GROM VOL01B3 Bluetooth Car kit for select Volvo 01-07 Review

by David French


Recently I “upgraded” my 2008 Volvo V50 to a 2002 V70 model. (Yes, it’s older, but I’m starting to think cars have got too complicated for their own good now… sometimes older can be simpler and more reliable.)
I drive a lot, and in the UK it’s illegal (not to mention dangerous) to use a handheld mobile phone whilst driving.

The V50 had a Bluetooth-enabled head unit which worked fine with my iPhone, but this only accepted voice calls. In order to play stereo audio, I bought a separate cigar-lighter Bluetooth receiver which paired with the phone and provided an aux out; however, of course there was no Aux In in the V50 head unit.
The solution was to buy a Sonichi DAB radio, which rebroadcasts the DAB channel onto FM, and handily also has an Aux In feature. So I could play my phone’s audio to the Bluetooth receiver, which then output to the Sonichi, which then rebroadcast over FM to the Volvo head unit… This worked surprisingly well, but the audio quality wasn’t brilliant, and it was a bit of a bodge job really.

The new V70’s head unit, a Volvo HU-603, comes from an era before Bluetooth was widely used, and also doesn’t have an Aux In. I initially set up the same Bluetooth / Sonichi mashup, but this time round I was relying on the Bluetooth unit to handle voice calls too. This was more problematic, as it was unreliable (outgoing calls routed through Bluetooth but not incoming ones), had no external mic, and I had to switch the Sonichi to Aux In every time I wanted to make or receive a call. Time for a rethink.
My original plan was to add a cabled Aux In to the HU-603, which led me by a roundabout route to GROM Audio.


A few forum users recommended their gear, and a hunt around their website confirmed they supported the Volvo head unit, with a range of products. Of greater interest was the BT3 Bluetooth interface, which is a standard module with leads available to
connect to a variety of manufacturers’ head units. The clincher which attracted my order was the option to add a cabled Aux In to the Bluetooth module. (It actually accepts up to two external inputs in addition to the Bluetooth functionality.) £120 including shipping later, and my GROM BT3 was on the way, complete with Volvo HU adapter and external USB out and Aux In.

Out Of The Box
The GROM arrived in a jiffy bag, containing:
• The main BT3 Bluetooth unit
• A cable specific to my Volvo HU head unit
• An external microphone, which was of surprisingly good quality with plenty of cable and a 3M sticky mount & bracket
• The additional cable I’d ordered with USB output (female) and Aux In (headphone jack, male)
• A set of instructions covering the Volvo HU cable, and a user manual for the BT3

The GROM user manual was of refreshingly good quality compared to a lot of manuals you get, which are often translated from Chinese or Japanese quite badly. The first task I faced was removing the Volvo head unit. This isn’t simply a case of sticking a couple of bits of wire down the side and pulling it out, as with many head units. Instead you have to remove the pen holder at the base of the dashboard, then the heating / air conditioning control panel, and finally the head unit.

Fortunately I found a video on YouTube which explained this in all the necessary detail. It’s not entirely surprising that the GROM instructions don’t aim to cover head unit removal details for all potential models and head units, but a huge amount of information is available on YouTube. At this point I made my one mistake. My V70 is an Auto model, and the gearstick was in the way of removing the aircon control panel fully, so I turned the ignition to Position II in order to release the gearstick. Unfortunately the ECU panicked at not being able to see the aircon ECU, and immediately stuck an “Airbag / SRS Fault” warning on the dashboard. Ultimately I had to visit a Volvo independent service center to get this warning reset, which kindly they did at no charge. DIY installer beware. Once the head unit was out, the HU cable connected directly to the CD auto changer DIN connector, and also needed splicing into a permanent live feed in the head unit harness.

GROM provide clear and unambiguous instructions on how to do this, and also a proprietary connector to intercept the live cable without having to cut it or damage it irreversibly. Finally, the cable needed to be earthed; this was simply a case of screwing the supplied spade connector to a spare screw on the head unit. This was the only part of the instructions on which a non-technical user might have been unclear. The HU cable then plugged into the BT3 unit. The cable is long enough to fit the BT3 elsewhere, for example behind the glove box as GROM recommend, but in the V70 there was enough space around the back of the head unit to leave it there. I nestled it to one side behind the dashboard; the manual refers to securing it with Velcro strips, but these weren’t provided with mine.

The next step was to connect the microphone. It’s recommended you fit this away from doors and windows, to avoid road noise. I fitted mine up by the rear view mirror, and it’s easy to run the cable along the headlining and down the rubber seal of the A-post to the dashboard. Once installed, the cable is entirely concealed. The decent length of cable supplied assists with this.

GROM Volvo Bluetooth Integration

Finally I connected the USB Out / Aux In lead, and ran it behind the dashboard to the far side of the steering wheel. In my case I wanted to use the USB Out to power my Sonichi DAB radio, and the Aux In to take the audio feed from it. This was simple enough – I needed a USB A to Mini USB cable to go from the GROM lead to the Sonichi – and the excess wiring tucked back under the dash beneath the steering wheel.

GROM recommend disconnecting and reconnecting the head unit to make sure it recognizes the BT3, which it will see as a CD autochanger, and it made sense to do this now before reassembling everything, rather than having to take it all apart again later. I also tested everything was working before refitting the head unit, aircon controls and pen holder. On power-up the head unit saw the GROM as a CD auto changer, and we were in business.

In Use

Pairing between the phone and the head unit is simple; GROM state it has to be done within 3 minutes of powering up the head unit and vehicle, but later I found this wasn’t necessarily the case. Once paired, the BT3 will switch to the Bluetooth audio channel when it detects stereo (A2DP) audio or an active phone call. If it detects no Bluetooth activity, even when the phone is paired and in range, it defaults to the Aux In (in my case the Sonichi DAB radio). This is exactly the behavior which you’d want, and it works well.

The first thing I noticed was the sound quality, which was excellent. Volvo sound systems always punch above their weight, and having audio fed via a cabled input to the head unit, rather than re-transmitted through FM, makes a considerable difference to the clarity and fidelity of the audio. A2DP audio is clear, crisp and undistorted, and the analogue Aux In from the Sonichi was likewise more than satisfactory. At this point I also noticed that the USB Out from the BT3 powered the Sonichi with a smoother supply than the cigar adapter I’d previously used. I’d noticed before that the Sonichi suffers noticeably from interference and dropout when powered by a substandard USB supply.

With the BT3, it’s completely happy with the USB power, leading to a more stable connection with few dropouts. Conveniently, the USB power stays on for a few seconds when the ignition is turned off, before shutting down (which powers off the Sonichi); this means when you restart the engine from warm, you don’t have to keep powering the DAB radio (or whatever USB device you have attached) each time. Little details like this make a difference. I’d hoped the outward quality of the mic would turn out to extend to its innards too, and I wasn’t disappointed.

The audio quality for hands-free calling is excellent, with the third party unable to hear any background noise at all at speeds up to 70mph. I’ve used several in-car phone systems, both OEM and external, and the audio quality of the GROM system beats all others I’ve tried. The steering wheel controls on my V70 allow track forward / back, and this works seamlessly with the phone. Here GROM have thought ahead again: I was unreasonably delighted to find that a double-tap (or long press) on the Scan button on the head unit triggered Siri on the iPhone. This opens up access to proper hands-free use and is invaluable. My head unit doesn’t seem to display track information text, but GROM suggest some head units may allow this if configured to see the BT3 as a minidisc player (although you may then lose steering wheel controls). There have been a couple of issues (once every 8 weeks or so) with the audio not being switched correctly, or the phone not connecting. This is easily solved by power-cycling the unit or re-pairing the devices. An issue with incoming phone calls not routing correctly through the GROM was quickly solved by GROM technical support pointing me towards an Accessibility setting on the phone I didn’t even know existed. What little support I’ve needed has been very good.

The GROM unit isn’t particularly cheap, but in terms of quality you do get what you pay for. As a way to bring a dated head unit into the 21st century, adding on all the functionality you’d expect from a high-end Bluetooth-equipped unit, it’s unbeatable.
Fitting, on this model at least, is well within the reach of anybody who is handy with a basic set of tools. If you’re tempted, go for it – you won’t be dissatisfied.

Image source: GROM Audio

newest oldest most voted
Notify of

I have one of GROM kits for my car, and I really like it.