Alarm system
Q My 2007 Honda Accord 2.2 CDTI has developed an annoying issue with its alarm system. For no apparent reason, usually late at night and much to my neighbours’ annoyance, the alarm sounder will operate, although the indicator flasher warning is not active. No amount of pressing the key-fob reset will stop the alarm. I tried disconnecting the main battery and it appeared to kill the alarm. I suspect there may be an issue with the alarm control module, which I believe is buried in the rear of the car, somewhere near the boot. I’ve also read that it could be the back-up battery failing in the alarm system.
The main battery seems to lose its charge occasionally if the car is left idle for 5-7 days, but I’m not sure if this is related to the alarm fault. Does the alarm module battery charge up from the main battery?
Dave Steele
A The first check is to ensure that the vehicle battery is in a good state and is not failing. A voltage drop overnight will produce a problem for the alarm system. As your battery does appear to lose charge over a number of days, this may be worth testing and replacing. It may be the case that a dead or sulphated cell in the battery is to blame. The alarm battery is charged from the vehicle systems, but it will never have been replaced and will now be around 14-years-old and possibly reaching the end of its useful life. The battery is actually a small pack of six button-cell batteries and should be the same as the one available here: https://bit.ly/cmkyabp.
This is not made to be a serviceable item and Honda advise replacing the complete alarm unit. Replacement of the battery will require the new pack to be soldered into place.
Once the alarm unit is extracted from vehicle’s rear offside inner wing, the casing can be removed from the unit to expose the PCB and battery pack. It is tricky but not impossible to access, although the interior rear boot trim will need to be removed. The battery pack costs around £8, but the unit itself should be checked for signs of corrosion or water damage before attempting to replace the batteries.
I then had a further update:
Over the weekend, I located the Bluetooth/hft module and did a test with a voltmeter and ammeter. With the module connected and the car locked on the key-fob system, the battery was discharging 0.21Amps.
With the Bluetooth/hft module disconnected under the same conditions the battery was discharging 0.02 amps. My battery was pretty well discharged when I did the test (12.2-12.4 volts), but I’ve now charged it up fully and left the Bluetooth/hft module out to see how it goes over the next few days.
I think this proves the faulty Bluetooth/hft module is the culprit of my flat battery. I fitted a new 7.2-volt battery in my alarm unit, as you recommended, and have had no issues with the siren going off since, even when the main battery was low on charge.
Can the Bluetooth/hft module be repaired if you can pinpoint the likely fault or is there a company in the UK who provides this service? I’ve found such a company in Dublin and I’ve emailed them for a price, but I thought there must be someone in the UK doing this as well? I’ve also looked at breakers and on ebay, but most sellers want £90-£100 for a unit which they cannot guarantee will work.
There seem to be several Bluetooth/hft modules used by Honda on various models, so I assume that they are not interchangeable? Dave Steele
There are variations in the hands-free talk (HFT) unit and I believe they are not interchangeable, so you would require the correct part number. The problem appears to be related to a £2 capacitor in the circuit, but it may only be possible to find such a unit by searching ebay. Being the largest component on the motherboard, the capacitor is quite easily spotted. It would depend on your proficiency with a soldering iron as to whether you felt able to attempt such a repair.
I did find one UK company that apparently can repair the module, http://bit.ly/cbnbtr, but I am unsure how much it would cost.