Featured Toyota head unit with amplifier.

Crabber said:

This is my first post, I have joined your forum to get some understanding of car audio. This is a long saga so I will try to be as brief and concise as I can.
I have a Toyota Prado and changed the factory head unit (Fujitsu) for a Chinese (Dasaita) unit as an android unit is so much more capable of running whatever apps you need rather than being limited to what the OEM unit allows.
This has worked really well for several years but would not run apps like Waze as they need a minimum of android 10. I have since flashed updated firmware thanks to XDA forum so the issue has been resolved.
Now to the audio question. I first bought another Chinese head unit which would only drive the front speakers, there was no sound out of the rear in the car via the factory amp.
However testing with small temporary speakers all front and rear speakers worked both directly from the head unit using it's internal amp and via another amp using the outputs with RCA plugs.
I obtained a schematic from Toyota but got very confused as the car does not have rear speaker wiring for both sides just the left side.
So my question is how on earth does the system work? Am I right in thinking that just the left and right channels go to the factory (JBL) amp under the seat and the amplifier separates the front and rear? The head unit that works all channels has what is called an "amp" app and the one that doesn't work the rear speakers has an app called DSP. I don't know if this is relevant but I do know that the canbus settings in the head units have to be correct to get any audio at all.
I have attached a photo of the factory unit sockets.
View attachment 69963

Click to expand...

It sounds like you're dealing with a complex audio system setup in your Toyota Prado. Let’s break down your questions:

1. **Audio System Architecture**: In many vehicles with factory-installed amplifiers (like your JBL system), the head unit typically sends a low-level signal (like RCA outputs) to the amp, which then controls the speakers. If your factory amp is designed to split signals between front and rear speakers, it usually requires a proper input from the head unit to function correctly.

2. **Wiring Confusion**: The lack of rear speaker wiring on both sides could indicate that the factory amp is using a signal mix from the head unit. It’s possible that the amp is receiving a stereo signal and internally routing it to the appropriate speakers. This is why you might be hearing sound from the front but not the rear with certain head units.

3. **Head Unit Compatibility**: The difference in performance with your two head units (one working with all channels and the other not) may stem from how they handle audio outputs. The “amp” app likely processes audio differently than the “DSP” app. Make sure your canbus settings are configured accurately to ensure the amp receives the correct signals.

4. **Troubleshooting Steps**:
- Check the settings on your new head unit to ensure it is outputting the correct audio signals for a system with an external amplifier.
- Ensure that the wiring harness is correctly connected to the factory amp.
- If possible, consult the wiring diagram from the Toyota schematic to verify the correct pinouts for your vehicle’s amplifier.

5. **Next Steps**: If you continue to have issues:
- Consider reaching out to forums specific to Toyota audio systems, as other users may have experienced similar challenges.
- If you’re comfortable with wiring, you might consider testing individual outputs to verify functionality.

If you have specific wiring diagrams or additional details, they could help narrow down the issue further.