Car wonโ€™t start - battery fine.

Car wonโ€™t start - battery fine.

Author
Discussion

ian332isport

83 posts

198 months

Tuesday 15th June
quotequote all
MitchT said:
Having disconnected the CTEK at lunchtime I’ve just tested the battery with a multimeter - rightly or wrongly, given the conflicting advice in this thread. Anyway, it read 12.75V which seems OK. I’ll try again tomorrow evening when it’s had more of a chance to drain but, for now, I’m increasingly of the belief that it’s not a battery issue.
From what you say about the central locking and windows working as normal, and the 12.75V at the battery, I agree with you that it's probably not the battery.

As others have mentioned, battery voltage alone does not prove the battery is good. You could see a large voltage drop when the battery is under load, but I would expect the windows to struggle if this was the case.

MitchT

Original Poster:

13,726 posts

176 months

Tuesday 15th June
quotequote all
ian332isport said:
Next step is to check for 12v on X20 pin 18 while cranking.
When you say “while cranking”, do you mean while the key is turned fully clockwise? I ask as no actual cranking happens. When the key is fully turned clockwise and the starter motor should operate, nothing happens at all.

paintman

6,536 posts

157 months

Wednesday 16th June
quotequote all
With the meter connected across the battery try & start the car - you may need to get someone to do it for you if the battery is in a place where you can't turn the key & see the meter at the same time.

See what the voltage reads when the key is in the cranking position.

ian332isport

83 posts

198 months

Wednesday 16th June
quotequote all
MitchT said:
When you say “while cranking”, do you mean while the key is turned fully clockwise? I ask as no actual cranking happens. When the key is fully turned clockwise and the starter motor should operate, nothing happens at all.
Yes, while actually trying to start the car.

If you don’t have 12(ish) volts on X20 pin 18, the problem is somewhere between the ignition switch and pin 18.

If you do have 12v, then the problem is between pin 18 and the starter (or the starter itself).

MitchT

Original Poster:

13,726 posts

176 months

Wednesday 16th June
quotequote all
Thanks both - I'll try to take a look at lunch time. Failing that, after work.

S54B32

7,452 posts

135 months

Wednesday 16th June
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Battery cable to the starter could be gone. Not common on these cars, but worth checking

MitchT

Original Poster:

13,726 posts

176 months

Wednesday 16th June
quotequote all
Just had another quick go with the mutimeter...

Today's readings:

12.66V - no key.
12.65V - key in position 1.
12.48V - key in position 2.
12.47V - key in cranking position.

I don't know if any of that reveals anything useful to anyone more knowledgeable than myself.

I'll investigate the "X20 pin 18" and battery cable possibilities after work.

Edited to add...

At risk of sounding stupid, can someone explain what is meant by "X20 pin 18"?

Edited by MitchT on Wednesday 16th June 14:25

phumy

5,114 posts

204 months

Wednesday 16th June
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Do you have another car available or a friend who could assist with some jump leads and jump start the car?

MB140

2,889 posts

70 months

Wednesday 16th June
quotequote all
MitchT said:
Just had another quick go with the mutimeter...

Today's readings:

12.66V - no key.
12.65V - key in position 1.
12.48V - key in position 2.
12.47V - key in cranking position.

I don't know if any of that reveals anything useful to anyone more knowledgeable than myself.

I'll investigate the "X20 pin 18" and battery cable possibilities after work.

Edited to add...

At risk of sounding stupid, can someone explain what is meant by "X20 pin 18"?

Edited by MitchT on Wednesday 16th June 14:25
The fact your only dropping 0.1 volt when the starter motor should be attempting to crank over suggests to me it’s not even attempting to start. I would expect it to be multiple volts not 0.1v.

Immobiliser, key switch problem, starter solenoid relay. Assuming you have checked all the relevant fuses.

I’f the starter motor was just stuck (hence people telling you to hit it/rock the car) then you would be seeing a much bigger voltage drop.

S54B32

7,452 posts

135 months

Wednesday 16th June
quotequote all
If it was the battery, the clocks/lights/everything in the car would go dead as soon as you try to engage the starter motor..

ian332isport

83 posts

198 months

Wednesday 16th June
quotequote all
MitchT said:
At risk of sounding stupid, can someone explain what is meant by "X20 pin 18"?
I mentioned it in one of my previous posts. Most BMW connectors have an X number for identification purposes on the wiring diagrams. X20 is the designation for the big 25 pin connector next to the fuse box. This connector is the main connection between the body wiring harness and the engine wiring harness.

There's actually a couple of similar connectors next to each other, but the X20 is the one nearest the strut tower. The one at the back is the X69 connector.

If you pull the rubber boot back, you can access the wires inside. You may need to unclip it from its mounting to get the boot off. You'll find a small screwdriver helps to hook the boot back.

Once inside, you want to find the wire on pin 18. They are numbered on the plastic housing, but it's not easy to see. Just look for a reasonably fat wire that's yellow with a thin black stripe. This wire absolutely must go to 12v when you try to start the car. This is the signal that tells the starter solenoid to activate. It's basically the other end of the wire that comes from the ignition switch, although it passes through the EWS relay on the way.

Penelope Stopit

8,721 posts

76 months

Wednesday 16th June
quotequote all
MB140 said:
MitchT said:
Just had another quick go with the mutimeter...

Today's readings:

12.66V - no key.
12.65V - key in position 1.
12.48V - key in position 2.
12.47V - key in cranking position.

I don't know if any of that reveals anything useful to anyone more knowledgeable than myself.

I'll investigate the "X20 pin 18" and battery cable possibilities after work.

Edited to add...

At risk of sounding stupid, can someone explain what is meant by "X20 pin 18"?

Edited by MitchT on Wednesday 16th June 14:25
The fact your only dropping 0.1 volt when the starter motor should be attempting to crank over suggests to me it’s not even attempting to start. I would expect it to be multiple volts not 0.1v.

Immobiliser, key switch problem, starter solenoid relay. Assuming you have checked all the relevant fuses.

I’f the starter motor was just stuck (hence people telling you to hit it/rock the car) then you would be seeing a much bigger voltage drop.
This

NMNeil

2,129 posts

17 months

Wednesday 16th June
quotequote all
Grab a multimeter and start at page 118
https://bimmertips.com/wp-content/uploads/BMW_Wiri...

ian332isport

83 posts

198 months

Wednesday 16th June
quotequote all
NMNeil said:
Grab a multimeter and start at page 118
https://bimmertips.com/wp-content/uploads/BMW_Wiri...
Careful with that. North American wiring diagrams are different to UK versions.

MitchT

Original Poster:

13,726 posts

176 months

Wednesday 16th June
quotequote all
First:
Checked the fuses. All look OK.

Second:
ian332isport said:
I mentioned it in one of my previous posts. Most BMW connectors have an X number for identification purposes on the wiring diagrams. X20 is the designation for the big 25 pin connector next to the fuse box. This connector is the main connection between the body wiring harness and the engine wiring harness.

There's actually a couple of similar connectors next to each other, but the X20 is the one nearest the strut tower. The one at the back is the X69 connector.

If you pull the rubber boot back, you can access the wires inside. You may need to unclip it from its mounting to get the boot off. You'll find a small screwdriver helps to hook the boot back.

Once inside, you want to find the wire on pin 18. They are numbered on the plastic housing, but it's not easy to see. Just look for a reasonably fat wire that's yellow with a thin black stripe. This wire absolutely must go to 12v when you try to start the car. This is the signal that tells the starter solenoid to activate. It's basically the other end of the wire that comes from the ignition switch, although it passes through the EWS relay on the way.
Mine seems to be at the opposite side from the fuse box. I'm guessing it's this...



Amazingly, I can read the tiny numbers next to the holes. The question still remains... if I manage to expose the pin 18 wire, how do I test it? If I'm using the multimeter, which probe goes on the wire and where does the other probe go?

ian332isport

83 posts

198 months

Wednesday 16th June
quotequote all
No, that’s the diagnostic socket.

ian332isport

83 posts

198 months

Wednesday 16th June
quotequote all
When you do find the X20 connector, you need to connect the meters black lead to any bit of exposed metal on the car. One of the bolts on the strut top is usually a good one. If the battery is under the bonnet, you could go direct to the negative terminal too.

Then poke the red lead down in the back of pin 18. It may have a rubber seal where the wire exits the connector which makes it a bit tricky to get the probe in. At a push, ask the wife for a pin or needle to poke down the hole and then touch the probe on that.

MitchT

Original Poster:

13,726 posts

176 months

Wednesday 16th June
quotequote all
I'm stumped then. Is anything that's visible in this photo the X20?


ian332isport

83 posts

198 months

Wednesday 16th June
quotequote all
Not in that picture. No.

Can you do a general picture of the engine bay?

shakindog

436 posts

117 months

Thursday 17th June
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Always Start with the basics
Battery
Starter
Fuses
Wiring
Volt drop earths
It’s very easy to get you leg in going down the wrong path and waste hours trying to work it out when it could be and usually is something simple.
The exciter wire to the solenoid could have come adrift,earth wire loose,corroded a whole multitude of things.
No offensive to other contributors but the immobiliser module blah blah blah is way down the list of things to check.
As has been said plenty of folk will give you plenty of different answers.
Worst case if you have breakdown ring them as they will do all the above and at least point you in the right direction from actually being in front of the car and can see hear what’s happening not vague descriptions coloured by their own experience.
All the above is imho of course.