Stop/Start system starter current

Bob Technician Massachusetts Posted   Latest   Edited  
Case Study
Driveability
Electrical
2016 Chevrolet Malibu LT 1.5L (T LFV) 6-spd (6T40) — 1G1ZE5ST1GF305438
P3055
P3056
Start/Stop Fault
Auto Start Fault

This car is fixed but I thought I would post this just for the archives. First start/stop starter I have tested and the results were interesting.

The code description is DC/DC Converter Output Voltage 1 Performance and Voltage 2 Performance. A full system scan showed lots of low voltage and communication codes so i decided to test the battery first. I like use a scope to test batteries as it can show you the true voltage drop on initial crank. This dropped under 6 volts at a little over 600 amps. I also noted that the start time was almost 800ms. Published spec for start time is 300ms. Time for a new battery.

With a new battery the voltage dropped to about 8.5 but what was really interesting was that inrush cranking current was 1500 amps. Holy smokes that's a lot but it makes sense since this starter has to get the engine up to running speed in roughly 300ms. As you can see the start time is now 400ms which is about half what it was with the old battery.

Bottom line is that a new AGM battery solved all the issues. A road test found the stop/start system working normally. Nothing spectacular but I thought the scope captures were pretty cool.

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Dmitriy Analyst
Ontario
Dmitriy
   

MORNING EDIT: Bob, I find most interesting in your captures that the ECM can still operate when the battery voltage is 5.7V. Moreover, it set codes for DC-DC converter Output Voltages 1 and 2 being low, but not that the battery voltage is low. It made me think at first that the ECM is also supplied from the output of the DC-DC converter, hence my original reply. However, reading about the…

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William Technician
West Virginia
William
 

Here are the schematics showing what the T19 DC/DC Tranformer powers.

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Dmitriy Analyst
Ontario
Dmitriy
 

Thank you very for the info, William! It turns out the TCM and BCM are fed from the Transformer/Converter, but the ECM only talks to it over data lines.

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Jürgen Owner
Mexico
Jürgen
 

Thank you Bob for this information. Was the new battery of the required characteristics? Asking this because it didn't comply with the cited 300ms.

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Bob Technician
Massachusetts
Bob
 

It was an agm battery at the rated spec. We used an interstate MTX-48 H6 I'm guessing the 300ms is best case scenario. Maybe a little fudge factor for age and mileage? Plus my measurement may not be precise enough for when the engine is actually at running speed. A crank signal or ignition may give a better idea of when the engine is actually running. Next time I'll add that in.

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Geoff Diagnostician
Hawaii
Geoff
 

same question as Jürgen. "spec for start time is 300ms" and now you have 400....so....is 300 just ballpark/nominal?

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Bob Technician
Massachusetts
Bob
 

As I said to Jürgen, my measurement may not be precise enough. I figured since the start time with the new battery was roughly half of the old, it was likely good enough. The car seemed happy with it.

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Geoff Diagnostician
Hawaii
Geoff
 

Thank Bob. Also, ECM never really sees or thinks like we do, anyway :-)

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Timothy Owner/Technician
Wisconsin
Timothy
 

Is an AGM battery what is called out in the parts for this? If not, it might account for some of the anomaly that you're seeing here. Having the absolute same battery as what the OEM wants can make the world of difference. there's a bit of difference between the way current gets delivered from an AGM vs. traditional Lead acid. BMW won't even let you choose different batteries other than what is…

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Al Educator
Ontario
Al
 

Great stuff Bob These are the types of case studies that really hit home with the new technology that we are all learning, sometimes by the seat of our pants. You took the time to look up specs as well as posting this study and this is a great attitude. With your permission, I would like to present this to my class when I am teaching stop/start. Al

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Bob Technician
Massachusetts
Bob
 

Sure Al, I'm glad you liked it. I have learned so much from others who post case studies and such that I like to return the favor when I can and post things that may be interesting or helpful too.

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Bob Technician
Massachusetts
Bob
 

The original was AGM. It's a much more expensive option that we wouldn't use unless it needed it. I agree you should always match the original.

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Brian Technical Support Specialist
Connecticut
Brian
 

Good stuff Bob! Thanks for sharing! On a somewhat related note, did you have to “register” the new battery once you replaced it? Like you do on BMWs. Just curious as I was recently asked this by a customer with a 2017 Malibu, who thought it needed to be done, but couldn't find it in his GDS. TIA

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Bob Technician
Massachusetts
Bob
   

Brian, I looked it up and there is no scan tool function for that. it said that it required the vehicle to sit for at least 3 hours with everything powered down. it appears to be a passive learning function.

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Nathaniel Diagnostician
Ontario
Nathaniel
 

This is great info, and well presented Bob. Thank you! I can see where they describe the starter performance, but it doesn't seem to be a hard-and-fast specification: “The Engine Stop/Start system in GM vehicles automatically turns off the engine when the vehicle comes to a stop under certain driving conditions, and can quickly restart the engine in about 0.3 seconds when commanded to do…

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Tony Owner/Technician
Missouri
Tony
 

Bob, thank you for posting this. What is the max current reading spec of, or more bluntly, what model number amp probe did you use here?

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Louis Owner/Technician
New York
Louis
   

Bob, 8.5 volts @ 1500 amps inrush current doesn't sound right. This would be 5.6 milli ohms (.0056 ohms) electrical resistance from solenoid contact, through brushes, and then through some copper windings. I highly doubt this. If you measure the starter resistance with your milli/micro ohm meter, even neglecting the solenoid contact, and going from armature to case, your milli ohm…

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Rudy Technician
California
Rudy
 

Bob- What did you use to measure 1500 amps?

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Paul Owner/Technician
Illinois
Paul
 

Bob, did you do an all system Network scan before? I have been doing them on all my clients cars and have found few PCM's ever code for a battery issue like Toyota P1604 (as a possibility). However I have found that there are always a few modules that set codes for low battery voltage. When I see those codes, I scope the battery. It's usually a dead give away. But yes, we need to be doing this…

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Bob Technician
Massachusetts
Bob
 

Yes, I uploaded the pdf

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Robert Owner/Technician
Massachusetts
Robert
 

We see a lot of communication codes and intermittent electrical consumer issues on BMW, in body electronics 4, BMW says to perform an energy management diagnosis before trying to solve any of these issues and even applies that theory to drive-ability troubles. If the battery is determined to be below 59 % they say to change it even if it is only 2 years old. Case studies have proved this to…

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Jim Educator
California
Jim
 

Hi Bob What was the batteries SOC when you monitored the voltage drop?

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Bob Technician
Massachusetts
Bob
 

That's a great question Jim and it's a test I should have done but didn't. Looking at the start of one of my scope captures it was definitely low. I did the all module scan and saw many low voltage and communication codes including the dc/dc converter voltage codes. I put the scope on it and saw the low cranking voltage. I inspected the battery and observed that it was the original which made…

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