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350matt, Engineer
Category: Mazda
Satisfied Customers: 21724
Experience:  Mechanical Engineer BEng Hons22 years experience
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Have a 2003 mazda 6. 2.3liter just replaced alt. Have a good

Customer Question

Have a 2003 mazda 6. 2.3liter just replaced alt. Have a good battery but its being drained and now sec. Immobilized. Can't figure it out.
Submitted: 1 year ago.
Category: Mazda
Expert:  Amedee replied 1 year ago.

Hello and welcome! My name is ***** ***** I can assist you with your question. Would you like to know how to check for a battery draw?

Customer: replied 1 year ago.
Immobilized won't start with key
Expert:  350matt replied 1 year ago.


if its really low on battery voltage then this will immobilise the car so I'd 1st suggest charging the battery up

then once you can start the car again you then I'd first check the easy things like is the boot light or any other interior light staying on then check that the main battery connections are tight and in good condition also check the earth strap to the engine / gearbox.

Next I'd check the current drain aspect, the best way to find what circuit is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable.

A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next.

Once you've isolated the circuit with the excessive drain check the wiring connections and plugs to components and the wiring harness that runs by the engine bay fuse box - the wiring harness chaffs / rubs through and gets damaged - but its not always easy to see so be careful when checking..

Also check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright.

if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement

And one last thing is – how old is the battery? – As even good quality ones need replacing every 5 years and faulty battery just won’t hold a charge

Customer: replied 1 year ago.
This is not about the battery it's about the emmobileizer
Expert:  350matt replied 1 year ago.


if you read my answer I state that the battery must be charged to allow the immobilser to function correctly?

So please try charging the battery as the 1st step

Customer: replied 1 year ago.
The battery has a full charge
Expert:  350matt replied 1 year ago.


if the battery is fully charged and you can't get the immboliser to disarm the next step is to replace the battery in the key fob and if that doens't help then try resetting the ECU by disconnecting the battery cables and clamping them together for 10 mins.Remove both battery leads from the battery then use a nut and bolt or G-clamp to hold both battery lead terminals together.

This discharges any capacitors / memory within the ECU and around the car so ensures all memory settings are wiped clear - back to the factory default.

This will reset all the systems on the car and you may need the radio security code to get it going again, and ensure that the keys are in your hand when you re-connect thebattery as the car may lock and turn on the alarm

Expert:  350matt replied 1 year ago.


do you still need help?

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