Please Help with electrical problem!! Battery issue

[Sebpt]

Hi Everyone,

I made a mistake by installing the battery +/- in reverse polarity. I was rushing around and did not pay any attention to what I was doing!!! The radiator fan then started working backwards.

After installing the battery back on right (this time), I got a battery light indicator on my dash board. Then I scanned the car with Vag-com and I got thrown a code about the ECU not working properly. The alternator current sensor is not working and the radio is also fried. I checked the fuses and they are ok.

My questions are:

1) What can I do to remove the battery check light? (I all ready erased the code with Vag-com)
2) How can I re-set the ECU?
3) Has anyone ever experienced anything similar to this before?

Thank you for your help!

Sebastien.

 

[outatime]

You can reset the ECU by taken the positive and negative wires (with the car disconnect from the battery) and hold them together. This drains all the residual energy from all the systems. Hold it for a minute and if possible have someone turn on the lights and hold the brakes down. This will draw all the energy out of the computer thus reseting everything.

Rocco

 

[Sebpt]

This will draw all the energy out of the computer thus reseting everything.

Rocco

How can the electrical system have a "reserve" or residual capacity when the battery is unplugged? I just don't get it.

Will this remove the red battery light on my dash? Do I need to reset with Vag-Com?

 

[Wook660]

Doesn't doing that have the potential of frying the alternator?

 

[Sebpt]

Doesn't doing that have the potential of frying the alternator?

I would think the alternator has power only when the belt is turning

 

[bam_bam_dip]

I would think the alternator has power only when the belt is turning

I would agree that the alt. doesn't have any capacitors on it, but as far as the ecm, man, thats a crap shoot......YMMV

 

[Sebpt]

Anybody experienced this?

 

[Powder Hound]

How can the electrical system have a "reserve" or residual capacity when the battery is unplugged? I just don't get it. ...

Any system with as many electronic components as are in these cars is going to have lots of little filter components, which take the form of capacitors. Capacitors by nature store electrical charges. They filter by absorbing and storing voltage spikes, thus causing the spikes not to be propagated after the capacitor.

When the system is turned off, the stored charges leak back out of the capacitors, and the time it takes for the charges to leak out depends on the characteristics of the system. Most caps can leak out pretty fast, but it makes sense that if you short the unconnected terminals at the battery for a minute or so, then you'd be safe.

If you don't do this, then there is no guarantee that some energy is not stored and maintaining states (error codes or failure states) in the ECU.

 

[Nutsnbolts]

There is a possibility that the battery light (which is not removable unless you want to de-solder it from the printed circuit board) is being turned on because the diodes in the alternator were fried when the battery was hooked up the wrong way. In that case, one or more phases of the alternator's output would not be contributing to the overall electrical system condition. It is possible that the ECM is seeing that. Also, in order to "clear" the ECM, DO NOT connect the terminals together. Just pull the negative cable off of the battery, and leave it off for 1 minute. Then, hook it back up and see if that clears the codes.

-Rich

 

[Dodoma]

Always keep a hammer. If the problem does not get solved, at least you can use the hammer to bang.

 

[Sebpt]

There is a possibility that the battery light (which is not removable unless you want to de-solder it from the printed circuit board) is being turned on because the diodes in the alternator were fried when the battery was hooked up the wrong way. In that case, one or more phases of the alternator's output would not be contributing to the overall electrical system condition. It is possible that the ECM is seeing that. Also, in order to "clear" the ECM, DO NOT connect the terminals together. Just pull the negative cable off of the battery, and leave it off for 1 minute. Then, hook it back up and see if that clears the codes.

-Rich

Would the alternator be still charging?

 

[Nutsnbolts]

Sebpt:

Yes, the alternator can still charge on 2 phases out of 3, and maybe even on 1 phase if the electrical drain is light. It will be pulsed output, but so fast that we wouldn't see it. However, the ECM might...

-Rich

 

[Sebpt]

Sebpt:

Yes, the alternator can still charge on 2 phases out of 3, and maybe even on 1 phase if the electrical drain is light. It will be pulsed output, but so fast that we wouldn't see it. However, the ECM might...

-Rich

Thanks Rich for the reply. I will get the alternator checked on monday and do the trick with draining the power system (unplug negative post). Hopefully I will remove the battery light.

 

[Sebpt]

Sebpt:

Yes, the alternator can still charge on 2 phases out of 3, and maybe even on 1 phase if the electrical drain is light. It will be pulsed output, but so fast that we wouldn't see it. However, the ECM might...

-Rich

Would I need to relace the whole altenator? Can it be fixed?

 

[Nutsnbolts]

If you take the alternator to a rebuilder, they should be able to bench test it to see if it needs any work first, then fix it for you- it may only need a rectifier, and possibly a regulator. The bearings within it should be fine, so they may not have to take the whole thing apart.

Some repair shops can even do this service. See if there is someone in your area that could test it for you, and repair it. I'm all about repair and reuse instead of remove and replace!

Let us know how you make out...

-Rich

 

[PDJetta]

How can the electrical system have a "reserve" or residual capacity when the battery is unplugged? I just don't get it.

Will this remove the red battery light on my dash? Do I need to reset with Vag-Com?

Capicitors in the ECU, perhaps?

--Nate

 

[PDJetta]

Yea, get the alternator tested. Perhaps just the voltage regulator went out, not the rectifier diodes in the alternator.

--Nate

 

[Dick_Larimore]

It is almost a certainty that you shorted the alternator bridge diodes. The bridge conducts virtually unlimited current when the battery is connected backwards. The voltage regulator will likely be OK. Your only option will be to replace the alternator. Check the fuses over the battery box. You likely blew fuse S176 which is the output fuse from the alternator. If you are really really lucky, the fuse saved your alternator.

 

[Sebpt]

It is almost a certainty that you shorted the alternator bridge diodes. The bridge conducts virtually unlimited current when the battery is connected backwards. The voltage regulator will likely be OK. Your only option will be to replace the alternator. Check the fuses over the battery box. You likely blew fuse S176 which is the output fuse from the alternator. If you are really really lucky, the fuse saved your alternator.

The fuses are okay but the alternator is not charging. I am getting it replaced this morning.

 

[Sebpt]

Let us know how you make out...

-Rich

Alternator replaced - also bearing was loose. 14.5 V charge and back in business!!

Thanks for the input

 

[Nutsnbolts]

Sweeeeeeeet.

 

[craig01b]

Yup, diodes tend to die quicker than fuses react.....Not the best way to learn, but mistakes like that we tend not to forget....

And we all make mistakes from time to time.

Craig