I acquired a Z4 2.5 2004 from ebay really cheap.
After owning it for about a week I was driving along and I realized I could not tell the difference between main and dip beams. Then most of the Dashboard lights came on (Engine / Traction Control / EML / Tyre Pressure etc….). The head lights went even dimmer, the electric power steering failed, everything else failed and the car went into limp mode (Would not rev at all and was running really ‘lumpy’) . Having rolled it off the road and gathered my thoughts I suspected an alternator / charging / battery problem even though No Battery warning light illuminated (However it did illuminate when parked with just Ignition on). The AA man came along and confirmed with a Multimeter that the alternator was not putting out enough charge. He wacked it with a hammer and it came back up to 14v.
So I got myself a Multimeter and found out the following before using it.
i) A Multimeter has such high internal resistance that hardly any current will flow through it - Even if you connect it straight across the battery terminals it won’t melt!
ii) Also it does not matter which way round you connect the multimeter- You’ll just get neg figures instead.
iii) My Multimeter was about £8.50p and is perfectly adequate.
Once the car was back at my place -I did the following tests with it.
- Multimeter across battery terminals. 12.5V with car not running indicating the battery is well charged. Then 13.8V with the car running indicates the Alternator is charging it well. The running voltage should be about 1.0v-1.5v above the standing battery voltage).
- Multimeter across battery terminals with starter motor cranking - Take note of the lowest value. Should not go under 10.5V when cranking - That indicates a good battery.
- Multimeter from Alternator Body to Negative Battery terminal (Or Car body) with car running. I got 0v which is a good reading. This low reading indicates there is no resistance / bad connections on the Negative Side. The alternator earths through it’s body so a high multimeter reading would indicate the electricity is finding it easier to go through the mutimeter to the Negative battery terminal rather than through the earth / car body back to the Negative battery terminal. (Should be no more than 0.2V)
- Multimeter from B post on Alternator (Where the fat red cable joins the Alternator) to Positive Battery Terminal. I got 0.0V with car running- This indicates there’s no bad connections / resistance between the Alternator output and the positive battery terminal. (Should be no more than 0.2V)
- Multimeter from B post on Alternator (Where the fat red cable joins) to earth (12.5v with car off) (13.8v with car running- This indicates the alternator is charging).
- Multimeter on Small Alternator wire to earth gave 8.5V - 9.0V. Don’t know what that means.
All looks good but I put a replacement (used) Alternator on anyway as i thought it might be the internal brushes. Then cleaned up all the terminals /connections I could find on the car.
Went down the road and it ran out of power - No Battery warning light illuminated.
Got it back and all tested again and looked good.
Put on a new Regulator onto the back of the alternator.
Went down the road and it ran out of power - No Battery warning light illuminated.
Took the alternator to a local Specialist who put it on a bench test and said “Regulator problem.” Then he said “Aha” and put a nut on the B2 terminal (That’s the OTHER heavy terminal on the back that appears to do nothing). Yes a nut IS required here. This is where the regulator makes contact with the body of the Alternator so it MUST have a nut on there and it must be tight and it MUST make a good connection. It’s very easy to think that terminal is doing nothing and ignore it while lavishing attention on the B1 terminal. (When your alternator is still on the car you most likely won’t even see the B2 terminal as there’s a plastic cap on the end of it). Without that connection being good you won’t get a circuit for the Field Coils. Ie No magnetism in the Alternator. I removed the Regulator and cleaned that contact (I mean the contact that hangs off the bottom of the regulator and is Shaped like the end of a Spanner) then I refitted and tightened everything up.
There’s also a small screw on the end of the diode pack that appears to make a contact through a copper loop – Cleaned it up and tightened that as well.
Went down the road and it ran out of power - No Battery warning light illuminated.
Got it back - Did all the tests again and all looked good.
Then I tried to start it and just got a click. Flat Battery? No still 12.0v there. So I looked at the Starter Motor terminal – HANGING OFF! Yes the cable to the starter motor was not even finger tight. Because the route of this cable is totally hidden under the manifold it’s very easy to assume the cable goes direct from the back of the Alternator to the Positive Mounting point on the bulkhead – No it stops off at the starter motor and then a 2nd cable (On the same post on the Starter motor) goes up to the Positive Post on the bulkhead. I took the heavy cables off the Starter Motor and cleaned them up then put them back on really tight. (Note – Disconnect your battery while doing this as you’re using a metal spanner on a positive wire with lots of earth points nearby).
So despite all my multimeter tests being good there was a seriously bad connection from Alternator / Starter / Battery which only showed up as an intermittent fault. The moral of this story is – While doing multimeter tests get your assistant to give all the leads wires a yank to make sure there’s no itermittent fault.
Now at 13.5v – 14.0v after a lot of headache.
Note – The regulator I was sent was for a slightly different BMW model, this means the ECU on my Z4 does not ‘understand’ it protocol / language. That’s not a problem, it just means that smart charging is disabled. The ECU can no longer command the alternator to drop it’s output to save drag / fuel. (The ECU does this by varying the Alternator field coils). So my Alternator has defaulted to maximum output at all times. The only other thing to note is you’ll get fault codes “Generator Serial Interface 281C & 281D” . You’ll only see that if you run a scanner on it – No engine lights or other indications at all.
Note- I now keep a voltmeter plugged into the cigarette lighter socket. It has USB plugs on it so I think its main purpose is to charge up mobile phones and display the voltage for that purpose.
Note - My local Alternator specialist advised that the small wire plugged into the back of the alternator should run at about +9 volts (He put +12v onto it when doing a bench test). He said it’s function is the battery light wire (I assume it must also be how the ECU commands the alternator?). I’m passing on this knowledge as I could not find any info on the internet what the voltage there should be.
Note- All of the above text refers to a BMW Z4 2.5 Litre of 2004 which has a Bosch Alternator. Other / Later models may differ.
My intention in writing this is to repay the forums which have helped me so much.
After owning it for about a week I was driving along and I realized I could not tell the difference between main and dip beams. Then most of the Dashboard lights came on (Engine / Traction Control / EML / Tyre Pressure etc….). The head lights went even dimmer, the electric power steering failed, everything else failed and the car went into limp mode (Would not rev at all and was running really ‘lumpy’) . Having rolled it off the road and gathered my thoughts I suspected an alternator / charging / battery problem even though No Battery warning light illuminated (However it did illuminate when parked with just Ignition on). The AA man came along and confirmed with a Multimeter that the alternator was not putting out enough charge. He wacked it with a hammer and it came back up to 14v.
So I got myself a Multimeter and found out the following before using it.
i) A Multimeter has such high internal resistance that hardly any current will flow through it - Even if you connect it straight across the battery terminals it won’t melt!
ii) Also it does not matter which way round you connect the multimeter- You’ll just get neg figures instead.
iii) My Multimeter was about £8.50p and is perfectly adequate.
Once the car was back at my place -I did the following tests with it.
- Multimeter across battery terminals. 12.5V with car not running indicating the battery is well charged. Then 13.8V with the car running indicates the Alternator is charging it well. The running voltage should be about 1.0v-1.5v above the standing battery voltage).
- Multimeter across battery terminals with starter motor cranking - Take note of the lowest value. Should not go under 10.5V when cranking - That indicates a good battery.
- Multimeter from Alternator Body to Negative Battery terminal (Or Car body) with car running. I got 0v which is a good reading. This low reading indicates there is no resistance / bad connections on the Negative Side. The alternator earths through it’s body so a high multimeter reading would indicate the electricity is finding it easier to go through the mutimeter to the Negative battery terminal rather than through the earth / car body back to the Negative battery terminal. (Should be no more than 0.2V)
- Multimeter from B post on Alternator (Where the fat red cable joins the Alternator) to Positive Battery Terminal. I got 0.0V with car running- This indicates there’s no bad connections / resistance between the Alternator output and the positive battery terminal. (Should be no more than 0.2V)
- Multimeter from B post on Alternator (Where the fat red cable joins) to earth (12.5v with car off) (13.8v with car running- This indicates the alternator is charging).
- Multimeter on Small Alternator wire to earth gave 8.5V - 9.0V. Don’t know what that means.
All looks good but I put a replacement (used) Alternator on anyway as i thought it might be the internal brushes. Then cleaned up all the terminals /connections I could find on the car.
Went down the road and it ran out of power - No Battery warning light illuminated.
Got it back and all tested again and looked good.
Put on a new Regulator onto the back of the alternator.
Went down the road and it ran out of power - No Battery warning light illuminated.
Took the alternator to a local Specialist who put it on a bench test and said “Regulator problem.” Then he said “Aha” and put a nut on the B2 terminal (That’s the OTHER heavy terminal on the back that appears to do nothing). Yes a nut IS required here. This is where the regulator makes contact with the body of the Alternator so it MUST have a nut on there and it must be tight and it MUST make a good connection. It’s very easy to think that terminal is doing nothing and ignore it while lavishing attention on the B1 terminal. (When your alternator is still on the car you most likely won’t even see the B2 terminal as there’s a plastic cap on the end of it). Without that connection being good you won’t get a circuit for the Field Coils. Ie No magnetism in the Alternator. I removed the Regulator and cleaned that contact (I mean the contact that hangs off the bottom of the regulator and is Shaped like the end of a Spanner) then I refitted and tightened everything up.
There’s also a small screw on the end of the diode pack that appears to make a contact through a copper loop – Cleaned it up and tightened that as well.
Went down the road and it ran out of power - No Battery warning light illuminated.
Got it back - Did all the tests again and all looked good.
Then I tried to start it and just got a click. Flat Battery? No still 12.0v there. So I looked at the Starter Motor terminal – HANGING OFF! Yes the cable to the starter motor was not even finger tight. Because the route of this cable is totally hidden under the manifold it’s very easy to assume the cable goes direct from the back of the Alternator to the Positive Mounting point on the bulkhead – No it stops off at the starter motor and then a 2nd cable (On the same post on the Starter motor) goes up to the Positive Post on the bulkhead. I took the heavy cables off the Starter Motor and cleaned them up then put them back on really tight. (Note – Disconnect your battery while doing this as you’re using a metal spanner on a positive wire with lots of earth points nearby).
So despite all my multimeter tests being good there was a seriously bad connection from Alternator / Starter / Battery which only showed up as an intermittent fault. The moral of this story is – While doing multimeter tests get your assistant to give all the leads wires a yank to make sure there’s no itermittent fault.
Now at 13.5v – 14.0v after a lot of headache.
Note – The regulator I was sent was for a slightly different BMW model, this means the ECU on my Z4 does not ‘understand’ it protocol / language. That’s not a problem, it just means that smart charging is disabled. The ECU can no longer command the alternator to drop it’s output to save drag / fuel. (The ECU does this by varying the Alternator field coils). So my Alternator has defaulted to maximum output at all times. The only other thing to note is you’ll get fault codes “Generator Serial Interface 281C & 281D” . You’ll only see that if you run a scanner on it – No engine lights or other indications at all.
Note- I now keep a voltmeter plugged into the cigarette lighter socket. It has USB plugs on it so I think its main purpose is to charge up mobile phones and display the voltage for that purpose.
Note - My local Alternator specialist advised that the small wire plugged into the back of the alternator should run at about +9 volts (He put +12v onto it when doing a bench test). He said it’s function is the battery light wire (I assume it must also be how the ECU commands the alternator?). I’m passing on this knowledge as I could not find any info on the internet what the voltage there should be.
Note- All of the above text refers to a BMW Z4 2.5 Litre of 2004 which has a Bosch Alternator. Other / Later models may differ.
My intention in writing this is to repay the forums which have helped me so much.
