Load Sensor Wire Problem

[nafeun]

Hi all,

My 2004 VRS is poorly :( first time in 3 years.

3 years ago I suffered the usual battery drain problem and found the load sensor wire had snapped by the starter motor. At the time I managed to bodge it with some solder and it made a connection...just. My intention was to at some point make a proper repair.

That proper repair never did materialise and my bodge worked well up until 3 days ago when my wife lost power steering. I made the assumption that my solder had failed since I had no battery light on ignition on. I checked and it looked a poor connection so resoldered, however it still failed.

Therefore I cut all the connector out and replaced with fresh wire and crimps using good crimp connectors and good crimping tools. I'm still not getting the battery light :(

I have checked the colours match 3 times over and have checked all connections. Therefore I assume it has been damaged elsewhere in the loom.

Would this be the only logical suggestion? My plan of attack is to firstly check conductivity from alternator to ecu. If there is a problem I will replace the entire loom from alty to ecu.

To summarise, no battery light, dodgy wires repaired and still no battery light.

Questions.

1. Could be anything else?

2. What pin on the ecu is the load wire?

Cheers

Nath

[Steve Neate]

According to the 'Haynes Book of Lies', the blue wire goes to the electrical system control unit - pin 9 on a 18 way connector & the brown/red wire goes to engine management.

 

Have you scanned for faults?

 

SN

[nafeun]

Thanks for that no not yet as my friend with vagcom is currently away. All the tell tail signs are its load signal...power steering loss at random times and no bat light on ignition on

[Breezy_Pete]

Load sense/DFM wire doesn't affect the charge light in the clocks, it's the blue exciter wire that - if broken - results in no charge light. DFM breakage gives fault codes in the ECU, and things like an ASR warning light after 10 minutes running.

 

Check what voltages you get at the alternator two-way plug (unplugged from alt), relative to chassis ground. The blue exciter wire should have about 12V on it with ignition on, if the circuit is good between the control module in the cabin and there. The other one should be around 4.5-5V I believe. Edit @ 1300 on 22/04: Just went out and checked these numbers on my Polo (which is essentially the same as a Fabia) and got 11.2V for the exciter wire, and 4.5V for the DFM.

[nafeun]

Thank you for doing that, I ll have a look at the weekend with my mates vagcom and fathers volt meter. I ll post the resukts

[Breezy_Pete]

No problem. The main thing is, if you see zero volts (with ignition switched on!) at either of those connections, you can be pretty confident that wire is bust, somewhere.

[nafeun]

12v on the purple and 0v on the blue...

Alternator at 12.9 Amps on tickover and 14 when revved.

Help :( where does the blue wire enter the bulkhead ?

[Breezy_Pete]

Somewhere under the point where the driver's side wiper arm attaches, I think, but start by seeing whether the blue wire does have 12v at the nearest point of your repair to the main run of the loom, if that makes sense. Down at the bracket on the front of the gearbox.

[nafeun]

Already checked and it's a 0 so going to go as high up the loom I can and check the voltage there. I ll take a look Sunday :(

[Steamfan]

I have finally solved my NO battery light,   Bought 2 yards of speaker wire,  cut the two wires off alternator load plug spliced in speaker wires with terminal block ran one wire to ecu plug,  again cutting original wire about 2 inches out of ecu plug and joining new wire into it.

 

Then took off wipers and black plastic cover exposing the loom and wiper mechanism carefully peeled loom covering  found blue wire and cut it about 2 inches from where loom disapears under wiper motor and spliced the other speaker wire into it wrapping with electricians tape and gaffer tape for good measure and bingo.. battery light working on dash for first time in 9 months.

[nafeun]

Exactly what I plan on doing cheers pal

[nafeun]

Fixed I took the scuttle pannel off and spliced straight into the kicker blue wire, ran that back to the alternator and hey presto - I have a battery light on ignition it's a pretty simple job for someone with the same problem. Only problem for me was I had to get an engineer mate to make me a tool to take the wipers off.

All done and I'm happy once again

[avie rose]

I have finally solved my NO battery light,   Bought 2 yards of speaker wire,  cut the two wires off alternator load plug spliced in speaker wires with terminal block ran one wire to ecu plug,  again cutting original wire about 2 inches out of ecu plug and joining new wire into it.

Does this mean you can by-pass the connector at the gear box and just route it to the ECU? 

 

Also I seem to have some duplicate wiring colours in the loom to my ECU, so you know which pin the DMF wire goes to?

 

Cheers

[Breezy_Pete]

^Yes, you can wire direct without the plug/socket at the gearbox bracket. 

 

What year and engine code is the car? With that info I can probably tell you which engine ECU pin number the DFM wire goes to. 

The wire you want to fix if the battery light is not coming on with ignition is probably the other one though, the blue wire that goes through into the cabin; as per the other paragraph of Steamfan's post. 

I'm not sure on the diesels, but I know for a fact that on my petrol Polo (same electrics as equiv Fabia) the DFM wire being broken/disconnected doesn't alter the behaviour of the battery light (I've tried it with switches in line). Would be interesting to know if diesels are different in this respect. 

[Steamfan]

Does this mean you can by-pass the connector at the gear box and just route it to the ECU? 

 

Also I seem to have some duplicate wiring colours in the loom to my ECU, so you know which pin the DMF wire goes to?

 

Cheers

Yes by-passed the troublesome plugs next to gearbox altogether, simply ran wire straight to ecu.  Just remember disconnect battery and wait 15 minutes before unplugging ecu plugs I cannot remember which pin for DMF but it was easy to find the correct colour wire as I recall.

[avie rose]

Cheers guys.

wino - engine code is ASY (I think. Its an sdi) 2003/4.

The reason I asked about the dmf wire as well is because the alternator doesn't charge the battery until about 3000rpm.

Checked the voltages on the alternator connection for the exciter and dmf wires today and they read 11.8v and 6.4v respectively. This to me would seem to suggest that there is good continuity on both wires, no?

[Breezy_Pete]

Pin 38 of engine ECU then.

 

Those voltages do seem to indicate at least some connection on both, but I'm surprised by the value of the DFM one. I would expect the voltage on the (unplugged from alternator) DFM loom connection to be either near 5V (mine is around 4.5V) or near 12V (a couple of other diesel owners recently have said that they see a similar voltage on DFM to that on the L/blue wire connection). It depends how the ECU deals with the signal, which is actually an open collector/drain output from the alternator that the ECU can pull up to whatever voltage it likes internally.  When disconnected from the alt, the wire will 'float' up to whichever voltage rail it is pulled up to within the ECU.

 

Do you have a normal-behaving charge light in the cluster? Or not.

 

Although I've read (and repeated on here, in the past) that a bust DFM wire may cause the charging not to work at low revs, I'm not at all sure about it now, because I can't see how an 'information signal' from alternator to ECU can do this. It isn't, as is often said, a control signal from ECU to alternator. You can see the same signal coming from the alternator's voltage regulator, even when it isn't connected to the ECU, if you supply the necessary external pull-up voltage.

[avie rose]

I did until December have a normally functioning charge light, but had the alt changed for a new one because of the charging issues. Then couple of months ago realised that I didn't have the charge/batt light on ignition anymore.

I think I'll try bypassing the wires at some point, because the alt is new like I say as is the battery (~8 months).

Having said that, i can also having some other electrical issues, so perhaps it is just a gremlin that had moved into my car!

[Breezy_Pete]

Try running a new DFM wire from close to the alternator plug to close to ECU connector; but without doing anything to the blue wire. If your charge light and charging gets fixed, you'll have proved me wrong. (and fixed your car).

If it doesn't improve things, run a new blue wire.

[avie rose]

Try running a new DFM wire from close to the alternator plug to close to ECU connector; but without doing anything to the blue wire. If your charge light and charging gets fixed, you'll have proved me wrong. (and fixed your car).

If it doesn't improve things, run a new blue wire.

Your on sir! I shall get back to you with the results. Probably won't be until next week though as it is SWMBO's birthday this weekend so I can't really get away with spending it on the car.

Rookie question though. Why do I have to wait 15 mins before unplugging the ecu? Surely if the battery is disconnected there is no power in the circuits to short it on anything?