skoda roomster 1.4 tdi strange voltage drop problem.

[imrasl]

any one can help me .... plz my skoda 1.4 tdi strange intermittent problem abs, parquing brake light , then steering wheel light and power steering loss.. voltage drop at a level tht engine missfire instrument cluster go off. but after shutting down engine start again all ok. ive checked all fuses nothing blown... local mechanic after diagnose suggest me change battery .. but even after battery change problem keep coming. i am sharing a link to see the problem..

 

[Mongler98]

clearly don't go back to that mechanic
What is the voltage output of the alternator at idle and while driving. you can test it with someone testing the 12v plug (cig lighter) while you drive. High RPMs could show that the voltage stops charging but it will at low. common symptom of a dead alternator with no more brushes left!

 

[imrasl]

thnks for reply. i have checked on idle on battery terminals show 14.4 ... bt not checked while driving... i will do tht and post the result.... if alternator faulty ... how battery could be charged.. there is no warning of battery when tht occur... and how it is fine after shutting and starting again.

 

[Tdijarhead]

Your new battery sounds a bit weak. Which probably means the alternator is not charging properly. Low voltage in the electrical system can cause a multitude of random codes and weird issues.

With a multimeter check the voltage output of the alternator at the stud on the back of the alternator where the battery cable connects. It should be around 14v with the car running. Then check the voltage at the end of the cable at the positive battery terminal. The reading should be the same.

 

[Mongler98]

the car will give codes when things do not get enough power
the alternator is a smart one, it will control charging
When driving at higher than idle RPMs the brushes (if spent) will float and not cause charging
restarting the car will reset everything and it will work again until you reach higher RPMs

i had the same issue with a few cars before, anything past 3500 and it would stop putting out 14 volts
you will know when the voltage drops to 12.6 or lower at the 12v cigarette lighter port (easiest while driving)
be safe
14.2 to 14.6 is correct voltage when operating
12.6 to 12.9 is a fully charge new battery in perfect health
12.4 to 12.6 is technically a low charge but for an old battery is still in the acceptable range or on a new battery it is half charge but still may crank the engine over
anything lower than 12.4 volts is a low charge and may not be enough volts for the car to operate properly.
the voltage will be lower if not charging when running but engine off will be higher because of now draw.

i know there is a language barrier so i'm trying to be simple

 

[imrasl]

i will check and post the update.

 

[imrasl]

checked voltage around battery teeminals 14.33v
https://drive.google.com/file/d/1-LNe6YoXiH3gdTkQUd4dn4ahVbZqtHLW/view?usp=drivesdk

on alterneator 14.35v
https://drive.google.com/file/d/1-byNOsZw3sZ2PiU0p58meOW4iWBw4hH3/view?usp=drivesdk

checked on cig lighter on idle rpm and on 3500rpm

checked on cig lighter with full load

bt there was no warning light at tht moment i believe it come while driving.

 

[Seatman]

Might be worth checking the wiring to the plug for the brush pack, I left mine off once after fitting a new part and got some weird random faults but the meter still showed the alternator was charging, I think maybe the ecu wasn't getting the proper signal or something though so upset it. Mines a 2007 2L tdi but I'd imagine a lot of the issues are the same on most of these cars.

 

[Mongler98]

looks like your alternator is just fine. 14.3 indicates a worn down stator but not gone yet. the fact its not dropping out means its fine and your issue is elsewhere. i would suspect the battery but if your having these codes pop up with 14. whatever volts... yea... not sure whats going on here...

 

[imrasl]

looks like your alternator is just fine. 14.3 indicates a worn down stator but not gone yet. the fact its not dropping out means its fine and your issue is elsewhere. i would suspect the battery but if your having these codes pop up with 14. whatever volts... yea... not sure whats going on here...

i have checked voltage on cig lighter....after switching off when warning lights came. there was 4.05 volts ... no lights on instrument cluster when switch on but not crank. after cranking voltage jump to 13.79 - 13.98 volts..... could be sign of alternator ?? that sudden drop...

 

[imrasl]

Might be worth checking the wiring to the plug for the brush pack, I left mine off once after fitting a new part and got some weird random faults but the meter still showed the alternator was charging, I think maybe the ecu wasn't getting the proper signal or something though so upset it. Mines a 2007 2L tdi but I'd imagine a lot of the issues are the same on most of these cars.

i will check.....but there is no work done in engine bay for months

 

[Tdijarhead]

On the US models there are several grounds under the battery tray. This is sounding like a bad connection somewhere to have a voltage drop to 4v and then it comes back to 13+. Check your connections on everything, battery, fuse block on battery, grounds under the battery tray, big ground at the top of the bell housing, everything.

 

[imrasl]

checked earth points below battery tray all fine about 0.8 ohm. no rust

 

[imrasl]

when fault appeared, i have checked extracting fuses one by one to find problematic circuit but can not found any fuses that could lead to solution,

i found battery earth point hot.

any more help.

 

[imrasl]

although battery main negative cable look good. just in case i disconnect and clean well and connected again. fault not apeared again. i wait a week to confirm. so finally solved.

thnks for all to help me.