Central Locking Troubleshooting - Pt2

[maelgwn]

Hi guys

Hoping for some advice about what to try next with my central locking.

Symptoms are:

Back passengers doors do not lock with the key. They do lock with the button on the drivers door and unlock as expected.

Back doors and boot do not show up as open on the dash when they are open.

Front doors work fine.

I have pulled the locks out of both back doors - checked and repaired wiring harnesses where needed, and checked the microswitches in the locks and they we all ok. The only thing out of the ordinary was the voltage at the solenoids seemed a bit low (only got to about 9V when pressing lock button and tested through my multimeter).

So, what should I try next? Do I need a VCDS to test the Central Electrics Control Module?

[Idle]

Hi guys

Hoping for some advice about what to try next with my central locking.

Symptoms are:
(only got to about 9V when pressing lock button and tested through my multimeter).

So, what should I try next? Do I need a VCDS to test the Central Electrics Control Module?

9V looks pretty low — I'd expect to see something approaching 11 or more.

Try it with the engine running and see if it comes up — if so it might be battery.

Otherwise look for resistance somewhere (corroded contact(s) — partly broken wire — something loose — bad earth etc.)

[vdubmotorworx]

As above...9v is no good. Sounds like resistance issue.

[piper26]

Your description of symptoms leads to door lock units as you are not reading the latch open or closed signl. A dtc check will give you an idea of what is going on. Reading the measured values from the door module would give a better overview of what is happening.

[maelgwn]

Thanks guys - voltage drop is a good thought - doesn't explain the latch open/closed? Where should I be looking for it?

Checked the voltage at the fuse box when locking/unlocking - that is ok.

I think there should be a ground connection in the lower B pillar - i guess I could check that however would not account for both locks not working.

Are there other connectors for power between the engine bay fusebox and the B pillar?

Your description of symptoms leads to door lock units as you are not reading the latch open or closed signl. A dtc check will give you an idea of what is going on. Reading the measured values from the door module would give a better overview of what is happening.

No relevant codes are thrown. Don't have the technology to test the modules through the canbus however.

[piper26]

Which module have you scanned for codes?? Does anything come up within rear door electronics or have you only scanned central electrics?

It is interesting how you say it will lock on one signal but not the other.

[piper26]

You also stated you repaired wiring harnesses where needed?? Which wires did you have to repair. The repair may be your resistance if not a 'clean' repair.

Just an observation from your original post. Especially when you seem to be experiencing some voltage drop possibly

[maelgwn]

Which module have you scanned for codes?? Does anything come up within rear door electronics or have you only scanned central electrics?

Just central electrics - it does show codes from the door modules if they are disconnected etc.

It is interesting how you say it will lock on one signal but not the other.

There are two types of 'locked'. If you press the button on the door - you cannot get in from the outside but you can still get out. If you lock with the key - it is effectively deadlocked, you cannot open the door from the inside or the outside. Yes - this could be the Voltage drop issue - enough power to move the lock, but not enough power to move the lock and solenoid for deadlocking at the same time?

You also stated you repaired wiring harnesses where needed?? Which wires did you have to repair. The repair may be your resistance if not a 'clean' repair.

Just an observation from your original post. Especially when you seem to be experiencing some voltage drop possibly

Wiring harness replaced in rear left door, just some electrical tape added where insulation was started to break in rear right door. As the behaviour of the doors is the same, seem unlikely to be this.

Thanks for your help.

[piper26]

Yes central electrics will show some faults however you can interrogate the actual door module for a more detailed view.
I am aware of deadlock but is that what the concern is or not locking at all with the key. The lock units actually have a seperate actuator for deadlock.
These lock units are very common. If your car hasn't had them yet then there is a very high chance that the safe motor has failed.

The voltage reading you are getting is it after latch (I.e earth side or the supply to the lock. Also what multimeter are you using. A multimeter is usually not quick enough to register the signal at its full strength. Hence why we use oscilloscopes to diagnose electrical faults

[maelgwn]

Yes central electrics will show some faults however you can interrogate the actual door module for a more detailed view.
I am aware of deadlock but is that what the concern is or not locking at all with the key. The lock units actually have a separate actuator for deadlock.
These lock units are very common. If your car hasn't had them yet then there is a very high chance that the safe motor has failed.

I might need to get a VCDS to interrogate the door modules in a more comprehensive fashion.

Does not lock at all with the key. Tested the safe motor on one lock straight onto the battery and it works. Can hear the motor 'whirring' inside the lock when you press the key.

The voltage reading you are getting is it after latch (I.e earth side or the supply to the lock. Also what multimeter are you using. A multimeter is usually not quick enough to register the signal at its full strength. Hence why we use oscilloscopes to diagnose electrical faults

I think I measured it at the connector to the lock.
Normal **** Smith multimeter - I did wonder if the sampling/display frequency was high enough, sounds like it might not really be showing anything then? A scope is out of the price range for me, don't mess with this stuff enough to buy one.