Electrical issues questions - P1 C30

Post by **scot850** » 12 May 2025, 14:20

Yes, this is the wrong forum, but i'm not getting any responses in the P1 forum. This question is for a general electrical issue, or even if it is an issue.

So background. Owner has problems with car going into limp mode when it warms up. If they stopped the car, switched off, waited a short time, the car would restart and run again for a while normally.

I am just starting the electrical gremlin chasing. Car starts ok. However as it has been standing I checked the battery and it was at 12.3V.

So before using Vida I decided to put it on a trickle charger as I would not be able to get to it until today.

The question. When I was connecting the trickle charger, as normal I connected the +ve connector to the battery and as the battery is still connected I connect the -ve lead to an engine ground or a suitably accessible engine bolt. Normally no issue. The trickle charger is not connected to power at this point. So why then was I getting sparking from the ground leak when trying to connect it when it is not connected to any power? I appreciate you are connecting effectively a wire between 2 points, but at that point I'd not expect a spark, never had this before. Does this mean a potential short somewhere in the car?

I'm looking for general feedback not necessarily to a P1.

My plan is once I have done a Vida diagnostic on the car and retrieved any codes, I plan to disconnect the battery to do some other work on the electrical system. But one of those tests will be a current draw to see if anything is drawing down on the electrical system. The owner did find one of the engine grounds had not been re-connected by a repair shop.

Thanks,

Neil.

Vova585 · Post by **Vova585** » 12 May 2025, 15:30

Option 1) take the same charger and test it at the other car. If it behaves the same: problem is in within the charger vs normal operating condition based on the charges age/build in protection against reverse polarity/etc
Option 2)(IMHO most likely in your case) bad engine ground. If the car behaves erratically try to put a jumper cable leads to the negative terminal and 1 wire to the body and another to the engine.
You need to narrow it down to what is not working upon it "acting up" spark,fuel and dig into that direction. I would get some needle probes and get access to the fuel pump connector, ignition coil(not sure of 1 vs 5 coil system vs 4 cyl) and injector feed/control. Good luck.

Post by **abscate** » 12 May 2025, 18:01

You are connecting a circuit internal to the charger when you clip up, even if it isn’t plugged in. A spark is normal

Post by **scot850** » 12 May 2025, 23:44

I have not seen this happen with our other cars so this is the first time I have seen this behavior. That was why I was asking. Thanks for the help guys, and by the look of it I am going to need all the help I can get!

Neil.

Post by **abscate** » 13 May 2025, 01:16

You only get a spaRk on caRs in albeRta

Post by **jonesg** » 13 May 2025, 01:48

normal, the transformer high side is a complete circuit, otherwise you wouldn't be able to ohm test the output to test for continuity.
The 120v side is also a complete circuit, the two sides are isolated by the transformer design.

Post by **chrism** » 13 May 2025, 05:46

We had a 2005 S80 that displayed these symptoms - worse in hot weather. The fault codes pointed to something awry with the throttle circuit. In the end the problem was cured by pulling the ECM and reseating it in its connector. The wiring between the ECM and the throttle body is also a common point of failure. It will be interesting to see what VIDA finds.

Keep us posted as to what you find.

Post by **scot850** » 13 May 2025, 14:07

So, got a few moments to check the car a little further.

After charging the car and immediately after disconnecting the charger, the battery voltage read 12.7V. Having left the car over a few hours and check the resting voltage. It had dropped to 12.45V. Leaving it overnight and now it is at a steady 12.35V. Does seem low to me. However the owner says no issues over the cold winter days. I'm not surprised! I have never seen as big a battery in a Volvo with a 5 cylinder engine. Can't upload the battery pictures just now, but it is a 970A/790 CCA battery! Low voltage but lots of Amps. Is the Voltage threshold an issue as I know the engines don't like low voltages??

Edit: Battery pictures:

: Small car - huge battery

: Battery fill battery tray

So did a battery drain test. Again a huge spark when connecting to the battery terminal! meter read 2.5A drain?? After maybe 15-20 secs the current drain dropped to 0.005A? Disconnecting, and testing again got the same result? What would cause this initial drain?

Inputs appreciated!

Neil.

Post by **abscate** » 13 May 2025, 14:30

Each time you disconnect the battery you reset the ECU and other modules, when you connect they c9mr alive and go through some routines before settling down.

0,050 Amp is a reasonable quiet drain, 0,005 Amp is really low drain

Post by **scot850** » 13 May 2025, 15:50

Ok, that makes sense even to me. But that is quite the battery pull from the various modules!

That drain is remarkably low I agree. I think the lowest I have seen is around 0.010A from an early 850. My V70R (MY00) runs around 0.045A as it has an aftermarket security system. So battery drain is not an issue.

Question still stands. On battery voltage. Is 12.35V no low in voltage terms? Once I have done all my wiring tests without the battery attached, I will run a charge test as the owner found one of the main ground cables had not been reconnected after the head swap. I wan to ensure the alternator is running ok as they do run hot in these cars due to the position they are mounted, low airflow and the turbo being nearby. Want to try to eliminate charging system/battery are not part of the equation.

Thanks for help guys!

Neil.