Slow Start

I have a 2013 Tacoma 4wd that was experiencing extremely slow cranking and start-up. On Thanksgiving day 2023, I replaced a dead battery. Once the slow cranking/starting began a few weeks after replacing the battery, I also replaced the starter with a rebuilt Denso. While the cranking is faster and it starts after a second, it is still slow to turn over compared to what it used to be.

Another weird symptom is that the electric door locks have only half unlocked once or twice. You can hear a slow/weak unlocking/locking sound from the locks, and there have been a couple of times when the door will not unlock completely.

I've also noticed the interior dome lights momentarily dimming when using the door locks too.

I just bought a multimeter and my plan is to do some drop tests between the battery, starter, and alternator. But the dimming lights and intermittent issues with the locks are issues I haven't heard of before.

I'm an electrical virgin and this will be the first time poking around the wiring, fuses, etc.

Are there any ideas of where I should start my investigation? Has anyone had an issue like this before?

Thank you for any help!

 

You had the battery checked .....

 

Check battery voltage at the terminals first. That way you know what you're working with.
You have to check voltage drop underload. So you'll need to be cranking the engine over to check it.
As well as operating the locks and such.

And easy(er) check would be right at the headlights.

Terminal to cable clamp
Terminal to Body
Terminal to component......

 

Alrighty...tested the battery at the terminals and I'm getting 10.72 volts. So, I'm taking it back tomorrow to see if they'll swap it out for me. Hopefully that will solve the issues.

 

Maybe, But you could have a parasitic draw too.
They are going to want to try to charge the battery and test it before swapping it out.
You can't test a battery properly if it isn't 12.6v or more

Might as well do them, and yourself, a favor.
Charge it before taking it in to have it "swapped or tested".

Or check for a draw on the truck first.

 

Maybe the alternator is defective and not charging properly.

Check voltage at the battery when the engine is running and see what it is. It should be over 13.5 VDC.

 

10.72 is with the engine running, not running, or while cranking the starter?

Alternator is my first guess too but more information and probably further testing is needed.

Op, provide us with 3 voltage readings. At the battery with the engine off 1, at the battery the lowest voltage reading while cranking 2, and at the battery with the engine running 3. 3 more would help too. The same previous situations but with the negative lead on battery negative, and the positive lead on the big starter terminal.

 

10.72 was without the engine running.

I took the battery back to Autozone yesterday. They tested and then replaced it. It has solved the issues, but I'm keeping an eye on it in case there is a parasitic draw or alternator issues.