Technical Battery warning light and no power steering

[Arvid]

In a way it's good news as I rather swap alternator than BCM. But it's still very puzzling.... Why wouldn't an non-OEM alternator work ? Every part shop being it online or indepentent garage offers Hella or Bosch for our cars. One should think there are numerous stories about the same problem.

Sadly I have no correct Denso to test,only one from an Alfa 159 1.9 150HP. Not same part nr. so not keen on plugging it in.

 

[aschiuta]

In a way it's good news as I rather swap alternator than BCM. But it's still very puzzling.... Why wouldn't an non-OEM alternator work ? Every part shop being it online or indepentent garage offers Hella or Bosch for our cars. One should think there are numerous stories about the same problem.

Sadly I have no correct Denso to test,only one from an Alfa 159 1.9 150HP. Not same part nr. so not keen on plugging it in.

The alternator dont send anything when you key on only. Whitout rotation the alternator can not send any voltage.
The BCM send the command to alternator ( in fact to alternator regulator ) in this situation.


Use the alternator you have from Alfa for test only. For that put the alternator cage to the car chassis, B+ to 12 volt car battery and D+ to BCM pin 25. You dont need to mount the alternator on the car. It is only test. So key on without start engine and measure the voltage from D+ to car chassis or minus terminal of car battery.

 

[Arvid]

As a test it would be interesting but I don't have easy access to a lift so next time the car is lifted I'll probably swap the alternator.

But,why exactly won't the Hella work ? Aren't most alternators built on same principal ?

 

[aschiuta]

As a test it would be interesting but I don't have easy access to a lift so next time the car is lifted I'll probably swap the alternator.

But,why exactly won't the Hella work ? Aren't most alternators built on same principal ?

You dont need to lift the car. Split the D04 connector and run a wire from D04 BCM side to Alfa D+ terminal.
The Alfa alternator will sit next to the car.

Yes, but the regulator differ. I suppose the BCM send 9 - 12 volts to alternator regulator aka D+ when key on and this regulator suck some curent from BCM in such way that the tension at D+ decreases at 1.3 level or under 5.5 volts as eLearn say. When start the engine the voltage at D+ will be same as alternator B+ terminal. The BCM feels the transition from 5 volts to 13.5 volts ( in fact it sense the modification of electrical current in the wire from D+ to BCM ) and declare everythink is ok. In your case you dont have this transition because at key on you have 9 volts on D+. So BCM thinks something is wrong and even it receives the 13.5 volts it declare the alternator dont work. This is me supposition.

 

[Arvid]

I can understand that explanation and it seems logic. I’m crossing my fingers and hoping this is the solution. Maybe I should give the Alfa alternator a test and see what happens…

 

[koalar]

The alternator dont send anything when you key on only. Whitout rotation the alternator can not send any voltage.
The BCM send the command to alternator ( in fact to alternator regulator ) in this situation.


Use the alternator you have from Alfa for test only. For that put the alternator cage to the car chassis, B+ to 12 volt car battery and D+ to BCM pin 25. You dont need to mount the alternator on the car. It is only test. So key on without start engine and measure the voltage from D+ to car chassis or minus terminal of car battery.

Fiat wording is the the alternator send the ground signal to the body computer

But correct the body computer is just having a pin pulled towards ground

Which is never going to happen as the alternator has over 100x more resistance on the D+ to ground than it’s supposed to have

 

[aschiuta]

I can understand that explanation and it seems logic. I’m crossing my fingers and hoping this is the solution. Maybe I should give the Alfa alternator a test and see what happens…

The test will show if the voltage at D+ will be other than 9.5 volts. Of course for this test you must to power the alfa alternator from car battery. If voltage on D+ remain at 9.5 volts than the BCM pin 25 may be defect.

 

[aschiuta]

Fiat wording is the the alternator send the ground signal to the body computer

But correct the body computer is just having a pin pulled towards ground

Which is never going to happen as the alternator has over 100x more resistance on the D+ to ground than it’s supposed to have

Alternator in fact the regulator cant send any signal because it dont have power. At key on the BCM send current to regulator to enable it but yet dont power on alternator. Only when alternator rotates the regulator will receive power send it to the rotor to have strong magnetic field and the voltage will appear at B+ and D+ terminals.

 

[koalar]

Alternator in fact the regulator cant send any signal because it dont have power. At key on the BCM send current to regulator to enable it but yet dont power on alternator. Only when alternator rotates the regulator will receive power send it to the rotor to have strong magnetic field and the voltage will appear at B+ and D+ terminals.

The original poster has 410K instead of 1.5K

There no way it can work


As per

If there is any other faults we can not say.

This car has multi high power faults I don’t thing I’d risk a working cars alternator in it.


You can check this alternator in another vehicle to confirm it’s not working. If under warranty just change it.

 

[aschiuta]

The original poster has 410K instead of 1.5K

There no way it can work


As per

View attachment 419132
If there is any other faults we can not say.

This car has multi high power faults I don’t thing I’d risk a working cars alternator in it.


You can check this alternator in another vehicle to confirm it’s not working. If under warranty just change it.

Yes I read that but it was written by an italian guy in english.
When the car is parked and you have the key in your pocket nothing feed the alternator.
Also at key on only BCM send signal to alternator D+ terminal nothing else change to alternator.
Figure show the situation at key on engine off:

BCM put 9-12 volts tension at pin 25 and send current through wire on D+ terminal.
We dont know if that current feed the regulator only the rotor only or both to create magnetic field on alternator rotor coil. May be this tension enable the regulator to close an inside circuit that feed the rotor coil with current from B+ alternator terminal but this is just a speculation. We dont know how internal this works.
What we know is voltage at D+ terminal is 1-1.3 volts as we measured it and must be lower than 5.5 volts as eLearn say. If you say you know the resistance between D+ and earth is 1.5 kohm then the current that flow from D+, through rotor, to earth is maximum 0.86 mA ( 1.3 volts divided at 1.5K ) and personal I think it is too low to produce enough magnetic field in rotor coil. Also I think the 1-1.3 volts it's too low for the alternator regulator to work.
When the car engine rotate the alternator the regulator will be feed with tension ( 13.5 - 14.4 volts ) by the three diodes connected to the D+ terminal and the regulator will work in parameters.
In case of HELLA alternator we dont have that initial current through D+ terminal and even the alternator start and have also 13.5-14.4 volts at D+ terminal the BCM did not feel any variation in the current through the wire and let the dashbord warning light on.

 

[Arvid]

I will check the pin 25 and connector itself further before ordering a new alternator. Just need to make sure this connection isn't causing problems. What happens inside BCM and pin 25 connection to printboard is not easy to judge. I had the BCM open and inspected under magnifier and it looked like new. If there is something wrong there it must be a component failure or a break in a circuit not visible to my eyes.

I delved into some German forums and there are plenty of stories on non-OEM alternators and battery warning lights spread between Fiat,Alfa and Opel which all use the same engine and alternator. Just looking for confirmation I guess so I need to wear dark sunglasses when reading those forums...

 

[Mike1alike]

If the problem is inside the BCM, you cannot see it under magnifier or by how it looks. Because if it is there, is probably a transistor, the inside of transistor, so you cannot see it if you don't cut open the transistor. And if you do cut it open... it's kind of like Schrodinger's cat (so that's the link that got you to german forums )
The transistors are easy to replace, though.
But I don't think the BCM is the problem, cause when a transistor breaks down, it doesn't go totally out of business, instead it works intermittently. So, it's not the case with your problem, as at yours it does not have moments when the problem goes away, to come back later.
What did the german folks said? Did they get to the bottom of it? Or just raised an eyebrow, seeing you peaking into their forums, wearing dark sunglasses?!

 

[Arvid]

Most of the stories was not conclusive as they often are on forums. I only found one Fiat-example that could match my faults and it needed an OEM Denso alternator to be fixed. In this case the Fiat mechanic told customer the Hella was not compatible with Fiat electronics. There were a few examples of Alfa Romeo 159 with constant battery warning light after installing other alternator - fixed with OEM alternator. On a Opel forum you have this statement : "However, there is no getting around the Denso generator as a spare part, because no alternator from another manufacturer has been integrated into the vehicle electrics/electronics"

I found it not very informative but it does indeed make a point that alternators are a sensitive subject on the 1.9 FPT engine or that era of models. And it does make a point to install Denso if the original should need replacing.

 

[koalar]

Yes I read that but it was written by an italian guy in english.
When the car is parked and you have the key in your pocket nothing feed the alternator.
Also at key on only BCM send signal to alternator D+ terminal nothing else change to alternator.
Figure show the situation at key on engine off:

View attachment 419164
BCM put 9-12 volts tension at pin 25 and send current through wire on D+ terminal.

Wrong at key on it’s not sending anything to the winding around 1V

We dont know if that current feed the regulator only the rotor only or both to create magnetic field on alternator rotor coil. May be this tension enable the regulator to close an inside circuit that feed the rotor coil with current from B+ alternator terminal but this is just a speculation. We dont know how internal this works.
What we know is voltage at D+ terminal is 1-1.3 volts as we measured it and must be lower than 5.5 volts as eLearn say. If you say you know the resistance between D+ and earth is 1.5 kohm then the current that flow from D+, through rotor, to earth is maximum 8.6 mA ( 1.3 volts divided at 1.5K ) and personal I think it is too low to produce enough magnetic field in rotor coil. Also I think the 1-1.3 volts it's too low for the alternator regulator to work.
When the car engine rotate the alternator the regulator will be feed with tension ( 13.5 - 14.4 volts ) by the three diodes connected to the D+ terminal and the regulator will work in parameters.
In case of HELLA alternator we dont have that initial current through D+ terminal and even the alternator start and have also 13.5-14.4 volts at D+ terminal the BCM did not feel any variation in the current through the wire and let the dashbord warning light on.

I will try one last time

Key on but not crank

The floating voltage from body computers buffer is pulled to close to 0V via the alternator internal resistance effectively a “pull down resistor” the body computer monitors the D+ For low voltage

Key on and cranking, the body computer then sends battery voltage to the D+ to energise the windings

Engine on rpm over 700 the body computer again starts to monitors from D+

Step one can’t happen due to to higher resistance 410k vs 1.5K

You could probably fool the system with a incandescent test between ground and D+ Cable and get someone else to crank. Not sure if this a good idea

If any sensing step is detected wrong the body computer will switch the EPS and sends a signal to the dash to put the warning light on.

The more we mess with the setup the more chance we have of causing more problems

 

[aschiuta]

I dont think the pin 25 of BCM deliver current for rotor. It is thin wire.
Arvid can try to know how much current pin 25 deliver using these scheme also if the voltage at pin 25
is under 5.5 volts with that scheme he can fool the BCM and use Hella alternator.

 

[aschiuta]

Today was a sunny day so I open the D04 connector , key in my pocket, and:
1. on D+ side, resistence between chassis and D+ ,measured with multimeter probes in both directions = 270 ohm.
2. on BCM side, resistence between chassis and pin 25, also both directions = 1Kohm
Key on:
- 9.5 volts on pin 25, 0 volts on D+.
Then I inserted the big multimeter as ammeter in circuit and you and see the result in the image.
I could not start the engine with D04 open.

 

[Arvid]

You have the same 9.5v I measured on mine. I did not measure current when I worked on it and I see yours draw 1.33A.
I feel I have done what I can do so far and I'm very grateful for the advice and help from all forum members who contributed. It would have been a long fight without this help.

I chose to order a new Denso and have my fingers crossed for the results after install.

 

[aschiuta]

You missunderstood, the current is 31.4 mA and voltage on alternator = 1.33 volts. This 31.4 mA current is limited by BCM. This is the maximum current the pin 25 output can deliver. When engine start on pin 25 you will have the voltage of B+ terminal = 13.5-14.4 volts and pin 25 do not deliver any current.
If your Hella alternator with engine started have 14 volts at D+ terminal then is very simple to fool the circuit and use Hella alternator. For this you must disconnect the wire from D+ and measure on D+ the voltage with alternator running or cut the wire from BCM pin 25 and D+ terminal and measure the voltage on side of the wire from D+ terminal of course with alternator running.

 

[Arvid]

Here is an update. New Denso received yesterday. Hooked it up to a battery with positive terminal to B+ and negative to alternator chassis. Measured resistance between D+ and chassis and it was 1.15Kohm. A huge difference from the Hella 410Kohm. So far so good and got a feeling that this might work. Today we jacked up the car and crawled under and the new Denso was installed. What a pain of a job....

Long story short : It worked I now have a working power steering and no battery warning light. It's a huge relief to say the least. A huge Thank You to all who participated in guiding me through this

 

[koalar]

Hi all,

I have been searching through the forum and read what I could find on the subject - but I just can't find any good leads on how to fix the issue. I recently bought a cheap 2009 Bravo 1.9 Mjet to have as an all round daily driver. It came with battery warning light and no power steering. Before purchase it got a new alternator and I have put in a new 77Ah battery. Last owner was told that the problem might be in the BCM.

I have done several checks but has not been able to solve the issue and I have not been able to determine if the problem is with the BCM or the power steering unit. These are the symptoms :
- No power steering
- Battery charge light constant
- Main earth chassis/engine replaced and cleaned
- Alternator puts out 14,4v on idle
- Error code B1020 Alternator D+ signal
- No red power steering warning light

I have measured voltage on D+ from alternator and it's 13,8v. Is this enough for the BCM to register alternator charging ? Should it be equal as the charge voltage 14.4 ?? The D+ wire is measured and complete from alternator and in to BCM connector. I have also measured 14,4v on power steering connector with engine running and 12.6v with engine off.

Last owner disconnected all connectors on BCM and found that the PS was then working but not much else. Is this to be understood as it's a BCM fault ? I am at a loss here and can't seem to get any further. We have no trained Fiat garages in my area so a garage fix will be a two hour drive so that will be the last option eventually.

Many thanks,
Arvid

Cool

Great result

Turning out to be FOF (fail on fit) alternator

Is much better than the mega bucks required to replace and program a BCM

Plus another one back on the road

Well done