Central locking and parasitic battery drain

Technical Area Electrics & ICE
2

Hi!

I was hopefully looking for some advice and guidance on a problem we have with my wife’s 2007 MX5.

The central locking does not work either with the key fob or using the key in the door. I have also identified a parasitic drain (approx 250mA) on the battery which I have (so far) isolated to the ‘ROOM’ fused circuit. 

I have looked at the wiring diagrams sourced from http://www.mellens.net/mazda/index.html and notice that the ROOM circuit also feeds into the ‘Keyless Control Module’

Would I be right in thinking that the two problems are somehow linked and does anybody have any ideas on the best way forward to resolve the issue(s)

Thanks in advance

Adrian

3

I’m not trying to put you down, but the word ‘parasitic’ is incorrectly used - it means a parasite (a bug)
is present in the car. While the word ‘bug’ is often use to describe faults in computer software, the more correct term is ‘fault’ when applied to electric circuits.

So this invokes a question - Are you checking with the ignition on, or off? If the ignition switch is on, then there will of course be a perceptible drain on the battery. If it’s off, are you checking with a door open? - The normal internal light will be on.

If you have disconnected the Positive lead to the battery, and reading current flow between it and the battery positive terminal, under the following conditions, then the reading you have would either be right, or wrong. One point - if you open the boot to do this, then does your boot light come on, or do you have to switch the parking lights on for it to work? If it comes on without doing this, then you may also read the drain from that light, under any circumstances.

1) Ignition off. Alarm and immobiliser set - these have a constant battery drain under this condition, that is normally around 0.2 amp (200 m/a) The ECU also has a back-up battery, used to retain variable settings, and if that starts losing it’s charge then it will also load the ‘Dark current’. This condition is normal.
Note - Dark current is in fact a misnomer, it actually means internal resistance inside the battery, from which most batteries suffer at some point in their life.This result in an internal current which over time can result in a flat battery.However, the term ‘dark’ is often used to describe the constant external drain on a battery, when apparently, everything is off. This overlooks the fact that when the car is locked and alarmed, the conditions as outlined above are still active.

2) Ignition switch off, alarm and immobiliser deactivated . Boot light on? Car door(s) open? - interior light on. Either of these conditions will show a battery drain current.

3) Ignition switch on, but engine not running - the ECU is ‘live’, so is the ignition circuit, petrol pump etc. Any current drain will be larger than 250 m/a. I don’t know if this will affect the igniter coils on a Mk3, I do know on older cars it can result in a burned out coil if left on for a period of time.
Presumably your comment isn’t about this condition.

Last - Unfortunately I don’t have a wiring manual for a Mk3, so I’m unaware of any potential faults in the door locking circuits, as far as I’m aware they operate on a pulse signal rather that a prolonged one, as you might expect with a motor driven device.* I would suspect a blown fuse, but I can’t point a way to that possibility. Another possibility is you have an earth fault on that circuit, either on the live side, or the negative (earth) connection is open . A live going to earth would show a greater current flow than 250 m/a.- and blow a fuse. On my car (an NBFL) you can still lock the doors with the ignition key, without using the fob, but I’m not sure you can set ‘double locking’ by turning the key twice.- You could on some other cars.
An inactive fob could mean a flat battery inside, but if you can’t lock the doors with the ignition key then I have no idea what the fault might be - without a wiring diagram to look at.

I’ve just checked my NB manual, and the 10 amp ROOM fuse is in the immobiliser circuit, but the power door locking system is on a separate 10 amp fuse marked D.LOCK.- have you got a D.LOCK fuse in the fuse box? If so, is it O/K?

  • note (added* I could be wrong on the motor driven device, as my NB manual shows a motor for each power door lock.

However I made this assumption on the fact that there’s no sound of a driving motor, just a ‘clunk’ as the doors lock. On my sones Merc, which also has power door locking, one motor can run for several seconds as that mechanism appears to be in need of attention, though it does eventually lock. 

4

Gerryn

Thanks for your prompt and comprehensive reply

I take your point on the use of the word parasite and stand corrected - no offence taken.

I am checking the current with the doors unlocked, closed and Ignition switched off, the keys were in my pocket (alarm and immobiliser deactivated?), interior and boot lights OFF (at the switches), when I pull the ROOM fuse the current drops off the scale on the meter. The ROOM fuse is 15A.

If I start the car with the ROOM fuse out, among other things the ‘check engine light’ is on and the radio/CD player had no power.

WRT the central locking… I can lock/unlock the driver’s door with the key but have to lock/unlock the passenger door manually (from the inside), there is no motor or solenoid activity when locking or unlocking with the key. I confess I didn’t specifically checked for a blown D.LOCK fuse but I had checked all the fuses as I pulled them when tracing the source of the current drain, they were all good. I have tried both key fobs, but have not checked or changed the battery in either one.

Hope this helps

Adrian

5

Comments in red, no intent to make it look like I’m mad! I would have used blue, but it looks like black on my PC.

 

6

A more accurate term would be IOD,ignition off draw.What test equipment are you using for checking the Iod?Most modern cars have a "settle time"before everything shuts down,so I would allow at least 30 mins before making an accurate assessment of current being drawn.I would suggest you need to address the Cdl fault first ,this may be related to your problem.

7

Sorry - but I disagree with all of that, there is no ‘settle down time’ Granted if there’s a capacitor anywhere still connected directly (via a  fuse) to the battery then it may draw a charge for a short time, but nowhere like 30 mins. If that particular component has a feed from one or any the other fuses mentioned in the OP’s post then he took them all out. A charged capacitor will discharge through it’s associated circuit, so if disconnected, it will discharge in seconds, not minutes,

Any component with a coil - relays, motors etc, will generate a back EMF when switched off, Mazda aren’t stupid, most coiled components have a diode shunt across them to cancel that out. You can’t read that by sticking an ammeter in series with the Positive battery cable and the Positive terminal of the battery. These components are also switched off by removing the fuse, so same as just said.

While my manual - and car relates to an NBFL, Mazda don’t change basic wiring. and further reference to my manual says the ECU (correct term PCM) is also supplied from the ROOM fuse - among several other components. No reference voltage to the PCM will I imagine, automatically register as an Engine fault, which the PCM will signal to the engine management light - simple.

If I had a NC wiring manual, then it would be easier to point at any possible problem area, but I don’t - so it’s only by reference to an earlier manual that I can make any comments.

 

8

 

According to the Wiring.pdf for the NC on the Mellens web site, the Room Fuse supplies the following circuits (via the Blue/Red wires), but some bits might not be fitted on some cars.

 Climate Control Unit

 Instrument Cluster computer

 Steering Angle sensor in steering column

 Ignition Key Led

 Key Reminder Switch

 Keyless control module. Do you have keyless control? ie no igntion keyhole on steering column? If not then this module not fitted.

 Keyless Receiver

 OBDII Connector

 PCM (Powertrain Control Module), left front corner in engine compartment

 Map light

 Boot Light

 Boot Lid relay

 Power Retractable Hard Top Module

 Audio Unit

 TCM (Transmission Control Module, Auto)

 

I would suspect a light switch with some water damage, eg the door switch or boot switch, or maybe the boot relay has been water damaged. 

And you didn’t leave anything plugged into the OBDII connector?

Good luck

9
10

Richard - so immobiliser not on the ROOM fuse with the NC? I’m not surprised the fuse has been upped to 15 amp - that’s a fair load on it, especially when fully equipped.

Is there a door lock timer on the NC? - could that be faulty?

11

 

Good question.

My memory has just kicked in (still dopey at the moment because of painkillers) when you mentioned timer and this has come up before.  Below is a quote from what I found out a fortnight ago on another thread.

https://www.mx5oc.co.uk/forum/yaf_postsm628213_Flattening-Batteries.aspx#post628213

According to the Mazda manual for the NC, one should measure the residual current with the ignition off, all doors closed all lights etc. off. Initially the residual, dark, parasitic current might be as high as 300mA after the engine is switched off. Wait for about half an hour when the dark current should now be 25 -45 mA; 45 when the security LED is lit, 25 when it is not.  If a door is opened or anything switched on it is back to the 300mA for a while again.

 

12

O/K - that confirms what missfire said, but that doesn’t happen on my NB. Also - it’s not about the door lock timer, so your painkillers must be good! I hope they aren’t the ones mentioned recently, which name I forget, but apparently can cause heart problems. The door lock timer on my NB has everything related to the doors and the immobiliser connected to it, so that’s why I mentioned it.

Apologies to missfire BTW.

13

May I chirp in with what I’ve learned about the central locking.

 

The key fob has a red light in the centre. Between the sets of buttons is a white insert. This should illuminate red when a button is pressed.

This will at least tell you if the batteries are flat.

 

If you operate the lever from inside the cab, then the drivers side lever should operate both sides of the cars central locking.

However, operating the passenger side lever IIRC only operates the passenger side lock.

 

So it could be a long shot, but if you have a combination of flat batteries and a faulty drivers side actuator then I could imagine why the central locking appears not to be working.

14

Frankly, while on the face of it you present what seems a logical argument, the last sentence invalidates any thing you said - If the main Battery is flat - the central locking cannot work. If the drivers door actuator is faulty, then even with a fully charged battery, it won’t work either. The passenger side will still work though. Combining the two negatives doesn’t make a positive! At the moment - assuming a Mk3 still has a door lock timer, then I reckon that could be faulty, as everthing to do with locking goes through it. As you appear to have a Mk3, try this -

Lock the car, and after the lights flash - showing the system is now armed, turn it off, but don’t open the doors. After a delay (around 30 seconds) the system should relock the doors and arm the alarm. If this happens, then the car is still fitted with the door lock timer. If it doesn’t re-lock, then It isn’t.

This may help locate the problem IMHO.

15

Frankly, while on the face of it you present what seems a logical argument, the last sentence invalidates any thing you said - If the main Battery is flat - the central locking cannot work. If the drivers door actuator is faulty, then even with a fully charged battery, it won’t work either. The passenger side will still work though. Combining the two negatives doesn’t make a positive! At the moment - assuming a Mk3 still has a door lock timer, then I reckon that could be faulty, as everthing to do with locking goes through it. As you appear to have a Mk3, try this -

Lock the car, and after the lights flash - showing the system is now armed, turn it off, but don’t open the doors. After a delay (around 30 seconds) the system should relock the doors and arm the alarm. If this happens, then the car is still fitted with the door lock timer. If it doesn’t re-lock, then It isn’t.

This may help locate the problem IMHO.

In earlier days, I wondered why Mazda did this, then it occurred to me, the locking and alarm system works off a pulse, and if the car were to get a spurious pulse on the same frequency from elsewhere than the fob, then the car would turn to an active (open) state, so the delay timer overcomes this. If the owner presses the fob, then he (or she) has around 30 seconds to get in the car, after that the system re-locks the doors and resets the alarm - and immobiliser.

16

Today’s efforts…

 Instrument Cluster computer - Unable to disconnect with my present level of access

 Steering Angle sensor in steering column - Disconnected - no change

 Ignition Key Led - Disconnected - no change

 Key Reminder Switch - Disconnected - no change

 OBDII Connector - checked - no change

 PCM (Powertrain Control Module), left front corner in engine compartment - not yet located

 Map light - Disconnected - no change

 Boot Light - Disconnected - no change

 Boot Lid relay - Disconnected - no change

 Audio Unit - Unable to disconnect with my present level of access

Also I removed the door cards from both sides and disconnected all visible plugs - No Change

So I’m slowly running out of options 



Any new ideas for me to try?

 

17

Adrian - Why are you going to so much trouble? None of what you’ve done has anything to do with door locking, and the ammeter reading you got was from NOT removing the ROOM fuse, for which it appears there’s a logical explanation for that - see Richards post above. You’ve also registered numerous faults on tbe ECU (PCM) which will remain till they’re cleared, and I doubt you can even start the car as it stands, you need to reconnect everything you disconnected and see if the car will start (engine warning light may come on, you’ll just have to ignore it) and take the car to the dealer if you can, or at least ring them if the car won’t start, and ask them if they can send someone to collect it.

As it stands ‘as is’ for now (no-one seems willing to confirm there is a door lock timer unit on the Mk3) so I can’t suggest that is the fault which causes the doors to not lock, but I suspect it may well be.

Either a dealer, or an experienced auto electrician can investigate, and confirm or refute this idea, but that’s as far as I can go on here - Sorry.

Don’t disconnect anything!

18

I think the current drain is normal for the car.  Don’t take stuff apart.

 

The door locks problem could be simply because of a damaged switch on the back of the key cylinder.

I assume the 20Amp Lock fuse is OK?

Check the switch module on the back of the key cylinder is not damaged.  It is a fiddle to get to but can be identified with the red sleeving on its small loom.

 

Then there is the control system.

Do you have the usual water leak from the grommets in the scuttle, dripping onto the passenger carpet, and also into some important circuits left of the glove box?

Here Gerryn’s post no2 is relevant.  I was wrong and the Advanced Keyless Control module still in there as an immobiliser but it is only partly populated with relevant wires.

 

Also be warned, the PCM is tied to the key and the receiving coil on the steering column; lose all the keys and new coil, key and PCM are required!

 

If you buy the ebay CD that was mentioned a couple of months ago it has most of the relevant stuff found on Mellens and a bit more including several pdfs of workshop manuals - but these are not complete for the cars and the wiring is a pain in Acrobat.  See my post 11 in the thread for how else to read it.

https://www.mx5oc.co.uk/forum/yaf_postst93981_MX5-workshop-manual-query.aspx