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Steve, BMW Expert
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Experience:  BMW Expert
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My 2006 X5 3litre diesel won't start properly if I leave it

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My 2006 X5 3litre diesel won't start properly if I leave it more than a couple of days. When it does fire up it will be in trans. fail safe mode. The battery is new and turns the engine over but engine does not fire for a good few turns. the engine has done 60k so not high mileage. When the engine does fire in trans fail safe, I leave it running for 5 minutes, turn off then it will fire up almost instantly correctly. I took the car to a specialist autoelectrician and they said there was nothing wrong. There obviously is something wrong if it wont start. The car is also not as powerful as other X5's I've tried. Could lack of starting and lack of power be the same issue? Please help.
What faults are logged in the transmission computer?
Customer: replied 3 years ago.

I have not taken the car to a diagnostic centre so do not know how to check for faults. I do not think that it is the transmission although I am not an expert. The car is automatic and when it does start properly it changes gears quietly and I think correctly. The trans fail safe only comes on after the engine has been turning for a while with no actual start up. I was wondering whether it might be fuel (diesel) related. My concern is that it just doesn't start straight off and seems to be very underpowered.

I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.

if the transmission warning is going off, then faults are being stored by the transmission and the first step in diagnosis should be to have these faults read out using a BMW scan tool as they will provide great insight to what may be going on

I would suspect that the issue is the battery getting weak while the vehile sits (either the battery could be defective or there could be a drain on it when there should not be), then the low voltage causes the transmission issue and poor running. Once the battery has been able to charge from the alternator, power levels return to normal and the car and transmission run better.

I would advise you to have the vehcile tested for a parasitic drain and also to leave the vehicle with a BMW main dealer for several days so that they can fully replicate the issue and validate my suspicions. There is no way to verify the cause without such testing, and trying to guess at it will be a) unfruitful and b) expensive.

Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle

Customer: replied 3 years ago.

I did have the car tested for a drain as that was what I initially thought which was why I put a new battery on the car. The car was tested at the garage I bought it from who found no fault which was why I took it to the auto electrician who had it a week and found no drain. I am at my witts end with this car. It doesn't start in trans fail safe mode every time, probably 3 in 10 starts, but it never starts on the first click / turn of the key. Usually between 8 and 10 seconds of turning. When it starts in trans fail safe mode I leave it running for a few minutes then restart which it does fine (after 3 to 4 seconds of turning). I do use the car 3 or 4 times a week so it is never normally left for long. I don't trust it though so as a family car it is a bit of a waste of money. Well that's how I feel at the moment unless I can get to the bottom of it. I have been on various forums and been told that it might be a heater coming to life when the car is shut down so I have taken to not locking it, and sitting in it for a couple of hours to see if anything 'wakes up'. Someone else on the forum said it was the turbo. I really do need to solve this or my husband will want it sold.

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you.

Do not believe what you read in forums, they are fully of misinformation.

if anything was waking up, this would register as a drain - this is why I recommended extensive drain testing.

if you want this to be fully resolved, you will need to have furhter drain testing carried out, and as I suggested, leave the vehicle with BMW so they can let is sit for several days, then replicate the issue and carry out live testing while the issue is presenting itself. Everything you have described points to a voltage issue of some kind and this type of testing will be required to resolve it.

if you are not willing to invest in this kind of testing when the issue is present, then you may want to sell the vehicle becuase it is unlikely the problem will be resolvable otherwise.

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you.

Customer: replied 3 years ago.

But would a drain make the car underpowered when driven? Are you sure it is not a fuel issue? If you think that it is most definitely a drain I will take it to BMW for a week and see what they say.

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you.

I have not driven your vehicle so I cannot say what the power situation is like.

a difficult start can certainly be caused by lack of fuel, but this would not normally cause a transmission failsafe warning.

in any event, this is the path forward:

leave the car at BMW for long enough such that the issue will present itself when started. Make proper arrangements for theh vehicle to be left untouched for long enough, and also arrange that diagnostics will be immediately carried out when starterd. This will verify whether it is a voltage issue, a fuel issue, or something else.

Please do not forget to CLICK ON a positive rating as this is the only way I receive credit for my answer, thank you.

Steve and other BMW Specialists are ready to help you
Customer: replied 3 years ago.

Sorry to sound a bit stupid, but does the trans fail safe only come on if the engine reduces its load so that the battery just starts the engine and there is no fault actually in the transmission?

trans failsafe comes on when any transmission fault is sensed by the car


if you drive in failsafe, the transmission starts in high gear. this will make the car feel underpowerd.


so, if the car is only underpowered when in failsafe, there is no power issue, it is just the car starting off in high gear, which is more difficult for it to do

Customer: replied 3 years ago.

That is not what I asked, sorry if I am not being clear. I do not drive the car in fail safe mode. I restart the car and it starts fine once it has run for a couple of minutes. The question was; when I am turning the ignition for more than about 10 seconds, the battery is obviously working hard to power all the electronics on the car. If it doesn't start after that time the trans fail safe comes on and the car starts. Is this a safety feature so that the load is reduced so that the battery is able to start a reduced elecrtrically engine? Hope that makes sense.

Customer: replied 3 years ago.
Do I have to rate each answer as I thought I had already rated your service. I didn't rate your last comment as all you said was 'no' which wasn't very helpful.
you do not need to rate again.

I answered "no" because you asked a yes or no question which required no further elaboration.