Mazda 3 2004 Central LOCK not working *SOLVED*

[Msmax]

Hi Guys,

Just like to share the solution if you find that LOCK does not work but UNLOCK do & v.v.

At first check that all door switches are operational:
- if all doors are closed then no DOOR OPEN indicator should be visible in the IC.
- open each door and verify that DOOR OPEN indicator pops up.

In my case when I pressed the LOCK button on one remote the nothing happened. Pressing LOCK on the second made the blinkers to switch ON.
Unlock button on first was dead but one the second remote it was OK. If all doors were locked by hand then UNLOCK would work.

1. First problem found the Door Lock of driver door had a broken lever so door open was never detected.
2. Both remotes did have loose soldering on the buttons
3. Last problem was a relay contact melted in the PJB (Passenger Junction Box) which is located under the dash,. above passenger foot space.

This relay is a special one: it has 2 relays built in one case.
One relay is used for LOCK and other for UNLOCK function.
Because the PCB is sandwiched you can not normally de-solder and replace the relay. So I cut the bad relay out the casing and glued an external relay to the board and wired it up.
Note that this relay must be able to handle at least 20A.

Tested in the car and all works fine.
See pictures attached.