UEC advise please, got an issue with the horn that I dont believe is CIM related

[sean-tek]

Hi All,

Got an issue with the horn not working at all either lights on or off. Initially I thought this was CIM related however now im less convinced.

After poking around with a multi meter there definitely is nothing reaching the horns, however there is a definite relay clicking in the UEC. After further investigation Ive narrowed it down to a relay that was under the additional cover, specifically the one with "742 355-01" poking the 2 pins on the back with a multi meter shows a definite 12V when the horn is activated however there is nothing on the output side of the relay.



Is it possible to replace just this circuit board part of the UEC or am I looking at a whole new UEC. Or are there any other possibilities as to what could cause this?

Also in terms of replacing it presumably it would need to be unpaired from the donor car then repaired with mine, I do have an unmentionable diagnostic device however I dont have the best of confidence in it tbh so would probably look for someone locally with Tech 2 if thats whats required.

[pecky]

That circuit is the brains of the UEC, so swapping that is basically the same as swapping the UEC

All horn issues I've come across are CIM related, but your investigations may well back up your thoughts.

It will need to be programmed to start the car, but if you just fit another one it should let the horn work if that indeed is your issue. You then know if it is worth getting it programmed in or not.

[domtorredo]

Did you checked horn itself or if voltage goes to horn?

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[sean-tek]

Thanks Pecky,

Yes that relay above is 100% clicking every time the horn is pressed yet there is definitely nothing on the output side although I can only meter the solder point which to be fair looks like it could possibly be a dry joint . I assume if it was CIM related then the relay wouldn't energise when the horn was pressed?

Im tempted to desolder it and replace it or just reflow the solder on the current one. however my initial searching brings up no results for the number on the relay. Dont suppose you would know a source I could get one form or equivalent?

I guess I could get a donor UEC and remove it from that although tbh id rather just get hold of the relay if possible.

As a rough guide could you give me a ball park figure of what Id expect to pay for someone to Tech 2 a UEC if I need to?

Also if I do have to source one are all astra H UEC's created equally or do I need to specifically find a VXR one?

@domtorredo yep disconnected the horns and attached a multi meter to each one neither got any voltage which also fits with the output side of the relay showing 0V

[domtorredo]

So relay clicks meaning voltage is applied to coil, and relay works but it doesnt mean its ok.
Was there 12v on input side i think it was permanent or switched but in any way it should be there with ignition on, when you will dissamble uec you will find bars and pins only soldered piece is that pcb
If you want can check wiring so if its permanent than uec can be rulled out to be faulty

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[domtorredo]

Ah and relay must be 4 pin or leg
Coil circuit 2 legs and pass thrue circuit 2 legs

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[sean-tek]

So yes the coil side of the relay is energised and clicks when the horn is pressed and clicks again when the horn is released proving at east the coil of the relay is energising properly, however there is absolutely nothing on the output (pass thru) side of the relay whilst the coil is energised. I suspect looking at it it's because of a dry solder joint where the output side is soldered to the PCB however I would really like to source a replacement relay but am struggling to find that exact one anywhere.

[domtorredo]

Lets put coil side away for now
That should leave you a 2 pins from which 1 must be positive all a time if its not than problem wont be in relay

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[sean-tek]

Very valid point, hadn't thought about that so I need to meter between one of those output pins and earth and should have a permanent 12V. It's dark now but will test again tomorrow

[sean-tek]

also anyone clued up on hella part numbers, if it does turn out to be the relay is this a close enough match to work? original part number currently fitted it 4RD-742-355-01 the below is 4RD-742-355-22

both are 12 v relays with the same pin out from what i can tell

http://www.ebay.co.uk/itm/1pc-Cruze-...-/181612562319