Support Added for the Lucas 5AS Immobiliser

Download Link: https://andrewrevill.co.uk/Downloads/MEMS3Tools.zip

As of Version 7.91, MEMS3 Mapper now supports the Lucas 5AS immobiliser.

Having recently added support for the earlier families of MEMS ECUs, I decided for completeness would add support for the Lucas 5AS immobiliser. Some years ago, I did a lot of work deciphering the internals of this immobiliser, but I didn’t get around to working out the communications protocols it uses. Now, armed with the knowledge gained from work on the ECUs and helped by work done by James Portman at rovermems.com, I decided I was in a position to do a proper job of supporting the immobiliser to the same level as the ECU families.

One of the most useful features available is the ability to PAIR KEY FOBS WITH THE IMMOBILISER.

The Lucas 5AS Tools Application

You can simply select the Lucas 5AS Immobiliser from the list of ECU families:

This pops up what looks like a regular dialog box, but it’s actually a separate application that supports the immobiliser rather than engine ECUs. You will see there are now two application icons on the taskbar. You can run this application on its own it you want. In the root folder of the MEMS3 Tools installation there’s a launcher file Lucas 5AS Tools - For Lucas 5AS Immobilisers Only.exe which you can double-click to launch it as a standalone application.

It’s written in very much the same style as the other applications in my MEMS3 Tools suite, so if you’re used to MEMS3 Mapper or MEMS Flasher, you will find it all very familiar. If not, it’s very straightforward to find your way around. At the top of the window you can select the COM port or FTDI device which corresponds to your diagnostic cable (but see the section on Diagnostic Cable required below, as the requirements are slightly different to the other ECU families and you will need a slightly different cable for the Lucas 5AS immobiliser).

· The About 5AS button will connect to the 5AS and display the model name and serial number (where available – some features are only supported on Model Year 98 onwards units).

· The Read button enables you to read the setting memory from a 5AS, after which you can edit the various settings in the Fields tab:

· The Verify button allows you to compare the current project with the contents of the 5AS. This lets you check whether the file was read or written correctly (the messages sent between the PC and 5AS do not include any kind of checksum, so although they are generally reliable it’s always a good idea to verify).

· The Write button allows you to write modified settings back to a 5AS.

· The Save and Open buttons allow you to save 5AS projects to file, or open a previously saved project.

· The Hex tab lets you see the raw hexadecimal data read from the 5AS. You should not normally edit the data directly, but by changing settings in the Fields tab. The 5AS isn’t entirely tolerant of invalid data being written and it is possible to brick the units by writing data which it can’t understand:

· The Log tab shows the details of the communications between the PC and the 5AS. This can be helpful in diagnosing communications problems:

· The Live Diagnostics tab gives you live data from the 5AS. Click the Live Diagnostics button on this tab to start the live diagnostics running, then click Done when you’re finished. This includes some fairly static information such as serial number and Emergency Key Access (EKA) code, but also a live view of the various switch inputs the 5AS can see. There is also some live information about the key fobs, including the number of key presses it has detected from each of the key fobs paired. Note that these counts are only valid immediately after pressing a key fob button as the fields may be used for other purposes at other times, but it’s useful for testing key fobs for reliable operation. It also shows the code for the last key fob programmed, but again this is only valid immediately after programming.

· The Tools menu gives access to a few tools for maintaining the 5AS, namely:

o About 5AS – As described above.

o EKA Code – This reads the Emergency Key Access (EKA) code from the 5AS and displays instructions on how to use it. Note that if you want to CHANGE the EKA code, you should read the 5AS, edit the EKA in the Fields tab and write back to the 5AS:

o EMS Code – This reads the code sent to, and learned by, the MEMS ECU. If you want to want to replace the immobiliser without having to pair it again with the ECU, you can set the EMS code of the new immobiliser to match that of the old immobiliser and the ECU will see them as the same unit. The notes on CHANGING the EKA code above also apply to the EMS code:

o Test Outputs – This lets you force 5AS outputs ON or OFF for test purposes. In the example below the 5AS is being told to turn the immobiliser chime (in the Multifunction Unit of a Rover) and the horn relay ON and the immobiliser energiser coil OFF.

o Program Key Fobs – This allows you to program new or replacement key fobs into the 5AS:

§ Note that the programming procedure erases all keys currently paired, so you need to have all the keys you want paired to the 5AS handy before starting the process.

§ Press the LOCK button on each key fob repeatedly and steadily until the horn sounds. This will normally require 8 presses. If you’ve pressed the LOCK button more than 10 times and the horn still hasn’t sounded, the key fob is most likely faulty, the battery in the fob is flat, or the fob is not compatible with the 5AS unit. NB: On a Caterham the horn circuit is not connected to the 5AS unit, so it WILL NOT SOUND. There’s no harm in pressing the LOCK button more than 8 times. So, in this case I’d suggest pressing each LOCK button maybe 10 times for good measure, then testing the key fobs afterwards to make sure they paired correctly. If you waned to, you could connect a small bulb or 12V LED between the 12V supply and Pin 8 of the grey plug on the immobiliser; this will then flash briefly to represent the horn sounding.

§ When you’ve programmed all of the key fobs you want to use, click Done. You can program up to 4 key fobs into a single 5AS.

Diagnostic Cable Required

For the later MEMS ECU families, a cheap a readily available VAG COM KKL 409.1-style cable can be used. However, communications with the Lucas 5AS immobiliser are a little more complicated and it does require a special cable. I wanted to keep the requirements cheap and simple, so I’ve come up with a scheme that lets you convert a regular VAG COM KKL 409.1-style cable into a 5AS cable very quickly and cheaply. IF YOU DON’T WANT TO GET INVOLVED IN MODIFYING CABLES THEN JUST ASK ME – I’ll happily supply you with a suitable and cheap 5AS cable. The special requirements for the diagnostic cable are as follows:

· The Lucas 5AS uses both the regular K Line and the L Line for communications. These are both supported by KKL cables (which actually means “K, or K & L”) but the 5AS sends the data back on the L Line logically inverted. A regular KKL cable does not expect this and cannot read the data. There are two ways of converting the cable to accept inverted received (RXD) data, depending on the chip your cable uses, which will normally be an FT232R or a CH340G (the adverts for the cable usually specify which):

o If your cable contains a GENUINE FTDI FT232R chip, you can use the FT_PROG utility from FTDI here: https://ftdichip.com/utilities/#ft_prog. Click DEVICES, Scan & Parse to list the FTDI devices connected, identify the one which corresponds to your cable (if in doubt, unplug everything else) and then under Hardware Specific, Invert RS232 Signals check Invert RXD and then click DEVICES, Program. You should then completely unplug your cable and reconnect it to the PC to make the new setting take effect (until you do this it will continue to work as before, as the cable only loads these settings as it powers up).



WARNING: Most cheap Chinese cables containing FT232R chips are actually FAKE. The above will only work with GENUINE FTDI devices. FTDI at one point released drivers which deliberately and permanently disabled fake chips, and the fake chip manufacturers responded by making their chips read-only. This means they usually work for the purpose for which they were intended, but cannot be programmed as described above. It will appear to work, but if you read the cable again you will find that nothing has been set. If you’re buying a cable specially to use with the 5AS, I would recommend buying a cable with a CH340G chip and using the next option …

o If your cable contains a CH340G chip, you need to make one tiny modification. Find the CH340G chip and solder Pin 15 to Pin 16, as shown below. Note the small dot/indentation in the chip case which marks Pin 1. Pins 15 and 16 are opposite Pin 1. Make sure that Pin 15 is unconnected first. If Pin 15 appears to have a connection then you will need to desolder that pin and lift it clear of the board before soldering to Pin 16, but most boards I have seen leave Pin 15 unconnected.

· The Lucas 5AS immobiliser usually uses Pin 3 of the OBDII connector for K Line instead of the usual Pin 7. It uses Pin 1 for L Line instead of the usual Pin 15. This allows the immobiliser and ECU to be connected to the same OBDII connector. The KKL cable will be talking to Pin 7 and listening on Pin 15, instead of talking on Pin 3 and listening on Pin 1. The diagram below shows the female OBDII socket as fitted to the car, seen from the front (or the male OBDII plug as installed on a cable, seen from the wiring side):



The easiest way to fix this is to buy an OBDII extension cable of this design, which you can find for sale on eBay, Amazon and AliExpress:



The little secondary locking tabs one either side of the male connectors on these can easily be popped open as shown below:



This allows the terminals to be removed very easily by lifting the little plastic locating tangs with a needle or pin as shown below:



All you need to do is remove Pin 3 and Pin 7 and put them back in swapped over, and similarly remove Pin 1 and Pin 15 and put them back in swapped over. If you do this only on the white female connector on the end cable (not the one in the middle), then you have a two-port adapter; the black male connector plugs into your car, the middle white female connector is for the MEMS ECU cable and the end white female connector is for the 5AS cable. They should be labelled with permanent marker or similar each cable will only work in the appropriate port. You can use this to plug either cable into your car, or even both at the same time as they will not conflict: