W202 Green and red alarm lights flashing together simultaneously - solved

[cazyp]

Hope this will help someone else as on searching there's a few contradictory threads. This car W202 1996 C36.

On locking last night the mirror and door green and red lights flashed together at the same time. Unlocked the car, got back in and the mirror lights continued to flash.
Tried to start it out of curiosity but it would turn over without firing - immobilized.

Locked car and went to bed. Green and Red still flashing together when locked.

Went out this morning and unlocked (still flashing together) and tried the sit in car, double click the key fob the insert and start within 30 seconds. Worked, car started but the mirror lights still flashed and the ABS and brake pad low warning lights were on. Bugger.

Locked it up, walked to the shop and bought 2 x CR2025 batteries for the key fob.
Replaced them. Unlocked car, lights flashed still together. Sat in car locked then unlocked and held button on fob down for 5 seconds the into ignition. Car started. No ABS or brake warning lights displayed. Drove round the block because its a C36 and fun to drive.
Got home, locked up and yes, just the wonderful sight of the one flashing red 'locked' LED in the door and on mirror.

All is well again. So simultaneous flashing of door and mirror LEDs = dying key fob battery.

Work noting that a red flash could still be seen from the IR bit on the key fob and purple flashes on camera phone - so thats a rubbish test for battery strength..!

Hope that helps someone.

 

[121stjohn]

I have also had this on my w210 and after much scratching of head; discovered that the boot sensor in the lid was wet through due to ingress into the lid(still trying to solve that one!) once the switch was dried the lights (red green) behaved correctly...I believe it to be this as it has happened a couple of times...

 

[BTB 500]

So simultaneous flashing of door and mirror LEDs = dying key fob battery.

This is standard on most M-Bs of that era (certainly my SL), and is mentioned in the handbook. But useful info. if you don't have one.