Intermittent Starting Issue

[Mattwz]

Hi all. I’ve had my Z4 for a year and over the last 6 months it’s developed an annoying starting issue. I’ve read many posts on here and have tried a few things which haven’t helped.

Battery was changed 12m ago
Ignition switch on rear of ignition barrel replaced.
Starter motor replaced with a new Bosch unit

The issue is now happening regularly. When I unlock the car, get in, turn the key, I get dash lights but nothing else, no attempt for the car to start. If I then press the unlock button on my key fob it then fires into life straight away (however not always, might need 1 or 5 attempts but it never struggles to crank - it’s all or nothing).

I’m a bit stuck now for ideas on what the issue might be, perhaps the key battery or immobiliser? I’ve tried sticking it on an electric toothbrush charger but it’s not helped.

 

[chanlon1]

It's tough to properly identify when it's not happening all the time.
I had intermittant starting issues, and then one day it wouldn't start at all. Battery wasn't at fault, nor did a new ignition switch solve it. New starter motor was put in and car still didnt start. Turns out it was a corroded earth ground strap.
Thread details it all: https://z4-forum.com/forum/viewtopic.php?t=146806

 

[colb]

Earth strap is a good call, check yours if that isn't the problem then with the absence of any fault codes start looking at camshaft sensor and crank sensor and their wiring, look for corroded plugs and terminals on these, clean them first before throwing replacement parts at it.
Regarding the earth try putting a temporary earth lead from the negative battery post in the engine bay to a solid metal part of the engine and see if that solves it.
I think when you press the unlock button that has nothing to do with a failed start as that part of the keys system has nothing to do with starting the car, its just communicating with the GM5 module that controls the locks and windows and wipers. Its the actual non powered transponder chip in the key that is read by the aerial around the ignition barrel when the key is put into the ignition and sends its code to the EWS security module behind the drivers side footwell panel that releases the starter and allows the car to crank. Worth checking the ignition lock aerial and taking a look at the EWS module connections, ensure they are clean and dry.

 

[enuff_zed]

Do you have two keys? Is it the same with both?
Don't rule out a replacement component being faulty. Was the ignition switch new or secondhand?

 

[Mattwz]

Thanks for the replies, a few things there for me to consider and check out.

The replacement ignition switch was new (non genuine BMW).

 

[chanlon1]

any joy on getting it resolved?

 

[Mattwz]

No not yet but it’s not happens for the last week or so!

 

[chanlon1]

No not yet but it’s not happens for the last week or so!

quite frustrating when that happens