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

Reply to
lion_elk
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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).
Reply to
Peter K L Milnes

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.

Reply to
Steve

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

Reply to
lion_elk

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.

Reply to
lion_elk

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

Reply to
Gary Heston

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