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Mems3 diagnostic socket 
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Post Mems3 diagnostic socket
Hi all,

Does anyone know how the diagnostic socket for the mems3 / 5AS equipped engine is wired?

Mine has a red power wire, pink wire to the ecu and that’s it. It did have purple, orange and red/green wires that went to the 5AS unit but I ditched these when I found the 5AS unit was faulty so I did away with it and fitted a different immobiliser.

Does this socket need an earth?

I’m hoping to plug in an OSB2 code reader to see if it will tell me why my engine is in safe mode and limited to 5500rpm? it’s idling at 1200rpm also so it’s something to do with the VVC mechanism. At present the code reader won’t fire up?


Wed Oct 10, 2018 9:36 pm
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Post Re: Mems3 diagnostic socket
hi i have this

DESCRIPTION AND OPERATION
DIAGNOSTIC SOCKET
DESCRIPTION
General
The diagnostic socket is located immediately above the passenger compartment fuse box.
The socket is constructed to SAE directive J1962 standard and allows attachment of
TestBook, or any other SAE standard diagnostic tool, to the vehicle for fault diagnosis
checks.
OPERATION
Power supplies
Fusible link 1 (C0570) of the under bonnet fuse box supplies a permanent feed to fuse 12
(C0582) of the passenger compartment fuse box on a N wire. Fuse 12 supplies the power
feed from the passenger compartment fusebox (C0585) to the diagnostic socket (C0040) on
a P wire. The diagnostic socket (C0040) is earthed on a B wire connected to an earth point
(C0564) via the passenger compartment fuse box (C0584 and C0583).
General
The diagnostic socket (C0040) is connected with the following on K wires, which make up
the ISO 9141 K line bus:
 The ABS modulator (C0501).
 The EPAS ECU (C0316).
 The ECM (C0159).
The diagnostic socket (C0040) also communicates with:
 The airbag DCU (C0256) on a YK wire.
 The alarm ECU (C0061) on OU and RU wires.


Image

ANTI-THEFT ALARM AND CENTRAL DOOR LOCKING (CDL)
DESCRIPTION
General
The anti-theft alarm system monitors the vehicle and operates the alarm if unauthorised
entry is detected. The central door locking system provides local and remote means of
centrally locking and unlocking the doors. The anti-theft alarm system and the central door
locking system are both controlled by the alarm Electronic Control Unit (ECU) located on the
underside of the heater controls in the fascia. Active and/or passive engine immobilisation,
depending on market, is incorporated into the alarm ECU to prevent unauthorised starting
of the engine.
Anti-theft alarm system
The anti-theft alarm system operates in conjunction with the central door locking system and
is automatically armed and disarmed when the vehicle is locked and unlocked using either
the remote handset or the driver's door lock.
The main features of the system are:
 Perimetric protection that monitors the status of contact switches to detect
unauthorised opening of the bonnet, doors and boot lid. This feature arms with all
methods of door locking.
 Volumetric protection, where fitted, that uses a sensor, mounted under the rear
bulkhead finisher, to monitor for movement in the passenger compartment (with the
hood up or down). This feature arms only when the vehicle is locked with the remote
handset.
 Engine immobilisation that prevents operation of the starter motor and fuel pump
unless the system is disarmed by the remote handset.
 A red alarm Light Emitting Diode (LED) in the instrument pack.
 Indicator lamp flashing to provide visual confirmation of system arming and disarming.

Image

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Thu Oct 11, 2018 1:44 am
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Post Re: Mems3 diagnostic socket
That’s brilliant, thank you.

I obviously need to earth the socket. Hopefully it will work fine with just the power, earth and ECU feed.


Thu Oct 11, 2018 7:24 am
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Post Re: Mems3 diagnostic socket
I wired one in just the three wires live, earth and communication.


Thu Oct 11, 2018 12:32 pm
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Post Re: Mems3 diagnostic socket
I'll be having a diagnostic socket soon when I finally get around to installing the TF160 engine. I've kept the loom intact so hopefully all the right wires are there. If anyone has watched the latest episode of Project Binky they used a MG ZR loom for their mini conversion so it was interesting to see how they stripped back the loom - not looking forward to that job!

Re the limp mode - have you had the VVC mechs off? if not its hard to see how the timing of them could have gone out. I'd have thought that if you'd changed the cambelt and got the timing out you'd know about that from things other than the limp mode! Have you checked the camshaft position sensor or its associated wiring? I believe it is that sensor that reports to the ECU if the VVC's are miss-timed and that is what sets it into limp mode. I guess there may be other parameters that could do it too though.


Thu Oct 11, 2018 7:17 pm
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Post Re: Mems3 diagnostic socket
I did see the project binky i did that when i changed my engine
and I spent days looking at car plugs and socks
and pages of wireing diagrams

ImageImage

have you seen this
https://youtu.be/UM_w9VWZxwM

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Last edited by catsam on Fri Oct 12, 2018 9:50 am, edited 3 times in total.

Thu Oct 11, 2018 8:14 pm
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Post Re: Mems3 diagnostic socket
sanzomat wrote:
I'll be having a diagnostic socket soon when I finally get around to installing the TF160 engine. I've kept the loom intact so hopefully all the right wires are there. If anyone has watched the latest episode of Project Binky they used a MG ZR loom for their mini conversion so it was interesting to see how they stripped back the loom - not looking forward to that job!

Re the limp mode - have you had the VVC mechs off? if not its hard to see how the timing of them could have gone out. I'd have thought that if you'd changed the cambelt and got the timing out you'd know about that from things other than the limp mode! Have you checked the camshaft position sensor or its associated wiring? I believe it is that sensor that reports to the ECU if the VVC's are miss-timed and that is what sets it into limp mode. I guess there may be other parameters that could do it too though.



Hi Dave,

I used an MGZR engine loom for mine and it wasn’t too bad at all, it was quite therapeutic stripping out all the unwanted wiring!

I have a spreadsheet that will save you a load of time and anguish with it, let me know if you want a copy.

Regarding the safe mode, there are a few possible causes:

Electrical connections ( I’ve checked and it’s all wired correctly, have to check the voltage etc)
Sticky VVC mechanism - it’s a brand new HDU so I hope it’s ok though it could be sticky.
Problems with the VVC solonoids - I have to check the resistance on these
Dodgy cam position sensor - possible, it makes no difference to the 5500rpm limited if I disconnect?
Mid-timed VVC units - unlikely as the head was built by expert Roger Fabry (sabre)
Fried ECU circuits - hope not as it’s a new remapped Z & F jobbie
Possible ECU issue - I have deleted the 5AS and fitted a different immobiliser as it was faulty, could the ecu be looking for an 5AS to ‘learn’ and this is having an effect? I need to ask mark at Z & F

I’m hoping to see if I have any fault codes before pulling the cam cover off and checking the HDU is working with some compressed air.


Thu Oct 11, 2018 9:30 pm
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Post Re: Mems3 diagnostic socket
Its a while since I stripped a head but if I recall correctly the VVC timing can be confirmed by looking down the holes in the casting (with only the cam cover off, ladder still on) - if the holes line up then your static timing is good. I found I could operate a good HCU with a foot pump. My HCU was failing to turn the VVC link shaft and I found the fault was some bent teeth on the shaft gear where it interacts with the rack on the HCU. Pretty sure I left a picture on here somewhere back in late 2015/early 2016. I bought a replacement HCU thinking that was the problem but eventually traced it to the link shaft. I did all this before putting the engine in the car so never experienced the limp mode. It went straight to 7200 when it went in the car! I think I've got a good cam position sensor in the shed if you want to try that to exclude it from the diagnosis.

Yes to the spreadsheet please (although I've a vague recollection you may have already sent me it - I'll check!) What I'm not sure about is the difference between mems 2 and mems 3 where it joins the body loom. Also, the TF set up has two lambda but my current set up only has one. There is nowhere on my exhaust for the second one so hoping it won't get confused with the second connector open circuit (I guess worst case I could but a suitable resistor across the terminals that replicates a good setting)


Fri Oct 12, 2018 2:02 pm
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Post Re: Mems3 diagnostic socket
Have you got the VVC control plugs in the right sockets? Black plug sideways into the alloy Control Unit and brown plug down 'under' the cam cover vent hose.

I doubt it's the 5AS (or lack thereof) is it just stops the engine altogether by killing the fuel pump.

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Last edited by sidewinder on Fri Oct 12, 2018 2:13 pm, edited 1 time in total.

Fri Oct 12, 2018 2:05 pm
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Post Re: Mems3 diagnostic socket
Sanz - MEMS3, a missing post cat lambda will bring up a dual fault of missing sensor and failed heater circuit & have the MIL come on.

I don't have a cat so had a boss welded to the left side U bend to fit the 2nd Lambda and used a bypass module to give the ECU a signal that keeps it happy.

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Fri Oct 12, 2018 2:08 pm
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Post Re: Mems3 diagnostic socket
Hmm, I only have the one oxygen sensor in the manifold and just deleted the other.....I wonder if that would make a difference?

The car was like that originally but the engine loom was an MGF item with the second sensor left unplugged?


Fri Oct 12, 2018 2:25 pm
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Post Re: Mems3 diagnostic socket
The post cat sensor is only for the ECU to check the cat is working and maybe (I read somewhere I think) does very fine trim to the fuelling.

I ran my car with only primary one for years (with MIL LED disconnected) and never noticed it being 'limited'. I only fitted 2nd sensor recently cos I wanted the MIL to function properly and be able to warn of problem rather than just being on all the time due to missing sensor.

If you have a none standard ECU it prob has a function to not use the 2nd sensor anyway - ask the maker?

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Fri Oct 12, 2018 2:33 pm
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Post Re: Mems3 diagnostic socket
when I did my engine swape to mems3 i did not no what to do about the second sensor
so I just did not plug it in i have no mill light on and my car seems ok
the led comes on with the ignition and when the car is started the LED goes off

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Fri Oct 12, 2018 2:35 pm
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Post Re: Mems3 diagnostic socket
Thanks for the advice chaps.

My ECU was mapped by Z & F and I told him that I only run one sensor so I'm presuming all is ok there.

Looks like I need to wire an earth to pin 4 on the diagnostic plug so I'm going to do that first and see what it throws up. After that a treble check of the wiring (the plugs are definitely in the correct sequence), followed by checking the solenoid resistances and trying a second cam position sensor I have.

If its still doing it I'll take the cam cover off and check if the HCU unit is working correctly and look at the timing - I'd be surprised if timing is the issue though as Roger Fabry built the head and timed it up. Its an brand new HCU but I suppose it could be sticking??

Failing that it must be ECU related??


Sun Oct 14, 2018 7:48 am
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Post Re: Mems3 diagnostic socket
Attachment:
bent tooth on VVC shaft.jpg
bent tooth on VVC shaft.jpg [ 184.96 KiB | Viewed 58 times ]

This is what was stopping my VVC's operating correctly - slightly mashed tooth on the gear that is operated by the HCU rack. No idea how it could have happened but I guess one of those things you find on a second hand engine. Even with it like this I could get the HCU to turn the shaft with lots of pressure on the piston applied physically, but compressed air (and therefore probably oil pressure) wouldn't overcome the resistance the misaligned teeth were putting up. I probably could have filed the teeth back to straight but I found a perfect replacement shaft on ebay for £10. With the replacement shaft in the HCU would turn the shaft (and in turn the VVC's) with a puff of air from a tyre pump.

Another thing I read somewhere was that a bit too much sealant when re-assembling the cam ladder can ooze into the VVC shaft journals and make it bind.

Not saying that is what you have but if you run out of ideas might be worth checking.


Sun Oct 14, 2018 10:12 am
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