4200 driver's side door lock that doesn't

[todd.the.submariner]

Having read through every thread on SM and MaseratiLife looking for an answer, alas, a new thread must be born. Hoping that the hive mind can help me round this problem down or help with schematics and specs to support troubleshooting.

Background: minor heater hose leak (about 50ml, tops), but of course it dripped right onto the door lock/unlock ECU on the (US) Driver's side. Powered off the car, disconnected and dried out the connectors, reconnected. Module made an intermittent buzzing sound like a mosquito. Disconnected for a few days to ensure even drier... reconnected, buzz was gone. But so was my ability to lock/unlock the doors using the remote. Alarm would arm, but no door lock at all. No cycling of the locks shut/open. Nothing.

Made the bold assumption it was the door lock/unlock ECU part 184391. Purchased a Ferrari equivalent, installed, no change in symptoms.

Read through all of the forum entries for more ideas. Came across multiple threads about solenoids in the door locks, and using the key in the door vice the remote. ( I know... seems such a primitive act to have to mechanically lock/unlock a door). My symptoms didn't match any of those listed.

Driver's (US, so left) door: does not lock/unlock using the key. Nothing. If I cycle battery power with the disconnect switch, then when attempting to lock the first time with the key, I can hear the tapping of a relay in the door lock/unlock ECU but no resistance to turning the key, and no locking/unlocking. Tried this with the passenger door both locked and unlocked, no difference.

Passenger door. Locks and unlocks using the key with no problem, but does not force the Driver's door to follow, as one would expect.

Removed ECU connector and tested for grounded pins - didn't find any, but did find an oscillating voltage signal that sounded like the same tap-tap-tap interval that was heard in the above mentioned Driver's side step.

Does anyone have insight into the potential problem here? Or, if not, does anyone have pin diagrams and testing specs for each of the components, or know where I might find them? I have the test equipment, but would be "easter egging", in submariner speak, to try to blindly find the fault without some sort of drawing or pinout to follow.

 

[CatmanV2]

Was the replacement ECU new or used?

C

 

[todd.the.submariner]

Was the replacement ECU new or used?

C

It's a used Ferrari part.

 

[CatmanV2]

It's a used Ferrari part.

My thoughts are that it' possible that the replacement part is either non-compatible or faulty. I think you've done the correct thing. I've got no idea how the components communicate but I suspect that the ECU's are using the CANBUS and a wiring diagram is possibly not that useful. The solenoids in the doors just take a 12v signal as far as I know, so it shouldn't be beyond the wit of man to trace it back from the door jam connector and ensure that you've not somehow destroyed that.

C

 

[Oneball]

This is more of a question than statement of fact:

The key barrel is physically connected to the door lock with a rod. So if the key doesn’t lock or unlock the door and there’s no resistance to turning then there’s something mechanically wrong?

 

[CatmanV2]

This is more of a question than statement of fact:

The key barrel is physically connected to the door lock with a rod. So if the key doesn’t lock or unlock the door and there’s no resistance to turning then there’s something mechanically wrong?

That sir, is a very good point.

C

 

[davy83]

The other thing that might be worth a look, is there not a relay between the ECU and the locks? The locks use a bit of power I woudl be surprised if they are driven directly from the ECU, its possible. I will try to find the wiring diagram for the locking system (assuming 3200 and 4200 share the same door locks?)

 

[todd.the.submariner]

The other thing that might be worth a look, is there not a relay between the ECU and the locks? The locks use a bit of power I woudl be surprised if they are driven directly from the ECU, its possible. I will try to find the wiring diagram for the locking system (assuming 3200 and 4200 share the same door locks?)

I found the feeder fuse to be #44. It’s intact, never blew.


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[todd.the.submariner]

That sir, is a very good point.

C

As a manager of tradesmen, particularly mechanical and electrical trades, there was often a comical passing of blame for equipment faults.
Referring to the old song, my mechanics would shift blame to the electricians with a skill called The Electric Slide. “It’s Electric” . If you’re under 40, YouTube it.

The fact that it could be a mechanical problem hadn’t even entered my mind. My mechanics trained me well.

Happy to give that a try in the morning. Any tips or tricks relating to door lock disassembly I should know? Or will my rudimentary skills gained on 60s muscle cars be sufficient?


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[CatmanV2]

There's a very detailed how to on door card removal. It's not hard at all.

We don't do the 'It's Electric'. Because I'm in operations, it's always my fault....

C

 

[todd.the.submariner]

There's a very detailed how to on door card removal. It's not hard at all.

We don't do the 'It's Electric'. Because I'm in operations, it's always my fault....

C

I feel your pain, sir. As I too have risen above the individual trades to the place where the tree narrows.

Will first try an electric shortcut to toggle the solenoid manually. Having a hard time believing it to be solely mechanical as I don’t hear the driver door solenoid cycling when using the remote lock feature, or when cycling the passenger door manually.

But I’ll then follow the Sherlock Holmes rule of eliminating the unlikely. Will undoubtedly learn something along the way. Already learned that a door panel is referred to as a “card” by our friends across the pond.


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[2b1ask1]

Already learned that a door panel is referred to as a “card” by our friends across the pond.

Yep, to us the panel is the metal skin on the outside, hence panel gaps.


Hope you get it sorted, I have non-functional locking at the moment, will be replacing the locks when I get the time (had the parts for 8 months) and if not resolved I will then be replacing the module under the dash but I fear that as the likely culprit for the module failure is actually a blown heater matrix dripping on it!

 

[davy83]

I found the feeder fuse to be #44. It’s intact, never blew.


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was not thinking of a fuse so much as a relay somewhere? These cars are getting old and relays dont last forever, if the relay got wet it would not do it any good!!!!

 

[todd.the.submariner]

The mystery deepens, and the tradesman answers are both correct. It’s mechanical, AND electric.
This evening, had the pleasure of removing the drivers side door card using Loz’s guide. And plain as day, the drivers side exterior key tumbler’s linkage was dangling free.

Being a man with large, ahem, hands... it was a bit of a comic challenge to snap it back on, but I managed by using a large screwdriver through the round access port.


Happy to have found such an obvious fault, it was time to retest. A partial success. The drivers door key now locks and unlocks the door, but the remote still does not work. Also, the doors do not synchronize their locking and unlocking actions. They attempt to, but cannot complete the action. And sometimes they don’t attempt to. I spent a good five minutes looking the part of a mixing DJ, reaching across the cabin to cycle port and starboard locks together, then apart, then opposite each other.

So, still some work to do.
One clear symptom. If I lock the drivers side door from the inside, then cycle the passenger side lock, the drivers door will half unlock. That’s the only consistent test result. Nothing makes the passenger side unlock electrically.

One additional history detail. My locks and alarm modules were all replaced a few months back by the local Maserati dealer. Long story, but the dealer could not produce a second key for me after multiple attempts due to a records mismatch, so all key related parts were replaced so that I’d have a full set of keys.

I would wager a small confection that their work introduced the mechanical lock problem just corrected, but I can’t see how the electrical problem could have been their fault as the locks worked fine for months.
Calling it a day (Chartreuse, lime, and local gin calling my name), but will sally forth again tomorrow after work.

Any other diagnostic ideas out there to round this down to a component?

 

[2b1ask1]

A simple one to try is a battery reset, 10 mins with the isolator off and the locks both on unlocked.

 

[CatmanV2]

So things do break at the same time. How odd!

I think Newton has the right of it for now.

Which side ECU did you replace?

C

 

[todd.the.submariner]

A simple one to try is a battery reset, 10 mins with the isolator off and the locks both on unlocked.

Excellent idea for a baseline. Will try that first thing in the morning.


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[todd.the.submariner]

So things do break at the same time. How odd!

I think Newton has the right of it for now.

Which side ECU did you replace?

C

The mechanical fault was probably there ever since the lock replacement by the dealer. I hadn’t used a key in the door since purchasing the car. The electronic fault was likely caused by the small heater leak. That’s what prompted this investigation, which then uncovered the mechanical fault.

Will try a power off/on in the morning. Though on reflection I’ve done that every time I work under the dash as I find the door open chime tiresome. But will try it again for good measure.

As for the ECU replaced, I replaced the door lock control, which is a single ECU strategically placed directly beneath the heater core hose connections. The dealers work extent I’ll have to pull from the records tomorrow.


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[todd.the.submariner]

Recovered from track day and tilting at the windmill once again. Cleaned all contacts and tried alternate door lock/unlock ECUs

On installing ECU, door lock command was executed perfectly. Once. Never again. Door unlock command from remote also had no effect.

Locking from inside the doors:
Locking passenger side, the driver side would lock, partway. Lock cycled but the door lock switch only moved slightly. ECU audibly clicked once per second until I manually moved the drivers side door lock switch to match the passenger side.

Unlock command from passenger door switch was ignored by drivers door, ECU clicking as before until mismatch resolved. Drivers side door lock similar: it’s lock and unlock commands were ignored by the passenger door, and ECU clicked until locks were aligned.

Conclusions so far:

• the ECU isn’t the problem. Symptoms didn’t change with ECU replacement .
• locks are mechanically sound, operating smoothly with key and switch
• lock position sensors are operating correctly, as the ECU is consistent in its complaints about mismatch
• motorized lock/ unlock commands appear to be the problem

Confusing bits

• remote lock/unlock doesn’t work on either door.
• neither lock gets commanded successfully to its previous position when there’s a mismatch, though it sounds like the ECU is certainly trying to do so.
• one time, on replacing the ECU, both locks cycled to locked with a remote command, so the electrical locking mechanism isn’t fully broken.

Few things are as fun to chase as intermittent or inconsistent faults!


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[CatmanV2]

I reckon you've got one or two failed lock modules


C