Mazda 626 GF gone crazy! Lock problems, diagnosing and fixing

Two interesting things found during diagnosing:
1. The instrument cluster is the one that unlocks the doors when you lock the car and there is an opened door.
2. Keyless entry unit is the one that re-locks the doors in 30 seconds, if the car never got opened.
00:00 Symptoms
03:10 Documentation
03:54 Keyless Entry Unit documentation
05:23 Door Lock Unit wiring diagram
06:55 Instrument Cluster wiring diagram
08:49 Key cylinder switches wiring diagram
10:19 Keyless Entry Unit wiring diagram
10:47 Door Lock Unit documentation
10:03 Liftgate opened signal wiring diagram
15:56 Sum up of what needs to be checked
17:22 Taking out the trunk bulb out
19:10 First BIG clue
20:06 Murphy is here
21:24 Second BIG clue
22:03 Third BIG clue
23:08 Testing the data line
31:04 Instrument cluster's role
32:57 How re-locking works
35:09 Almost found the issue
37:49 Very close!
38:13 I thought I found it!
39:50 Testing data line inside the door
41:55 Testing data ground line
43:47 Sanity check
45:51 Found it! A Head scratcher
48:15 New connector fixes the issue
48:50 Testing the new connector
50:23 Final test

[@elopezb86]

Great video!

[@NiksGMD]

This happened to me on my dad’s Ford Transit. Locked itself after unlocking it and when the driver door was opened, the locks were going crazy. The issue was a corroded wire from a bunch of wires coming from the driver’s door. Fixed the wire and now everything works fine.

[@Mazda626GF]

Yep, almost the same issue like mine!

[@Mazda626GF]

Interesting, maybe this is a weak spot of the 626. Only time will tell.

[@neilwalsh4058]

I have similar issue. Lock and unlock buttons on fob do sams thing , they both UNLOCK the car. I can car lock ok with actual key in both front door so not massive problem. Sounds like my keyless entry module is faulty?

[@Mazda626GF]

Is this a facelift? If so, measure the voltage on the blue cable going into the keyless entry unit. When locking, the voltage should drop in half, while when unlocking it should drop to 0V. It is a fast drop, so you will need a fast multimeter or an oscilloscope. On the pre-facelift, it should be the same, but I do not know the cable color. If the voltages are good, then the module is okay and the problem is elsewhere. It is best if you can actually perform this operation with the blue cable removed from the module (measure directly on the pin), as this is a common network between the keyless entry unit, instrument cluster, door lock unit and door cylinder switches, so if any of those are malfunctioning, or as in my case in the video, some corrosion on the door connector, you might get fooled.

[@neilwalsh4058]

@@Mazda626GF it's a 1999 so I guess that makes it a facelift? Rare car in UK now, they all seem to have disappeared

[@Mazda626GF]

@@neilwalsh4058 1999 is at the border. It could be either of these. You can actually tell by looking at pictures in on the internet - en.wikipedia.org/wiki/Mazda_Capella#Sixth_generation_(1997-2002)

[@romandirksen1700]

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