output sound to the front speakers.
4. Output Device Setting:
- Check the output device settings on the aftermarket stereo to ensure it is set to "speakers" rather than an external device like an RCA output or subwoofer output.
5. Power or Grounding Issues:
- Verify that the aftermarket stereo is receiving power. Check the connections to the battery, ground, and ignition wires. Ensure the stereo's ground connection is properly connected to a metal chassis in the car.
6. Incompatible Wiring Harness:
- If you have installed an aftermarket stereo, there might be a wiring harness adapter that connects the stereo to the vehicle's wiring.
- Make sure the wiring harness is compatible with your vehicle and the aftermarket stereo and there are no loose connections or crossed wires.
7. Stereo Faulty:
- If none of the above solutions resolve the issue, the aftermarket stereo itself may be faulty. Try disconnecting and reconnecting the stereo or replace it with another stereo to see if the problem persists.
8. Other Components:
- There may be an issue with other components in the sound system, such as the amplifier, crossover, or head unit. It is recommended to check and test your setup to identify the root cause of the issue.