Fault Code 02252 - Generator 004 - No Signal / Communication

This was an interesting one and caused me a lot of head scratching!

My Superb has the Stop Start function and is fitted with an AGM battery.

On the side of the alternator is a voltage regulator with a plug. On the negative terminal lead to the AGM Battery is a Control Unit, with a plug, which monitors and regulates the battery charge to enable / disable the start /stop function.

The wiring harness from the plug on the voltage regulator contains (what starts out as a yellow wire), which carries the data signal (Lin) from the voltage regulator on the alternator to several components, including the control unit on the negative lead to the battery. 

The above fault code usually indicates a likely problem with either the terminal plugs / connections on the voltage regulator or battery control unit and / or the wiring in between. Without the correct diagnostics equipment and ideally an oscilloscope to monitor the data signal, it is tempting to fear the worst and start replacing components such as the voltage regulator and / or the alternator.

This is an easy mistake to make as when there is no signal from the generator and you stick multimeter probes on the battery, with the car idling, it shows that the alternator is not charging the battery and this remains the case until the revs rise above a certain level, at which point the alternator kicks in and starts charging the battery again.

This can be a problem if the car is idling for a long time with the blower fan and other power hungry applications turned on, as the battery will discharge.

The plug on the voltage regulator is a very snug fit and difficult to access unless you have small hands (I don't)! The plug needs a really good push (I used the leverage of a screw driver handle to do this) to fully engage, at which point you will hear a click. If you don't hear the click it may seem that the plug is fully engaged but it won't be and this will be the cause of your problem. The other potential issue is a break in the wiring, normally the yellow data wire, which will need to be traced and replaced.

So what caused my problem? A few weeks ago I decided to fit a tuning module and mistakenly unplugged the voltage regulator plug instead of the turbo boost connector / plug below it. I quickly realised my mistake and thought I had fully engaged the connector but over time it must have worked loose causing this error code / problem!

I put up an earlier thread about battery adaption and am now thinking that this problem maybe linked!: 

Edited 21 December, 20223 yr by Smart Pro
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