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How to access starter to measure current draw? (A0C1 CAS Output, terminal 50 )

7K views 36 replies 5 participants last post by  SunglassesGuy 
#1 ·
I've got a no crank situation. Can hear starter solenoid click once when I push the start button. A section of the ISTA+ test plan says to measure current draw from starter. Is there a place to do this other than the starter? Can the starter be accessed very easily to do this?
 
Discussion starter · #4 · (Edited)
Thanks Guys. Gonna take me a few days to try all this, was simply trying to move the car so I could work on wife's car. Do you see anything in these ISTA read outs that point to a problem.

BTW - Where is this mysterious Terminal 50 located?

Starter Enable = Not active? Does this only go active when the start button is pushed?
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Terminal 50E 0.0V , Terminal 15 , Wake up (ACC) = 0.13V ?

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Discussion starter · #6 ·
Where is the circuit that activates the starter solenoid? I've gone thru ISTA verbatim and can't find it. Terminal 50 ends at the DME, and can't find it traveling over to the starter solenoid?
 
Discussion starter · #11 · (Edited)
Thanks again Guys, I'm working with a 2009 M6, but it looks like the last circuit diagram that ZiMMie posted matches (Numbers are a bit different, but basically same circuitry). My version of the TIS just didn't show the starter details, this is very helpful. Another thing that is a little different is the CAS/DME pins. Correct me if I'm wrong but it looks like for the M6, CAS Terminal 50 connects to Pin 2 of the DME at the 60001 connector?

I will measure voltages and resistances and try the hammer whack. Was also wondering if I put the car in gear, and just push on it a bit, maybe that would accomplish same thing as hammer whack. The starter was replaced a few years ago, just before I bought the car. I have no paper work to verify that tho.

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Is there a way to attempt to easily jump these two points (In Red) so I don't have to tear plenums off to access the starter? (Oh and do it with out burning some electronics out along the way?) I've been wondering when people open up their CAS and find a burnt Terminal 50, its because they tried to hotwire the car by connecting B+ directly to the starter solenoid, which would send B+ back to Terminal 50 area.

One other question: What is going on inside the Starter at #4 ? This looks like a switch, what opens and closes it? And what do the little rectangles with a slash thru them represent? (items #2, 3 inside the starter)

EDIT: Think I found the answer to the Starter components question: 6 Complete Starter Solenoid Parts, Functions & Working: ECE

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Discussion starter · #13 ·
Thanks guys. Gotta rebuild my wifes brakes - new calipers, replace rotor, pads and bleed the system. Hopefully I'll get her brakes done by Tuesday (hopefully Monday) and then do some testing on the M6 next week.

I did have some friends help me move the M6 over to the other stall so I can get wifes car onto the lift. So tried to nudge the M6 while in gear. Didn't help.

Platii BTW - Why whack the starter? Are you wondering if something inside the starter could be stuck?
 
Discussion starter · #15 ·
new info: Terminal 50E reads 11.8 V when pressing start and terminal 50L reads 53 Amps
 
Discussion starter · #17 ·
I chased this code and no crank condition on my 6MT for a while, it was the starter. Replaced it from the top, not a terrible job. Fine ever since, it’s been over a year.
I saw a DIY on this, apparently there are 2 methods, one actually remove the entire starter, and one, leave housing in place and replace guts. Which did you do? Also, starter was supposedly replaced about 2 years ago, just before I bought car. I have no documentation to prove tho.
 
Discussion starter · #19 ·
I left the housing and replaced the guts. 2 year old starter should be fine though… interesting. Good luck with the diagnosis
any major difficulties that you recall as you replaced the guts?
 
Discussion starter · #21 · (Edited)
Thanks N_Rob.

I'm getting some confusing info, maybe my meter isn't fast enough to keep up.

SCENARIO #1: When using ISTA : Terminal 50E reads 11.8 V when pressing start and terminal 50L reads 53 Amps

SCENARIO #2: However, when I read the battery Voltage at the starter solenoid connection voltage seems to drop to zero. Also not reading any current draw off the battery.

Measure at starter : 12+ volts, drops to 0
Measure at the jump location of B+, 12+ volts, drops to 11.85V

Does this mean anything or does ISTA Terminal 50E and 50L tell me all I need to know?


The ISTA test procedures says to read at battery and if SCENARIO #2 occurs, replace the CAS module as shown below.................


HERE IS SCENARIO #2 ISTA Test below

Step 1
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Step 2
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Step 3

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This is I'm measuring for SCENARIO #2

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Discussion starter · #23 · (Edited)
Still waiting on removing the plenums and measuring the B+ wires on the starter itself as mentioned before.

Anyhow, mmm back to your waste time method "kidding", repeat the test above, in the second picture choose YES, let see how the result outcomes.
Plenums off, measuring here: Voltage drops to 0.6V when start is pushed. This is between this point (blue) and ground.
If I measure from this point (blue arrow) to the battery jump connection (the positive side of where you charge the battery), it measures 0 volts and when I push the start button it measures 11volts. (my battery is a little run down from testing)
Which one should I be measuring?

I'm not finding loose battery cables.

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WHEN MEASURING BETWEEN THIS POINT and Ground, voltage only drops to 11.85. BTW - how do you remove that little black bolt cover that is shaped like a nut/bolt. It is 17mm in size, and covers the battery cable connection where the arrow points?


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Discussion starter · #25 ·
How about the braided wire down below in the picture when you push the start button what does it read before and after you push the button?
I forget now, car is not where I live, so I can't run out there and get it real quick. How should I be taking these measurements?

#1 or # 2 (or both) ?


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Discussion starter · #27 ·
You've already found the issue. The solenoid top cable should not drop to zero when starter is enabled. Remove that cable and clean the terminal and tighten that nut again. Do the same on the other end of the wire, which from memory is the black plastic nut where you measured 11.85V. That black plastic nut is really a nut. Use a wrench and get it off.

If memory is wrong then that cable goes to the alternator itself but I don't think that's right...
Thank you, everything looks very clean, no corrosion, but I will do that. Even the braided wire is shiny copper. And thanks for the black nut answer! Its on there pretty tight, didn't want to break anything.

What should be the reference for measuring these voltages? Should it be between solenoid top cable and ground?
 
Discussion starter · #29 ·
Measure the top B+ in the picture to chassis, you should read 12V at all time (battery voltage).
Put the meter on the braided wire and to chassis and measure then push the start up button and measure.
Ok, will measure braided wire. I think what is happening, is when I push the start button, I hear a plunger or something move. When it moves, voltage drops to zero. So something must be short circuiting to ground at that point?? What would that be? And why does voltage not drop to zero at other points along that same circuit?

(I have video recording of plunger sound if that helps)
 
Discussion starter · #31 ·
I've tried a few whacks, but haven't moved cable housing out of the way yet to give it a really good whack. So far, the whack has been on the top of the starter. I put a pipe on the starter, then whacked pipe with hammer. Wonder if turning the engine might help as well?

Also, yes, put my 545 battery into the M6 and still no crank - same results.

It looks to me that the 12V B+ on starter travels directly from starter to the jump location (left side shock tower). If I remove one of the 17mm plastic nuts, it will remove power from 12V B+ at starter. Did I overlook something?
 
Discussion starter · #35 ·
Mystery solved guys! Thanks for all your help!! Turns out a loose bolt at the rear of the battery feed that runs thru the wire housing under the plenum. The bolt that holds the starter branch of B+ was loose inside the housing (platti - yes, it was me that removed some of those connectors, I had started taking the wiring apart last night so I could look thru all of it).

The measurements taken at the starter before finding this were:

Starter B+ = 0V when start button pushed, 12.2 V when not pushed
Starter braided wire below = 0.65 V when start button pushed, 0 V when not pushed.

The cable must have been just loose enough to not allow current to flow

The old girl even fired up for about 5 seconds before her computers realized all the connectors were off. She is wanting to go somewhere. Oh how I missed the sweet sound of her S85 !!

Thanks Guys!!
 
Discussion starter · #37 ·
It is not uncommon for that connection to get loose, I am sure this case is the second one , that was the next to check but you were late on measuring the braided wire which will confirm the current isn't flowing and that take the starter from the equation temporary since it is not supplied with B+ enough juice under load demand, just like weak or dead battery, but you confirmed battery is not the issue.

The solenoid isolates the high current from attacking the startup circuit.
In hindsight, mean measuring the voltage upstream of the starter, it wasn't interrupted by the break in the circuit, which is why it didn't go to zero - that was a big clue. I'm blaming the loose bolt on the guys who replaced the starter (if they did, and I see evidence they did). I've put about 2500 miles on the car since I bought it. It should not have come loose that fast.

Thanks again for the help! No fun having a perfectly good working machine stop working and not knowing how much work you may have ahead. My garage is built for planned downtime, not unplanned downtime!
 
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