VW Tiguan electrical problem

[ScotUk5432]

Hi,
In need of any advice please

• electrical fault starting with rear parking sensor failing (dash states unavailable/dirty)
• Sensor is clean
• 12.3v on inspection of the battery at idle (ancillary equipment off).
• Due to low voltage my garage initially thought it was a faulty alternator so fitted brand new one (didn’t resolve sensor fault)
• The garage recharged the battery and first 20 miles no fault. however on driving the next day the parking sensor fault reoccurred.
• My garage then changed 1x parking sensor as one had a scratch. However this still didn’t resolve the fault.
• battery tested after changing alternator now is still 12.3v-13.3v at idle depending on what ancillary equipment running. Typically less than 12.7v.
• tested and found near zero parasitic loss

Any thoughts?

 

[plugsandsparks]

Is the only actual fault, parking sensor, if so have you tried to hear if you can hear the clicking noise from each one. A faulty sensor is common.

I dont understand the business about the battery voltage as nowadays batteries are often under management control and as such the voltage can be very variable. A better test would be when the car is fully loaded with lights, heated screen, heated seats and any one things you can switch on.

 

[static zap]

Charge your battery by other means , and get it tested ?
( have seen this new Calcium battery tech ..Fox the fault finding process ...)
If can borrow another battery.. may give charging clues.

 

[ScotUk5432]

Is the only actual fault, parking sensor, if so have you tried to hear if you can hear the clicking noise from each one. A faulty sensor is common.

I dont understand the business about the battery voltage as nowadays batteries are often under management control and as such the voltage can be very variable. A better test would be when the car is fully loaded with lights, heated screen, heated seats and any one things you can switch on.

Thanks, having driven it more this evening I am definitely finding that the charging rate is variable like you suggest. This morning it was barely charging atall (with sensor failed) and this evening perfectly fine, fully charged battery after a 20 min drive and no parking sensor fault.

what approx voltage would you expect fully loaded?

 

[ScotUk5432]

Charge your battery by other means , and get it tested ?
( have seen this new Calcium battery tech ..Fox the fault finding process ...)
If can borrow another battery.. may give charging clues.

Thanks for the suggestions. Do you think a dodgy battery could manifest with an intermittent parking sensor failure?

From doing some tests I get the feeling that the charging rate is very variable , sometimes barely putting any charge into the battery, when the battery is at full charge I don’t seem to experience the fault but when the system is not charging it seems I get the fault (not sure just a hunch)

 

[plugsandsparks]

You need to be careful where you measure the voltage as there are important losses in the wiring.
The battery needs at least 13V for a float charge. So with it fully loaded with accessories and held at 2500rpm for petrol and around 1500 for diesel you need 13V at the battery, preferably 13.7 to 14V if the battery needs a good charge. Sadly at idle you will run into instability wrt to the charging so get someone to hold the revs whilst you measure at the battery terminals
Hope this helps

 

[static zap]

Have seen peculiar , loosing 1 cell on starting ..agressive charging ,
high currents ,but struggling for a while to get Odd Cell working.

That showed up on a Citroen that without the engine running would barely run the radio for 5 minutes at low volume , before management turned it off with ECO mode.
A 3 month old faulty batch of batteries ..that helped send my local independent Accessory Shop into calling time.
If the engine is relatively cool and the alternator working hard . it may warm up quickly (without any instruments to hand).
(a distinctive whine can be hear in some drive belts - under high load )
..The ECU or what ever Body control etc .. manage accesories if battery voltage is too low ... Engine fails LAST.

 

[Mike Johnson]

I would suspect dirty connection to the parking sensor or an insulation fault on the wiring, perhaps between two sensors.

 

[ScotUk5432]

Many thanks for all your useful comments. Car is in garage next week and will update the thread with the cause

 

[Mike Johnson]

Guarantee it will need four new sensors and a new control unit, perhaps even a new wiring harness. ?

 

[plugsandsparks]

Ha, i will go for New Battery, alternator, wiring loom, sensors, controller, dash. Only way to be sure, lol