I have a bizzare issue with an intermittent but predicatable fault - this is proving quite a challenge even for a long term Land Rover driver!
The car is well maintained low mileage and everything works perfectly except for quite often cutting out with about a dozen communication faults stored in the different ECU's. It has ALWAYS done this five minutes into a journey - not every journey but always at five minutes, irrelevant if the engine is hot or cold. On the first couple of occasions it will start and run in limp mode after a few seconds of cranking - on the second or third restart it would be fine - no errors at all on the dash.
Lately it has taken longer to start once the fault occurs and would flatten the battery trying - have left it for a couple of hours and it starts fine again.
I have been through all the usual earth points and everything looks fine and solid - the battery has been replaced.
The faults all seem to do with the BCM, gearbox, ABS and plenty of other modules which seems like they loose communication somehow - I assume it's something they have in common as there are no permanent faults stored other than a handbrake actuator.
Does anybody have any thoughts where to start this this one? Or know of a Land Rover magician in Wiltshire area??

PS - just tried to start the car after 2 hours on the recovery truck - started perfectly no faults at all on the dash. Ran the diagnostics and cleared lots of injector data faults and crankshaft position sensor fault all 'intermittent' - checked again and all faults gone with engine idling. Five minutes later at tickover the engine simply shut off - nothing on the dash - won't restart - ran diagnostics again and voilla - crankshaft position sensor error - this time 'permanent'
Would that really cause all these issues? A simple crank sensor? Surely this failure won't prevent the engine running in limp mode?

I’ve given up trying to apply logic to intermittent faults particularly electrical ones. Trying to second guess what the fault messages mean will make your head explode. If it were mine I’d start with a crank sensor.

Thanks for the reply - yes I've been pulling my hair out with this one - luckily it just died while idling after I'd cleared all the faults and there were only a handful of new ones that appeared - I guess because it wasn't in gear and moving, faults like gearbox and abs didn't throw up so I can narrow it down a bit. I'll have a crawl around and check the crankshaft sensor plug next, the sensor itself looks like it's nearly impossible to get to, so might have to take it to someone with hands like Mr. Tickle...

Quarryman wrote:

Would that really cause all these issues? A simple crank sensor? Surely this failure won't prevent the engine running in limp mode?

Monitor RPM while cranking with a diagnostic tool. Zero RPM or a momentary dropping to zero implies a failing crankshaft position sensor.

Yes - I did try to find the values of the engine speed in the live data but couldn't see it initially however having the permanent fault now logged when the engine won't start points to the culprit. I'm just surprised that such a single point of failure can throw gearbox faults on the dash yet nowhere did the car complain of any engine fault. Only when it was stationary in park when the fault occurred could it be identified as the probable cause. I did assume that all sensors such as these have a backup nowadays - ie use the cam sensor to at least best guess the injection timing and get the engine running albeit in limp mode - I noticed some Discoveries of the same age were recalled due to the safety implications of this sensor failing, so I assume it is indeed a critical weak link.

I had a similar issue on a Ford Explorer and it turned out to be the connector to the crankshaft sensor was dirty. If you can reach the sensor try pulling the connector off and on a few times. Worth a go.

Thanks for that - yes I will have a look at the plug connections at the weekend to see if they are loose or corroded, it definitely seems worse when the engine and weather is warm so could be just that.

Monitor rpm as a live value rather than go looking for the crankshaft position sensor to monitor which I doubt you'll find.
Crankshaft position sensors failing as soon as they get hot is common. On engines where the sensor is mounted behind the crankshaft pulley the trick is to spray a can of drink on it which cools it and gets it working for a little while. Unfortunately the sensor in these engines is at the back of the crankshaft, accessed by removing the starter motor but otherwise accessible.

Last edited by GraemeS on 13th Aug 2024 9:54am. Edited 1 time in total

The car is running fine now and the live value is fine when cold. The crank position diagnostics gives the P0036 failed error when the car is hot and won't start so what would be the benefit of checking the value when cranking? Surely the 'permanent' error code when it fails to start is the reason for not starting and it can only be the sensor or sensor wiring fault or am I missing something?

Often there isn't a fault code so seeing a flat 0 line or dipping to 0 while cranking is evidence.

Oh thanks I see - well this definitely had the fault code stored as permanent after a failed start attempt so I assume it's not lying to me.
I just removed the sump guard to have a quick look and everything must be well hidden behind the starter motor - can't even see a cable or plug without removing things. I have booked it into the local garage to fit a new sensor but won't be for a couple of weeks.