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How I Fastened a Parasitic Drain on my Automobile in 408 Days

How I Fastened a Parasitic Drain on my Automobile in 408 Days

2023-04-10 10:40:42

10 April, 2023

I nearly misplaced my thoughts fixing a persistent battery drain on my 2013 Mazda3 hatchback. I need to share how I fastened my automobile in case it helps you repair an identical downside.

Quick model: I manually disconnected the important thing fob pc system to cease the battery from draining.

Discovering the Parasitic Drain

My automobile battery would drain itself in a matter of hours or days beginning in January 2022 till I fastened the problem in March 2023. This type of unchecked battery drain—the place your automobile doesn’t have sufficient energy to start out itself after its parked for a short while—is typically known as a parasitic drain.

To diagnose the drain, I parked and locked my automobile. Then, I measured voltages across some of the exposed fuses in my car. The concept is to search out parts within the automobile which might be drawing energy when the automobile is off. A number of fuses confirmed fixed energy consumption together with the TCM Transaxle management system fuse:


Utilizing a lookup table for my brand of fuses, I transformed the 0.9mV voltage on TCM right into a present draw. My automobile drew vital present over 4 fuses even when it was off:

Fuse Description Compartment Present
TCM 15A – Transaxle management system engine 0.9mV -> 197mA
ENG+B 10A – Engine Management System engine 0.2mV -> 27mA
ROOM 15A – Overhead lights engine 0.4mV -> 87mA
ESCL 15A – [Electric Steering Wheel Lock] interior left 0.4mV -> 87mA

In line with one mechanic who labored on my automobile, the overall draw on my 2013 Mazda3 ought to be 50mA or much less when the automobile is parked and locked. So, the 197mA to the transmission pc (TCM) was particularly troubling. Why would the transmission pc stay on when the automobile was parked and locked, in any case?

When my automobile fist began dying in Februrary 2022, the important thing fobs began malfunctioning. Typically once I tried to make use of a fob, the automobile would sound warning chirps for ~10 seconds. Paranoid the important thing fobs have been inflicting the drain, I hadn’t used the fobs for the reason that automobile first died. I had eliminated the batteries from the fobs, and solely used my steel backup key.

Now over a yr later, I guessed that the keyless system was nonetheless malfunctioning regardless that I wasn’t utilizing the fobs. Maybe, the automobile thought a key fob was current within the automobile, and it was conserving programs like its transmission pc (TCM) switched on endlessly by mistake.

The Repair

One of many keyless troubleshooting sections in the workshop manual talked about the ENG+B, ROOM, and ESCL fuses might be associated to keyless system malfunctions. Since I’d additionally seen energy going over thoses fuses, it appeared believable that the keyless system was nonetheless appearing up.

I used to be already solely utilizing my steel key and never the fobs, so I had nothing to lose. I opened up the sprint behind the glove compartment to see if I may disable the important thing fob system straight. After disconnecting my automobile’s destructive battery cable, I unplugged wiring harness 4 from the keyless control module:


Wiring harness 4 is sort of completely communications traces to the completely different radio antennas and switches that comprise the keyless system.

After unplugging wiring harness 4, the instrument cluster now confirmed a purple warning gentle that keyless system was malfunctioning (what I needed):


Once I drive the automobile, I see the purple keyless system warning gentle. Nevertheless, once I park the automobile and lock it, the TCM fuse (and the others) fall asleep and cease drawing energy over the course of a number of minutes. My automobile now not dies after a day or two of sitting. Success!


Why did you nearly lose your thoughts?

  • I think the drain was intermittent: generally the automobile would fall asleep correctly, and generally it wouldn’t. Intermittency made the issue onerous to diagnose.
  • Additionally, two actual mechanics informed me my automobile didn’t have a parasitic draw.

What did the actual mechanics say?

Totally different mechanics informed me completely different tales:

  • Vendor: mentioned my automobile was effective and returned it to me. My automobile died the following morning.
  • Second mechanic: mentioned my battery was degraded, and low voltages from the battery have been freaking out the keyless sytem.
    • Certainly, the automobile lasted 12 months downside free on a brand new battery earlier than it began dying once more.
    • (I nonetheless was solely utilizing my steel backup key, and had eliminated the batteries from the fobs.)
    • A second new battery didn’t repair the problem when the issue resurfaced after the 12 months.

Why did it take so lengthy to repair?

I believe it was as a result of the issue was intermittent. See the complete timeline on the finish of this submit.

Is your automobile nonetheless secure to drive?

So far as I can inform, sure. The #4 cable I disconnected only makes connections to the keyless system, and the one warning gentle is a purple one indicating the keyless system isn’t working (anticipated). All different programs appear to be working usually. You need to most likely seek the advice of an precise mechanic for those who’re contemplating this alteration, although.

If the parasitic draw is intermittent, how are you aware you fastened it?

All of the proof I’ve factors to the keyless system: key fobs malfunctioning, measuring the attracts on the identical fuses in each Feb 2022 and Mar 2023, and the implication of some of the related fuses from the workshop manual that talked about the ENG+B, ROOM, and ESCL fuses. My automobile additionally hasn’t died once more but.

What errors did you make troubleshooting the draw?

Too many to depend. Most essential is to verify your automobile is locked with the doorways closed earlier than you run any experiemnts to search for parasitic attracts. Vehicles can take some time to fall asleep.

See Also

Did you utilize a diagnostic code reader to search for errors logged by the automobile?

No, I most likely ought to have. Typically I needed to fake the issue didn’t exist greater than I needed to repair it.

May you could have disabled the keyless module in software program?

It seems prefer it’s possible to “disable” the keyless module in software. It’s potential this could have resolved the problem as nicely, however I don’t know. Since I don’t have Mazda’s proprieratry M-MDS diagnostic software, I couldn’t disable the keyless module in software program myself.

How did you obtain the Mazda3 2013 workshop guide?

I used this site for the workshop guide.

What different parasitic drain posts did you learn?

I learn a lot of discussion board threads about parasitic drains. One widespread theme was defective bluetooth modules:

How did you take away the glove compartment to entry the keyless management module?

Though it’s about changing a blower motor, the beginning of this video is an efficient information for entering into the sprint.

Did you could have assist?

Sure, loads. Many due to my older brother, Steve, and my Dad.

Drawback Timeline:

Date Standing
Jan 31 2022 Automobile begins dying.
Feb 2022 Key fob is appearing up.
Feb 2022 Vendor says automobile has no parasitic draw.
Feb 2022 Automobile dies day after supplier returns it.
Feb 2022 Absolutely disassemble key fobs (take away batteries). Solely use steel backup key.
Feb 2022 Self diagnose parasitc draw on TCM fuse (and others).
Feb 2022 Get new mechanic.
Feb 2022 New mechanic says I simply want a brand new battery. “Low voltage out of your degraded battery makes the keyless system malfunction and drain your automobile.”
Feb 2022 Get new battery.
Automobile stops dying for ~11 months. (Key fobs nonetheless disassembled. I’m solely utilizing steel backup key.)
Jan 2023 Drawback resurfaces.
Jan 2023 Get one other new battery. (“The chilly winter temperature most likely killed the battery”).
Feb 2023 Automobile continues to die in a single day.
Feb 2023 “If I ignore the issue, it’s going to go away.”
Mar 2023 Observe similar draw on TCM fuse (and others) that I noticed earlier yr.
Mar 15 2023 Disconnect keyless system.
Apr 9 2023 Automobile begins effective after 10 days parked.

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