Help needed with reversing sensors

[mikejkay]

I am now on my fourth set of reversing sensors. I have had two wireless and two wired setups. All seem to last for six months to a year and then fail.

 

Before buying a fifth set I decided to carry out an investigation and have discovered that the voltage at my reversing light is 11.3v. All the systems are supposed to operate at this voltage. If I run wires from the 12v socket inside my habitation doorway (which gives 12.99v) my latest wired system works fine. When plugged into the wires attached to the reversing light it does not. Out of curiosity I checked the other "failed" systems. One worked, one worked but intermittently and the third was dead.

 

I am at a loss as to what to do as the problem appears to lie with the vehicle electrics. The only option that I can come up with is to run a power wire to the control unit and operate the reversing sensors manually.

 

Van is a newish (2016) Hymer exsis-t 414. There is no visible corrosion of the light unit and, as already stated, the voltage at the bulb is 11.3v.

 

Any bright spark got any ideas?

 

[Alanb]

Hi Mike,

 

I keep thinking about reversing sensors, but still send my wife to the rear instead. Your experience does not encourage me.

 

Given the age of your vehicle, I assume that it employs CANBUS. Our 2006 PVC does not have this system, but our more recent SAAB and SKODA do. As the CANBUS switching output is electronis it will probably result in a greater voltage drop than metallic switch contacts. Couple that with the trend to thin wires selected for current rating rather than voltage drop.

 

If you install a power wire, why not add a relay as well. If you energise the relay coil from the reversing light circuit, you could retain the automatic function. A Micro Automotive Relay with diode and base could be almost tied to a cable form. I would recommend a relay with diode to protect the canbus from voltage spikes generated when the relay releases, if the reversing light bulb should fail.

 

Alan

[Billggski]

Is the 11.3 volt with the engine off, running, or at tick over? When reversing it may be higher.

[mikejkay]

Alan,

 

Thanks for that suggestion. I shall let things meander around the dark recesses of my mind and try and work something out. It may be that I can beef up the supply wire to the reversing light. FYI the Hymer does have a CANBUS system. The wires from the reversing light to the main reversing sensors unit are short and, as you say, very thin (24 AWG?). However, there is virtually no voltage drop between the bulb terminal and the plug, measured with a good quality multimeter. What worries me is the low voltage at the bulb. I will try and measure this again when the engine is running but for that I need someone to help by depressing the clutch. At the moment I am sans wife so this will have to wait.

[Derek Uzzell]

This advert

 

http://www.ebay.co.uk/itm/CISBO-CAR-REAR-REVERSE-PARKING-SENSORS-4-SENSOR-AUDIBLE-LED-DISPLAY-CANBUS-KIT-/220500702597

 

warns

 

"If a non-CANBUS parking sensor kit is fitted to a CANBUS car, the computer in the car detects an extra device connected which then causes the voltage to drop, causing the kit to malfunction.”

 

but I’m not sure that would apply to a 2016 Ducato.

 

I’m guessing that, when reversing sensors are a Fiat factory-fit, the reverse-gear switch on the gearbox is used as a trigger rather than a reversing light being used as the power source.

[mikejkay]

Derek

 

Thanks for that. I know that fitting add-on electrics to a CANBUS vehicle can cause problems but I don't think that this can be the case here. Firstly because all my fitted reversing sensor installations have worked satisfactorily for a while and, secondly, because the low voltages measured have been when the control box, display and sensors have been disconnected. In the absence of any evidence of corrosion I can see no reason why the systems have stopped working in-situ but will work when a separate slightly higher voltage is applied independently. I'm tearing my hair out >:-(

[mikejkay]

Billggski - 2017-11-04 11:33 PM

 

Is the 11.3 volt with the engine off, running, or at tick over? When reversing it may be higher.

 

Engine off. Will try engine running when errant wife deigns to reappear.