2009 Mazda5 - Parasitic current drain of 290 mA - Solved

#35

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2009 Mazda 5 GT - 5-speed MT
Hello all -

For the last few years I've been running an onboard charger(NOCO Genius 1100), plugging it in when I think of it, fairly frequently in the winter. Because the use of the charger may have been masking the high dark current for awhile, it's hard to say when the problem started. In any case the battery has been flat a couple of times in recent weeks.

The first time I figured it was because the car had been laid up with some driveline problems which took me a few weeks to sort out, but the second time I thought I'd better dig in and find out what was going on.

First of all, I suspected the battery, even though it's an AGM and only 2-1/2 years old. I charged it up fully, and then did a load test. The battery passed fine.

Then I removed the -ve battery cable, and hooked up an ammeter in series with the -ve battery cable and post. Yikes - 290 mA! (0.29 A on the 10 A setting on my DMM.) That's way too high for dark current, which I expected to be no more than about 50 mA.

I started by unbolting the cable from the battery to the main fuse panel under the hood. Yup, that killed the dark current draw completely - 290 mA -> 0 mA immediately. OK, so it's something run off the main fuse panel - start pulling fuses, and relays if necessary. Pulling the 15 A ROOM fuse did the trick - again, the dark current dropped to 0.

Now for some research - uh oh, the ROOM fuse supplies many things! Checked and rechecked the most likely culprits, the interior lights, but they were definitely not staying on. Went down a few rabbit holes, including wondering if the security system was drawing excessive current.

Did some research online, and found many threads, most of them inconclusive. Wondered about the factory radio, although the defective sound systems all seemed to be aftermarket.

Broke out the schematics, and was disheartened to find that the ROOM fuse feeds the Body Control Module (BCM). Gah!

Just because, I removed all of the fuses from the secondary fuse panel (located in the R side of the dash, facing the passenger door). No change in dark current.

Back to the internet, where one "Ask The Mechanic" Mazda tech had recommended that the parasitic current draw on the questioner's Mazda CX-9 was likely caused by the Bluetooth (hands-free) unit.

With little to lose, I removed the glove-box door, reached up through the cavity, and, with some difficulty, removed the connector to the Bluetooth unit. (Confusingly enough, this doesn't appear as such in the Mazda 5 wiring diagrams, but may be called, in Mazdaspeak, the "Data Link Connector". (Or not - I could be wrong about this.)

But in any case, that solved the problem - the dark current quickly dropped to 130 mA, and then to 20 mA as things went to sleep.

It's no hardship for us - we have never used the Bluetooth, and I guess now we won't.

I hope this helps someone else - given that similar happened in a CX-9, I would bet you'd see similar in other Mazdas of this age.
 
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South Carolina
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12 MZ5 13 CX-5
Not sure about your exact model, but I believe that some Mazda's have had TSB's about faulty Bluetooth modules. Yours may be effected as well.
 

#35

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2009 Mazda 5 GT - 5-speed MT
Not sure about your exact model, but I believe that some Mazda's have had TSB's about faulty Bluetooth modules. Yours may be effected as well.
Do you know if the Bluetooth module is covered by some sort of extended warranty as a result of the TSB? It's not a big deal as we've never used it, but but I would get it replaced if there were no cost involved.
 
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South Carolina
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12 MZ5 13 CX-5
No clue about that. Very generally speaking, TSB's are just notices that if something's wrong, here's where to look. It's not like a recall at all. It's more of a guideline, and if that part has indeed failed, here's how to fix it.

Personally, I replaced my factory stereo with a Kenwood with Android Auto. Cheaper fix, and much, much happier now.