reversing aid sensors malfunction

I had a 1998 Volvo S40 (non-automatic) and fitted a Parking Partner
reversing sensor kit, taking power by tapping into the reverse lamp
lead, and it worked perfectly.

I now have a 2003 Volvo S40 automatic. The body is essentially the same
but the electrics are more sophisticated and less accessible. I asked
my local (non-Volvo) auto engineers to fit the same kit but it
repeatedly fired off erratically when nothing was there to trigger the
sensors. This persisted in spite of trying different earthing points
and fitting a diode on the 'power' side of the kit (as suggested by the
kit supplier).

The local lads substituted a different make of reversing aid and it
does the same (but worse!). Before trying to run it from an
alternative 12V DC source (to be switched on/off via a reIay on the
reverse light circuit), we have tried some logical experiments.

The guys told me that it worked OK when powered by a stand-alone 12V DC
battery.

But when powered from the vehicle's built-in 12V DC cigar lighter
connector it starts to malfunction (unpredictably) as soon as there is
any change in electrical function e.g. if the footbrake is applied, the
windows lowered or whenever the engine is running. It even fires off
spotaneously every 8 seconds when there is nothing obvious happening to
account for a voltage change!

Apart from using a (non-autochargeable) 12V battery pack and replacing
it when it goes flat, I can't think how to resolve this - can you?

Lionel

 

Make sure that all earth (ground) connections in the affected lighting
circuits are up to scratch and that there is no interference with the "bulb
out" circuitry. You are getting too much of a Volt drop through your other
lighting circuits (possibly due to bulb failure relay) in the common ground
(earth) connections.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

Run a small gauge wire under the car where it's away from moving and hot
parts. Install a small fusable link. Attach directly to the battery.

 

Peter - thanks. I don't unerstand how to identify which ground
coonections need attention, nor how to check 'bulb-out' function. I'll
pass it on to the garage guy anyway.

Lionel

 

Steve - this sounds too good to be true - presumably the car battery is
not subject to the voltage fluctuations happening on the 'other side'
of the electronically-controlled system such as the cigar-lighter and
various lighting circuits.

Thanks, Lionel.

 

The battery isn't as subject to them, but the voltage won't change as
much at the terminal as it will after going through several feet of
relatively small diameter wire. Copper is resistive, and there will be
voltage drop over a run of it, in proportion to current flow. When the
current changes (blower switching on/off, brake lights, turn signals,
etc.) you get voltage drops and spikes.

You can also reduce this problem by using a filter at your reversing
sensors' power connection.


Gary