Буду дуже вдячний за будь-яку пораду 🙏
[img alt="I’m attaching some photos from the scanner.
I’m not a professional mechanic, but I really like working on this car."]https://cimg8.ibsrv.net/gimg/www.mbworld.org-vbulletin/2000x1504/img_9908_cc3cd35c97f664b1845dc506e790fe623613d79f. jpeg[/img] I’m attaching some photos from the scanner. I’m not a professional mechanic, but I really like working on this car.
You are dealing with what looks like a qualified poor voltage control.
Your hands-on survey reveals a voltage related fault plus shows roller coaster voltage extremely high.
ECU voltage !!!!
The key is what is causing that mess??
A handful of items are qualified to introduce odd results.
You can pull a diagram of ECU Power lines and research where voltage gets affected.
DIY'ers have limited interest to work down a busy test list for free.
voltage rodeo: 22V High/ 6V Low !!!
This Pm I've met with some Mayan local powers... 🤿
The evidence of voltage swings are revealing...Today it's not the garden variety Yoyo.
This is special:
From normal 12V battery voltage
up to 22V and
down to 6V
says that the voltage reference is jacked up.
Any seasoned battery may produce 6V brown-outs to crash CAN nodes.
Here in addition we are seeing TWENTY TWO+ VOLTS... Thats special!
Alternator can not make that kind of voltage even on a bad day (unless battery is hardly connected to load down ALT output).
I believe we are looking at a version of bad GND:
Bad ECU painter GND posts ?
Bad single main GND strap undercarriage ?
ALT is directly attached to engine therefore 95% chance it has good GND for itself!
This brings us to the issue being between ALT and ECU on the GND side I believe.
The high current load drop-voltage is what's creating the fake 22V ECU is seeing.
12V batt + 10V drop = 22V.
So that is likely referring to a salted main GND strap.
Let's measure that and go from there.
You are dealing with what looks like a qualified poor voltage control.
Your hands-on survey reveals a voltage related fault plus shows roller coaster voltage extremely high.
ECU voltage !!!!
The key is what is causing that mess??
A handful of items are qualified to introduce odd results.
You can pull a diagram of ECU Power lines and research where voltage gets affected.
DIY'ers have limited interest to work down a busy test list.
voltage rodeo: 22V High/ 6V Low !!!
This Pm I've met with some Mayan local powers... 🤿
The evidence of voltage swings are revealing...Today it's not the garden variety Yoyo.
This is special:
From normal 12V battery voltage
up to 22V and
down to 6V
says that the voltage reference is jacked up.
Any seasoned battery may produce 6V brown-outs to crash CAN nodes.
Here in addition we are seeing TWENTY TWO+ VOLTS... Thats special!
Alternator can not make that kind of voltage even on a bad day (unless battery is hardly connected to load down ALT output).
I’ve never really worked with electrical systems before, but I want to understand it and figure it out.
What do I need for this, and does anyone know where I can find these wiring diagrams?The voltage was showing 11.4V with the engine off and the ignition on.
I spent a long time trying to find the problem using the scanner, and I ended up draining the new battery.
I’ve never really worked with electrical systems before, but I want to understand it and figure it out.
What do I need for this, and does anyone know where I can find these wiring diagrams?The voltage was showing 11.4V with the engine off and the ignition on.
I spent a long time trying to find the problem using the scanner, and I ended up draining the new battery.
The battery is AGM.
You're in the right place! Let's keep this practical and quick!
Your car was designed to a predictable ownership course.
tackling this huge voltage spikes - Great job identifying that non-sense.
> No1 suspect: salted single engine-chassis strap now oxidized.
> Test 01: single strap
measure the voltage between the engine block and the brass GND jumper nut with a DVM WHILE CRANKING
How many volts do you measure: 1V or 10V ??
> Test 02: doubled strap
Repeat cranking and meadure same as prior but use a bypass cable in parallel with strap between engine block and Brass GND jump post.
Given that secondary bypass condition, does the ECU still show 22V during crank??
> PLAN B... :
If this does not pan out we'll need to experiment with the positive path dropping:
battery + prefuse path creating drop during crank.
> Besides Note: try to never let your starter battery drain down - A full battery is one with minimal heat dissipation.
You're in the right place! Let's keep this practical and quick!
Your car was designed to a predictable ownership course.
tackling this huge voltage spikes - Great job identifying that non-sense.
> No1 suspect: salted single engine-chassis strap now oxidized.
> Test 01: single strap
measure the voltage between the engine block and the brass GND jumper nut with a DVM WHILE CRANKING
How many volts do you measure: 1V or 10V ??
> Test 02: doubled strap
Repeat cranking and meadure same as prior but use a bypass cable in parallel with strap between engine block and Brass GND jump post.
Given that secondary bypass condition, does the ECU still show 22V during crank??
> PLAN B... :
If this does not pan out we'll need to experiment with the positive path dropping:
battery + prefuse path creating drop during crank.
> Besides Note: try to never let your starter battery drain down - A full battery is one with minimal heat dissipation.
So here is what was done today:
I measured the ground voltage drop — it showed 0.0049V.
Then I checked the voltage drop from the alternator to the battery, and it showed 0.028V.
I also checked the voltage from the battery positive terminal to pin 15 (constant power supply for the ECU) while the engine was running. The voltage drop was between 0–0.2V and it fluctuates a little.
I ran many tests with the help of ChatGPT, and everything looks normal. There doesn’t appear to be any significant voltage drop or bad ground.
I have ordered a new ground cable with the battery sensor, and I want to try replacing it. I also ordered a used throttle body, and once I install it I will try to perform the throttle adaptation and see what happens.
Another thing I’m thinking about — could this possibly be caused by a low-quality or defective battery?
What do you guys think about this?
The ignition is on, but the engine is not running.
When the engine starts, the scanner shows voltage spikes at first, then it stabilizes to normal voltage. But as soon as I press the accelerator pedal, the voltage spikes appear again.
This is the graph when I disconnect the connector from the negative battery terminal sensor and press the accelerator pedal.
After all these tests while trying to find the problem, some new fault codes showed up.
Could this issue be caused by a problem with the engine control module (ECM) or the SAM module?
This is what the SAM module looks like under the cover. I removed all the connectors and checked for corrosion, but I did not find any green corrosion.
Goood coverage: you've got to meet two sleepless VIP's: SAM+CGW - Running 24x7
They don't show evidence of water damage per say but some type of dry whitish residue: flux?
Since you got in the F-SAM tray, then cleanup your unprotected circuit board with isopropyl alcohol+ soft (tooth) brush.
flux is best cleaned off
flux not best ignored
unprotected PCB + Flux... not best practice!
You got to wonder who decides this quality meets MB standards ??
both rows of connectors need cleaning
circuit begin for a cleanup + silicone preotection
Lucky us this module was not selected to use solderless pins.
latest fault collection
> How does that help troubleshoot?
-1-What's clear is there's nothing wrong with your throttle body!!
-2- ECU complains of bad voltage power supply.
Back to chasing the unsettled "high and low" voltages.
This seems fairly limited to the ECU ONLY... no other modules are reporting similar impact.
-- Feel free to use a schematic diagram to map out what ECU pins are seeing bad voltage.
-- Clean up the footwell carpet GND and under cowl cover.
I still believe this is related to the ECU sensing artificially poor GND.
The chassis voltage is mostly correct (12.6V to 14.9V) but the ECU is not referenced to zero commun GND.
The finding may be super significant not only for OP but also for every W212 that has proven to be "voltage sensitive". This should be a great fix, hidden in plain sight.
