Wake up!

Andrew Diagnostician Georgia Posted   Latest   Edited  

Hey smart people,

This is a general theory question to expand my understanding hopefully. I know we have all dealt with parasitic draws, and it happens even more as they get more complicated. Ive done a bunch of these myself, and I find many times that a module is the cause of the draw because it “Wakes up” and asks for status updates from all the other modules on its network or sometimes on every network. I've seen things like inductive door handles on a BMW telling the antitheft module that someone is trying to open a door so it triggers a key code request and then goes back to sleep. Well, if that happens enough the battery dies. 

So, my real question is this: What kinds of inputs can cause a module to wake up, and is there any sense as to how or why they will respond? My example is this, a ford fusion has a bad TPMS module that is waking up the whole car and causing a draw. What kind of input could it be receiving to cause this? Or, Is this an internal fault that causes the module to wake?

I'm looking forward to your thoughts.

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Caleb Diagnostician
Indiana
Caleb
   

What year is the Fusion? Does it have any hardwired inputs to the TPMS module? Can you post a schematic of the TPMS module? You could depin the CAN lines at the TPMS module and reconnect. If the draw is still there it's likely an internal fault. But need to check any hardwired inputs into the module before condemning it. Example, had a 14 Escape one time that the IPC kept waking up the network…

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Glenn Owner/Technician
Texas
Glenn
 

Hello Andrew, One of the most common “wake up" issues I see is when people leave a device plugged in to the power port of the vehicle. Need more info on your vehicle. What else is on the TPMS circuit?

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Geoff Diagnostician
Hawaii
Geoff
   

"What kinds of inputs can cause a module to wake up, and is there any sense as to how or why they will respond? " Depends on whether the module is BROKEN or not. :-) Too many manufacturers and too many system designs to make any broad statements. Sometimes, at least, if you read the network operation theory in SI, you can at least figure out if the modules get a discreet wake-up signal (like…

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Phil Technician
Nevada
Phil
 

I had a 2018 Jeep Renegade with a 2 amp draw. The ABS control module was staying awake. The amperage would fluctuate between 300MA to 2 amps. The electric parking brake switch is hardwired to the ABS module. I detached the connector from the switch. The switch and connector had green corrosion. Voltage was bleeding across the switch terminals. This was causing the draw. Most of the time I have…

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David Diagnostician
Georgia
David
   

When dealing with parasitic draw issues I have found that sticking to the OEM procedures for diagnosing have saved me a TON of time. I once worked on a 2017 Honda Accord with a Parasitic draw, and one of the first things the procedure directed, is to make sure the security light is on in the dash after securing the vehicle. Turned out, It was not on and when checking the feedback from the…

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Geoff Diagnostician
Hawaii
Geoff
 

David, I was unaware any manufacturers wrote procedure for this into SI. I have seen a TSB once or twice, ever. With so many different terms (draw, drain, key-off current, etc) how do you find it in SI? Just search everything with "battery" in it?

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Andrew Diagnostician
Georgia
Andrew Update
 

This is great! Thanks so much for the replies. I don't have an actual ford fusion that I'm working on. It was an example from Sean Tipping's Automotive Diagnostic Podcast but is still relevant. I like the button input ideas. It seems like a large number of the examples you guys put up are related to a discreet signal into a module, which makes sense, especially with modules that stay active…

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Chris Technical Support Specialist
New York
Chris
 

Once the draw is isolated to a module, looking at inputs with either data or wiring tests would be recommended before condemning the module.

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Timothy Owner/Technician
Wisconsin
Timothy
 

Usually, if you fell that it's a module, you can short the CAN lines together and the modules will go to sleep, as the whole system is down. Of course, it won't do alot for the non-CAN systems, but, at times, shorting those lines can also shut down errant modules.

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David Diagnostician
Georgia
David
 

If you hook up a scan tool to the body module and look up the appropriate sub menu for the items in question, you can see the current state of the input in question. If it is opposite of the expected position, that is usually a tell.

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Andrew Diagnostician
Georgia
Andrew Resolution
 

Thanks so much for the input. There is lots to think on here. Andrew

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