Saturday, February 6, 2021

Sparky Time, Again

The battery on Rabbit Season, my R1200RS, was going flat awfully quickly compared to my usual expectations and compared to my other bikes. This might usually be a sign of an old, weak battery, but in this case I had recently replaced the battery with a brand new LiFePO4 unit, at the same time as I did on Scooty-Puff Sr.

So I set out to do a bit of diagnostics. I hooked up my DMM in series with the negative terminal on the battery and poked and prodded at the bike to see if I could get it to draw too much current. But, no matter what I did, the current draw would always drop down to 200µA after a few seconds, which was far too little to be able to drain the battery in less than a year or two.

I consulted with the hive mind and did a little thinking and eventually decided that the most likely cause was an internal leakage inside the battery that was draining it between rides. I took the battery back for a warranty exchange and when the clerk told me they needed to run their own tests to check and see if the battery was faulty I prepared myself for them to do only a cursory examination and claim that there was nothing wrong.

Surprise, surprise when a few days later I called back and they confirmed that the battery was faulty and they would give me a replacement. Nice!

Now I just have to wait another month to see if the new battery suffers the same fate. Here's hoping it stays strong!

But on to part 2, the PedoVan, my 2007 Dodge Sprinter. (I'm mentioning the actual models here for the sake of future Google searches by other people suffering the same issues)

I've been having intermittent starting issues with it that seem to be completely unrelated to the battery's state of charge, given that I'd progressed through installing a solar panel float charger, hooking up a plug-in battery tender, etc etc without any luck in addressing the issue.

The basic symptom is that I'll put the key in and turn the van on, and everything comes to life, but when I try to actually start the car I'll just get a click if I'm lucky and then nothing happens. If I turn the van off, wait a few seconds and turn it on again it'll start right up no problem. In fact if I just go back and forth turning the van completely off and starting it again back-to-back-to-back it'll start perfectly maybe 2/3 of the time, and completely refuse to start the other third.

Consulting the hive mind, the usual suspects for Sprinter starting problems are either the Y cable getting crusty and burned out, or the ECU relay misbehaving. It's labeled R7 on this diagram of the under-dash fuse/relay board.

What nobody ever bothers to tell you, though, is the model number of the relay. It's A0025422619, often written A 002 542 26 19. It's a fairly generic Mercedes multi-purpose relay.

I ordered a replacement and I have some small amount of hope that it'll fix the issue I'm having, but I'm not 100% convinced that it'll do the trick. I pulled the relay out to do some diagnostics on it and I couldn't reproduce any issues in isolation, so there's a reasonable chance that there's something in the wiring that's gotten corroded or chafed or whatever.

The good news, at least, is that there's little chance of the ECU being faulty. It's apparently a very robust unit and not prone to failing.

If nothing else, I'll have spent $12 and a little bit of my time to end up with a spare relay, which isn't the worst outcome. But hopefully this solves the problem.

Update: problem not solved, but at least one candidate eliminated.

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