Can someone proof read this for me?

Richard Diagnostician Alberta Posted   Latest  

At my shop, we use Slack for communication. I created a tech tips channel where technicians can share “how did I fix that” type of stuff. I like to post case studies and diagnostic strategies. I have written an introduction to battery draw testing, would you ladies and gentlemen be able to proofread this and make sure I'm not out to lunch on anything. If I'm technically incorrect on anything or if I should add or subtract something, I would like to know about it. My audience is a bunch of 20-30-year-olds who I'd say have an above-average skill level for being in the trade for less than 10 years but lack diagnostic ability.

How long should a 12v vehicle battery last?

The complaint may be that the battery is stone dead after the vehicle has sat for a few days, or the owner has had to put a new battery in every year for the last few years. How do you solve this problem? Where do you start?

Every vehicle will have a parasitic draw or depending on the manufacturer nomenclature, a quiescent draw or whatever they want to call it. This is the power that gets used to keep vehicle memory, clocks, and let the vehicle keep in touch with the outside world. The larger the vehicle's electrical architecture, the larger the draw will be. The engineers that designed the electrical system in the vehicle, size the battery’s reserves capacity to the amount of draw that the vehicle has. If this draw is too high, you start killing batteries. 

Do you have a problem? Most manufacturers will publish a max draw spec. Search battery draw in service information, sometimes Alldata/Mitchell does not have a spec so we have to go off a rule of thumb number. I have found most specs are around 30mA. Right now, we have one hour of diagnostic time. We are going to use it to find out if we have a problem or not. Battery draws generally take a few hours to solve so we have to come up with a game plan. I always start with a full vehicle code scan and find out what systems have set what trouble codes; I will give the list a quick scan but take pictures of the codes and save them for later. While I have the scan tool plugged into the vehicle, I will run an energy report, depending on the vehicle and our scan tool capability we may or may not have this information available to us. If we do, the report will tell us how the vehicle has been driven over the last 30 days or so and if any systems have been using more power than normal or not entering sleep status. I will also take pictures of the report. I will take the vehicle for a 15-minute test drive, during the drive I want to use every device on the vehicle possible. Turn on the wipers, the lights, the AC, heated seats and steering wheels, windows, stereo, basically any accessories in the vehicle. I will pull it into my bay and prepare it for a draw test. Locate the battery, find out how all of the doors, hood, trunk/liftgate are monitored and fool the switches/potentiometers to represent the closed position. Connect your Amp meter in series in-between the positive battery post and the positive battery cable, remove the key from the vehicle and let it sit for at least 45 minutes to an hour so all of the networks go to asleep. Clock onto another job for these 45 minutes. After everything has gone to sleep, take a look at your Amp meter. This is your battery draw. On the work order, note everything you did including all measured values and their specs.

If the draw is out of spec, you will most likely receive another two hours or so. Our objective right now is to find a direction and start chasing the draw. We have to decide if the draw is coming from a network problem or a power distribution problem. The trouble codes and the energy report should help with this. But you also may not have that info available to you. Clock back onto the job, go to the service information and pull up a power distribution diagram, identify all of the fuse boxes and their locations. Next, find a computer communication diagram. Identify all of the communication networks. Find a gateway module that you can access all networks from. Go to the vehicle and create access to the fuse boxes and the chosen gateway. Connect your Amp meter to the battery and let the vehicle go into sleep status again. I usually start on the communication side, grab your scope and one by one back probe the high and low lines of each network. There should not be any binary code. If there is, the network is still awake (most of the time). Access that network's splice pack and disconnect each module one by one until the network enters sleep status. Once you find the offending module you now have to diagnose why it is keeping the network alive, it could be a bad module itself or an input that is keeping it awake. Once the networks are all asleep check your Amp meter on the battery, is your draw under max spec?

If all of the networks are asleep, we move on to power distribution. The old-school method of pulling fuses until the draw disappears is not going to work. When you remove a fuse, you remove power from that circuit. When you install the fuse, you energize the circuit. If that circuit powers a module, it will power up and broadcast an “I’m here" message on its network waking everyone up. You now get to wait 45 minutes for everything to enter sleep status again. We need a better way to find out what circuits are drawing power. Using ohm's law, every electrical connection will have some resistance. When you measure the voltage drop through a resister, the more current flowing will result in a higher voltage drop. Fuses are an excellent place to test this. On the top of spade/blade fuses, there are two little metal nubs on either side of the Amp rating. Measure the voltage drop in millivolts in-between these nubs on every fuse in every fuse box. The higher the voltage drop, the more current that circuit is using. It will take about 15 minutes to clear a fuse box, you will be checking a few hundred fuses. Whenever you get a fuse that has more than 1 millivolt drop, mark it with a sharpie. Once all fuse boxes have been checked, write down what fuses in what boxes have a draw on them. Find each fuse in the appropriate wiring diagram and find out what those circuits do. At this point, you should have a few hours clocked on this job. Every hour I spend on the vehicle I will stop and fill out the notes on the work order. I will write down all of the tests that I did and the values that I got. I will then re-read all of my notes and sit back and evaluate and make sure I’m going down a logical path to solving this problem.

Now that I have found what circuits are drawing power. We have to find out what circuits are supposed to be drawing and what ones are not. Things like navigation, telematics/V2X, and radio frequency antennas allow the vehicle to contact the outside world will normally draw power. Body control modules will also generally have normal draw. You are looking for things like wiper motor circuits, lighting, any seat or window system. Read through the description and operation for each one of these systems in our service information and find out if they are meant to draw power or not. Once you have identified some circuits that you think should not be drawing power, then pull that fuse and see what your battery draw is at. You may wake up a network a few times, but once you get the right circuit your draw will drop to under 30mA. This is generally where you will find all of the aftermarket stuff installed in the vehicle. When these systems get installed, people will tap into whatever power they can find or a wire close by that has 12 volts on it and may not actually know what that wire does. Things like alarm/remote start systems should not be drawing over 30mA, I have found when an alarm system fails it will draw like 900mA. When you locate the circuit that is drawing power you now have to diagnose what is happening. A by-product of current consumption is heat. Things like jammed wiper motors that cannot get into the park position will be warm/hot to the touch. Same thing with any inductors like motors, alternators, solenoids or relays. Remove components out of the circuit until you find what is causing the draw.

I hope the brief overview helps sharpen your diagnostic skills. I have left many things out as every vehicle/manufacture is different, but when you come up with a plan and apply the laws of electricity and study hard there isn’t a problem that you cannot solve.

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Interesting
Jonathan Technician
California
Jonathan
 

I was always told to draw test from the negative/ground side of the battery. Not sure if that has changed.

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Rudy Technician
Utah
Rudy
 

Jonathan- Current flow is the same through both negative and positive sides of the battery. It doesn't matter which side the test is performed on, the results will be the same.

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Joe Owner
California
Joe
   

I will be happy to review it. I am a retired Langevin Certified Instructional Designer/Developer for a major OEM. Give me a couple of days as it is very wordy. The rule is “Less is More”!

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Benjamin Diagnostician
Connecticut
Benjamin
 

In addition to my experience as a Toyota/Lexus, I've been freelance writing since 2012 for several automotive companies, such as NAPA and The Hybrid Shop. PM me for a quote on a professional rewrite.

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Funny
Richard Diagnostician
Alberta
Richard
 

Oh, this is just some stuff I will put together on my free time to help out the younger technicians that I work with. Thank you for the offer!

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Andrew Mechanic
Michigan
Andrew
 

I though it was good. I liked your method of writing everything down and then taking a pause and looking back through the data in a logical fashion.

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Thanks
Jeff Technician
California
Jeff
   

IMHO way to time consuming, In my 50 years in the business I never got 3 hours to diag anything. If the battery went dead there would likely be no useful codes stored, I would scan only if a light was on. I would use a thermal camera to check the fuses, if no obvious issues I'd check each individual fuse, then if a issue showed up grab a diagram and go from there. each time you remove and…

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Richard Diagnostician
Alberta
Richard
 

That is great! I will add a thing about the starting with a good battery/charging system, totally forgot about that. We work on mostly European and exotic stuff, most of the customers don't care how many hours it takes they just want it fixed.

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Jeff Technician
California
Jeff
 

Most learning from your stuff won't be that lucky.

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Justin Technician
California
Justin
 

I start with 1.5 hours and if it’s intermittent give customer options . I charge for my time . Too many cars in the all makes all models scene to wait for another pattern failure one to come along to make up for lost time .

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Justin Technician
California
Justin
 

What scan tool can look at energy consumption?

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Bill Owner/Technician
Michigan
Bill
 

ISTA & ODIS (BMW, VW, Audi) i suspect others too but these are only examples of what tools I have that can do energy consumption.

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Jeffrey Mobile Technician
Illinois
Jeffrey
 

Honda I believe has some data. Haven’t messed around with it since John Thornton told me about it in a class!

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Marty Technician
California
Marty
 

Mercedes, most models from 2009 on

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Bill Owner/Technician
Michigan
Bill
 

Jeff I have to disagree with this comment -"If the battery went dead there would likely be no useful codes stored" codes don't just disappear on modern vehicles when the battery goes dead…. I often find clues such as convenience entry door handle circuit faults

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Helpful
Jeffrey Mobile Technician
Illinois
Jeffrey
 

So the way I perform parasitic draws is a little different. I’ll go through some typical draws I have dealt with and you can see what you like or don’t. Since I’m mobile, the first couple of steps would be different! I get the phone call from a client, car has a draw, I ask them how long it takes for the battery to die. This will give me a idea as to large or small and how often the vehicle is…

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Randall Owner/Technician
Michigan
Randall
   

I really appreciate the effort at documenting a process for parasitic draw. Lot of good comments and content. My only contribution would be that I will try and condense all this content in this thread, down to a one page checklist. Then we will do a zoom recording with my techs discussing the content and checklist, for future reference and new technicians that may find a home at our shop in the…

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Mike Owner/Technician
Alberta
Mike
 

Wow. Such an excellent post. Thank you to the contributors and to Diagnostic Network for making this possible. Reminds me of what IATN once was.

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Rudy Technician
Utah
Rudy
   

Richard- I feel like to really get your point across to the younger generation, you should use bullet points to highlight most important info and condense the rest of your theory from there. Also,It doesnt matter which side the draw is measured from(positive or negative) your write-up seems to indicate otherwise. On a side note, I still pull fuses. Much easier to pull 75 different mini/micro…

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Joe Owner
California
Joe
 

Hi Richard, I am in the process of turning your procedure into a check list with all of your points which requires minimal reading. Hang in there, I will have it to you on Monday at NO CHARGE! Great information!

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Thanks
Richard Diagnostician
Alberta
Richard
 

Some of you have suggested using bullet points or keeping it short. I agree. I find using PowerPoint for simpler things works well, but it is hard to put the “why” and “how does this work” into a few sentences. I have created PowerPoints on what is a scope and its basic functions and simpler diagnostics, they went over well. Whenever I create some sort of write-up, or we go to a training…

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Joe Owner
California
Joe
 

Hi Richard, Here is what I have put together as a checklist for checking Parasitic Draw using the information you provided. I added the use of a Jumper Box to reduce accidentally disconnecting the battery cable and having to wait for everything to go to sleep. It is a PDF. I can send you the word doc file if you want to make any corrections or changes. joe

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Richard Diagnostician
Alberta
Richard
 

Thank you for doing that! I like the format. Much appreciated.

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Travis Diagnostician
Texas
Travis
 

20-30 year old techs won’t be interested in reading that whole thing. Work on condensing way down to more like bullet points.

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Richard Diagnostician
Alberta
Richard
 

I remember reading for hours trying to wrap my head around something in my 20's. Something I still do in my 30's.

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Travis Diagnostician
Texas
Travis
 

I just think most techs out there that I’ve worked with don’t invest that much in themselves. The guys on this group are probably the exceptions.

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