Complete loss of electrical power when turning ignition

[aleksander.simonsen]

Hey,

As stated in the title, my polo 6r 1.6TDI blacks out completely when I turn the ignition from the neutral on position to the starting position. I do however get one click from the starting solenoid.

I have measured the battery voltage (12.6V) and in addition to this I measured 12.6V on the actual solenoid input. I have also measured the wiring resistance from ground to the battery and the battery to the solenoid, which appears to be fine. In addition to this I have measured the battery while attempting to start, this resulted in a voltage drop, so it seems like something is happening. Due to bad access I have not been able to make good measurements on the actual starter and the wire between the solenoid/starter.

I did suspect the solenoid to begin with, but I am frankly quite confused due to the complete electrical power loss. Could it be starter relay related? I don´t have access to proper wiring diagrams which makes it difficult to diagnose.

Any suggestions?

[ciclo]

Sounds to battery in poor condition.
Check how much the voltage drops when trying to start ... https://youtu.be/Eqw1CF1nOt8?t=139
Check if it starts with another battery.

[aleksander.simonsen]

Thanks for the fast reply. It is very much appreciated.

I did a measurement and it dropped down to about 9.5V. I also tried to jump start the car with the help of my other car with no luck.

[RUM4MO]

While the starter motor is connected I would expect to see that sort of voltage drop, if there was little or no voltage drop then the solenoid coil and/or the starter motor would be open circuit or had a wiring issue, early cars ended up with the solenoid coil supply wire fretting/corroding badly and so dropping a lot of voltage at that point, as long as you witnessed that voltage drop at the battery posts then it would not be that lead I'd reckon.

More investigation needed I think - though diagnosing faults at a distance can be hit and miss - sorry!

[aleksander.simonsen]

I tried to measure the voltage and resistance in the exposed braided wire between the solenoid and the starter. I found that there were connection for a split second.

Also the battery voltage remained low for perhaps 10 seconds after turning the key (While everything was blacked out in the cabin)

The engine does not crank, there is only a click in the solenoid.

[RUM4MO]

You would need to be able to measure the battery voltage all the time while trying to start it, typically via the 12V outlet, I have a plug with flying leads terminated via 2mm insulated sockets for that job and use an old style moving coil voltmeter as that type respond quickly to a fast changing battery voltage - a DVM can end up having a slow refresh rate if its a cheap one and so you don't witness the fully range of voltage during cranking.

Have you tried measuring the battery voltage while the ignition is on and the headlights on - and see how low it is under these conditions, it does sound a bit like a dying battery, I'm suggesting this in case the 9.6V you have witnessed is when only the starter solenoid is trying to switch the motor on and failing to fully move across due to lack of voltage.

[veteran]

Do these TDIs have a clutch-pedal position sensor (CPPS)? TSIs of 6R/6C type do, meaning that you can't turn the engine over and start the car until the CPPS is activated. These sensors were, on some 6Rs, situated at the clutch pedal, inside the cabin, but on later models were moved to the outside of the car, on the bulkhead, the other side from the clutch pedal. They have been known to fail.

Just a thought.

[iichel]

I can see where you're going veteran, but I suspect a faulty clutch position sensor would simply abort the starting process rather than a complete electrical shutdown of everything.

[aleksander.simonsen]

Thanks for good suggestions!

I´m just wondering if the attempt at jumpstarting the vehicle would rule out potensial battery issues? Also, headlights and all other lights including the instrument cluster and screen blacks out completely while in the ignition position, until the key is in the normal on position, if that is relevant.

I will definitely check the CPPS. However, would this result in complete black out? In my other car, not clutching only makes the car do nothing when I turn the ignition.

[Mikeso51]

Some thoughts:

If you get the same result with another known-good battery, then you can rule out the battery as being the problem.

If the voltage from a good battery drops dramatically and the electrics black out when you try to start, then clearly a lot of current is going somewhere. Since you can hear the solenoid pulling in, this would suggest that there is a major short circuit after the solenoid, or more likely that the starter motor has failed in some way. Could it be jammed?

I don’t know how easy it would be to disconnect the power feed to the starter motor, but disconnecting it and seeing what happens when you try to start would help isolate the problem area.

[veteran]

aleksander,

I presume that the half-dozen fuses controlling the high currents on your TDI are contained in a covered fusebox somewhere in the vicinity of the battery? I think it'd be worth inspecting those fuses and using a meter to measure the voltage on either sides of them when you try to start the engine and everything goes dead. If you find any sort of volt drop across any of them, you'll have at least found a clue of some sort (possible blown high-current fuse). You could get someone else to sit in the driver's seat and operate the ignition/starter, while you do the monitoring with the meter. For instance, it might well be that the voltage momentarily fed to the starter motor (as opposed to the low-current voltage fed to the solenoid to enable the solenoid to switch that starter-motor voltage) uses one of those high-current fuses. If so and the fuse has blown, then you'd get the symptom of hearing the solenoid click but no voltage then appearing on the starter motor.

If, as you seem to be saying, the battery voltage appears to quite good (you state 12.6v) under quiescent conditions such as with just the ignition on, then normally an attempted starting of the engine would cause that to drop to maybe 8v or so for a fraction of a second and then recover to 12v or above. But if the battery is on its last legs it'd drop much further than that. So again, why not get somebody to do the business in the driver's seat while you monitor the battery voltage (right on the battery terminals) with the meter?

Hope you soon discover the cause, as the situation you have must be infuriating.

[RUM4MO]

One maybe final thought, the blanking out of the dash lights etc will be due to the supporting power supply relay contacts opening due to a dramatic drop in the battery voltage, so change doing what I suggested to fitting the DVM leads directly across the battery posts using crok clips - if you were lucky enough to own a moving coil multi meter, you would see the true voltage drop under the "starting" conditions, either swop batteries or connect the other car to this car using HD jump leads, if the car can now start you know that the battery is the issue, the wiser move would be to temp swop batteries though!