Hey all,

got a stand-alone CarPlay unit that connects to the aux input of the car. Unfortunately I seem to have a really nasty ground loop. Hugely affected by RPM. If I fit a ground loop isolator between the unit audio out and the car input it gets rid of it but it flattens the sound and reduces the volume.

My understanding is that the aux in and CarPlay power supply (the 12 socket) are grounded at different points which creates the problem.

Is there any (not massively invasive) way of sorting this? I was considering hardwiring the unit into the fuse box as I have done with my dashcam (can’t test it with the dashcam supply as it’s a different connector), so I’ll be running cable etc anyway.

Cheers FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

The use of an inductive load (isolator) in the lead connecting the units only addresses the symptoms.

I have not looked at the feasibility but I suggest that you try directly connecting your power (and earth) to your standalone unit to a fuse point in the same fuse-box as the car entertainment unit.

If the new power connection is a long run then consider a sheathed power cable (or twisted pair), although I think that the interference is from other loads on the local 12v system.

It may however be that your CarPlay unit is picking up the RPM Related Hum by induction from elsewhere and moving it or putting it in an earthed screening box may be necessary.

PS I found this good explanation on line.
https://www.sct.com.tw/articles/4-effectiv...fferences.

Be aware that any in-line filter will change the quality of audio, although it depends on the internal design, will attenuate and change the phase of certain frequencies.

It is best to cure the earth/connection problem rather than mask it. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Thanks, that was really useful. The isolator has certainly dampened the audio, that’s the only way I can describe it.

Question is, where do I try and ground the power supply of the CarPlay unit (I’m assuming that’s where the issue lies - it’s the one creating the audio signal fed into the car and also powered by the car).

So, is it the earth point of the aux input that needs to be the same as the power of the CarPlay unit, or the earth of the head unit? FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

From what I can see The Aux In feeds to the Integrated Audio Module with a twisted pair (L+R) and its own signal earth.
Does your connecting lead compatible and contain a signal earth? Quite small variations across (separate) signal earths can give a lot of interference. Earth can take the form of a 'shielded' cable and/or an internal wire.

The Integrated Audio Unit has an Power(?) earth point to FL2 chassis at G2D114-1.

Click image to enlarge

Click image to enlarge

That is amazingly helpful. Thank you. FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

A couple of general points I have thought of;

The earth connection G2D-114 is under the carpets in the front footwell, and the wiring there has been known to be damaged by fidgeting feet.

I have taken it that there is no interference when engine/alternator are not running, if there is then you may have to look elsewhere. (Including the CarPlay Unit)

Take it step by step, and recheck as you progress, it is easy to get lost when trying to find the source of interference. It may not be easy.

Good Luck. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Interesting! I’ll look under the carpet when I get home. It’s 10 years old, chances are it’s corroded or something.

I plugged my iPhone into the aux in with a different power supply and aux cable and it’s just as bad. As soon as I unplug the power to the phone it’s perfect. So it isn’t isolated to the CarPlay unit, seems to be anything being powered by the car and run into the aux.

It’s very very quiet when the engine is idling but as soon as you rev it it sounds like there’s a little microphone on the gearbox or something. FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

Thanks for investigating further. It would seem that we need to find a common power and earth for both units, as you seem to rule out electromagnet interference.

Do you know if your external connecting cable has an earth running through it to join both units? If I was being faced with this in my old job I would be looking at electrically bonding the cases of both units together as a start.

This Diagram is a better showing of which fuse feeds which module.

Click image to enlarge

Click image to enlarge

So a little update with more detail. I set the CarPlay unit up as normal, but instead of plugging the unit into the aux port, I plugged a set of headphones in and there was no noise/interference at all. So the unit itself isn’t making the noise, it’s only when it is looped into the aux. Which I *think* confirms the whole ground loop thing. FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

A further update. With the unit plugged into the power socket and running, I am getting DAB interference when I try and listen to the radio. Unplug the power and the signal is perfect.

Might I have a noisy power supply as well? Just to confuse things 😂 FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

As the interference is altered by RPM, then I think that it is possibly an AC ripple is getting through to the DC supply. If it is then I doubt if any in-line filter will be sufficient.

The alternator generates AC (at various Engine RPM related frequencies) and this is rectified and smoothed to become 12v DC.

You need to get your Alternator, Diodes, and Regulator checked.

Page 1843 of the Repair Manual says

A single self-exciting generator is located at the front of the engine on the Left-Hand (LH) side of the cylinder block. Two generators are available for the TD4 engine, dependent on vehicle specification. The generators are rated at 90/150 amps and 115/180 amps respectively. The larger rated generator is used on cold climate market vehicles installed with a heated front windshield and electric booster heater.

The generator pulley incorporates a one-way clutch that reduces Noise, Vibration and Harshness (NVH), and improves the life of the accessory drive belt. The one-way clutch allows the belt to drive the pulley without slip occurring, but prevents the generator from driving the belt during transients in engine speed ('belt whip') due to the high rotational inertia of the generator internal components.

The generator comprises the following major components:
Stator
Rotor
Rectifier pack
Regulator.

The stator consists of a flat core pack into which the stator wires are pressed.

The rotor comprises a field winding, wound around an iron core and mounted on a shaft. The rotor is housed within the stator and mounted on bearings to provide smooth running and support, due to the side loading applied by the drive belt tension.

The rectifier comprises 6 semi-conductor diodes mounted on a heat sink. The heat sink dissipates the resultant heat created in the electrical conversion process. The rectifier converts the Alternating Current (AC) produced in the stator coils into Direct Current (DC) that is required by the vehicle electrical system.

The regulator provides a controlled variable voltage output from the generator. Two electrical terminals are provided on the outer casing of the generator. One terminal supplies the rectified and regulated DC current from the generator, via a large diameter cable to the battery positive terminal. The second terminal provides the LIN bus connection between the regulator and the Engine Control Module (ECM)


PS the Alternator Output is Suppressed against RF Interference in Modern Cars (or should be) FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

This seems to becoming quite complicated  FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

Just a little update to this. I have just hardwired the unit into the passenger footwell fusebox, earthed to the bolts in that area and the noise is still there. FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎

I am running out of ideas.

Have you tried a filter in the actual 12v supply lead? - such as this, it does say that it is compatible with car audio system and does cure noise.

https://www.amazon.co.uk/Isolator-Suppress...&psc=1

Sorry we are not solving this (yet), I have no excuses as I have in the past solved many electrical and electromagnetic interference problems as part of my work. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Don’t apologise Ian! You and everyone else have been exceptionally helpful. It could well be the more complex things you suggested that could be the problem - I haven’t yet looked into those. I was hopeful that in hardwiring it in, which I was always going to do, would help solve the issue.

As for the inline filter, I haven’t tried that - that could be another option. FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental
Now greatly regret selling the Outlander. MPG of the FL2 is atrocious and so are the fuel bills. Fun though 😎