P38A Code P1668 - Anti Theft Alarm Serial Link Fault - Drive Cycle A

Hi Members,
I have recently changed the battery on my 4.6litre Yr2000 RR and resynced the key fob with the EKA code and routine. Connected up my BBS MSV2 Extreme diagnostics and found the above code (P1668). With the MSV2 I have accessed the BeCM and Motronic ECU and checked the Immobilsation codes and determined that they are the same, so that the two control modules synchronise. This has often been reported with the issue of key fob not synchronising.
All other settings have been checked, however when the car is "cranked over" there is no spark to the plugs...it is as if the immobiliser is still active. All fuses relays etc... have been checked fine, however, I understand that the "Crankshaft Speed & Position Sensor" could cause the "failure to start" as failure of this component does not necessarily record a fault, other than not starting and display various other electrical issuses.
Therefore ios ther any way of testing the "CSP Senor" and would this indicate the "Anti Theft Alarm Serial Fault" and what is the significance of the "Drive Cycle A" as the vehicle will not start. Any help appreciated....

If you have "Anti Theft Alarm Serial Fault" I'm pretty sure that would stop it starting so that should be the first thing to look at. I can test the crank position sensor, but then I have an oscilloscope, can you not see the CPS output on Faultmate. (I don't know the V8)

Thanks for the response and the BBS Extreme does outline any problems with the Crank Position Sensor and diagnostics, run through a series Crank Shaft Stages or Phases 1 to 4, which covers misfire detection and adaptation. In the log on the diagnostics these are indicated as "NOT DONE" in all 4 stages. On the same diagnostics page it also outlines that the immobiliser is "OK"......This would indicate all is perfectly functioning. However, as the CPS has not been recognise whilst cranking the engine over, could the CPS be at fault, by not generating a signal???

Fast Freddy said:

Thanks for the response and the BBS Extreme does outline any problems with the Crank Position Sensor and diagnostics, run through a series Crank Shaft Stages or Phases 1 to 4, which covers misfire detection and adaptation. In the log on the diagnostics these are indicated as "NOT DONE" in all 4 stages. On the same diagnostics page it also outlines that the immobiliser is "OK"......This would indicate all is perfectly functioning. However, as the CPS has not been recognise whilst cranking the engine over, could the CPS be at fault, by not generating a signal???

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It certainly could.

Thanks Datatek, for the reply and I assume that as no signal is being received by the BeCM Unit from the CPS, then the BeCM may outline the "Anti Theft Alarm Fault on Drive Cycle A".
From the LR Workshop Manual, Drive Cycle A commences from when the engine starts, see below. If the Immobiliser is apparently working and indicated as "OK" and enabling the engine to crank, I can only assume that it is the CPS at fault... fingers crossed ordered a new CPS and see if this rectifies the issue. Unless some other members have had the same issue and can shed some light....

Might have been worth checking the connector for corrosion before shelling out for a new one.

In the interim period whilst awaiting, I will check the connectors, but they are in a rather awkward location and as the weather here in blighty is some what cold and wet, doesnt lend itself to getting underneath and removing the part....but will keep you posted. Thanks again...

Fast Freddy said:

In the interim period whilst awaiting, I will check the connectors, but they are in a rather awkward location and as the weather here in blighty is some what cold and wet, doesnt lend itself to getting underneath and removing the part....but will keep you posted. Thanks again...

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If it makes you feel better, it's blowing a gale, freezing cold, raining and we are Orange alert for snow here

That does cheer me up some what and having said that just looked outside and its snowing, here in Lancashire already.....typical, just when you need your 4x4..... Time for a nice cup of tea and another log on the fire!

Update on progress.... a new Bosch CPS arrived today and was compared to the old unit. The old unit did show issues with resistance on a volt meter as well as checking on an oscilloscope. The new unit was installed and low and behold after disconnecting a HT Lead and placing a spare spark plug on the end, the engine was cranked and at last, the engine generated a spark.
The HT Lead, was reconnected and the engine cranked again.....no joy at all, other than the smell of Shell's finest.....I duly connected the MSV2 to establish any error on the BeCM and the Motronic ECU and their were none at all, in any sub sections.
I decided to remove a spark plug from the block and insert the spare one I used for testing. After re-cranking the engine, coughs and splutters started. I replaced four on one bank and re-cranked the engine, to the resounding resonance of an out of tune V8. I immediately replaced the remaining plugs and restarted the engine at the first turn of the ignition, the glorious noise of a happy engine. All is well now.
Moral of the issue, always check the spark plugs too, by removing them as they may get fouled up with carbon, as the ones I removed looked exceeding black and carboned up, perhaps the engine is or has been running a little rich.
The only issue I have now is a clicking noise from the alarm sounder under the fuse box, if anyone knows what this and how to cure it.....may be something to do when I lifted the fuse box up to check the underside???

The clicking from the alarm sounder, has been traced to a blown 5 amp fuse in position "Number 33" in the engine bay fuse box. This also feeds power to the OBD socket, which I didn't detect as I run the MSV2 from a mains adapter... Happy days all working and functioning as normal, just in time for the remains of the inclement weather and now for a beer....