I had that problem too; the battery cables looked fine, even after cleaning up the electrical contact surfaces. After replacing the clamp ends with new, the problem went away. Apparently, some sort of electrical resistance internally of the metal over time. It is after-all, a 20 year old vehicle.

 

I cleaned battery terminal and clamp with metal brush after the first problem also, but apparently it didn't help.
Did you replace clamp ends only (not cable)?

 

Make sure your negative/ground battery cable and all its connections to the frame/metal look clean. Same with positive cable. Haven't done this on a Sienna yet, just years of experience with car electrics in the two-way radio biz and my beater Volvo 240s, well known for wonky grounds. Relay would be my next guess, but a starter on it's final lap(s) is also a strong contender. Good luck!

 

I cleaned battery terminals & clamp, but it didn't help. I didn't do anything with ground connection between battery and the body yet. Seeing ~1V difference on voltage reading at first, my EE feeling is telling me that it could be different GND potential. I will try cleaning the GND cable connection on body frame.

 

For grins, swap the starter relay with the AC relay beside it, assuming AC works as it should.

Sixto
04 LE FWD 240k miles

 

Yes, A/C still works great (compare to my 4 year old Lexus...). Didn't know that A/C & starter relays are swappable. I'll put it on the to do list.

 

Remove the battery and battery platform so you can inspect the ground cable all the way to the frame ground point and the positive cable all the way to the starter terminal. Look for corrosion at or near the terminals and looks for bulges along the insulation. Don't overtighten the starter terminal nut! It doesn't take much force to snap the threaded post. Ask me how I know. Are you in an area where they use road salt?

If you're adventurous, have someone hold the key in start position for a few seconds after the first inadequate engine movement while you feel along the positive and ground cables. Does one feel notably warmer than the other? One warmer cable suggests more resistance in that cable. Watch your hands because the starter might suddenly kick in at full speed while the key is in start position.

Sixto
04 LE FWD 240k miles

 

Remove the battery and battery platform so you can inspect the ground cable all the way to the frame ground point and the positive cable all the way to the starter terminal. Don't overtighten the starter terminal nut! It doesn't take much force to snap the threaded post. Are you in an area where they use road salt?

If you're adventurous, have someone hold the key in start position for a few seconds after the first inadequate engine movement while you feel the positive and ground cables by the battery. Does one feel notably warmer than the other? One warmer cable suggests more resistance in that cable. Watch your hands because the starter might suddenly kick in at full speed while the key is in start position.

Sixto
04 LE FWD 240k miles

Nope. I live in California.

 

While the van is running voltage should be 13.8 - 14.2v.

Fully charged battery is 12.67 volts. 11.8 is considered dead(meaning you’d need to replace all the amps). The Sienna uses a group 24F battery and has probably around 70amp hours capacity… using a tender jr less than 1 amp would take 70 hours(ish) to fully charge..

You can verify woke running if you are getting g the same voltage at the back of the alternator and battery terminals. If difference then I’d check the cable between alt and battery.
If you’re battery is fully charged and then 11.8 or 12.2 ish in the AM then I’d look for a drain..
But you’d need to verify the battery gets fully charged.
Hope some of this might help..

I worked for Interstate Batteries for about 20 years, I have diagnosed probably a thousand electrical problems.

 

While the van is running voltage should be 13.8 - 14.2v.

Fully charged battery is 12.67 volts. 11.8 is considered dead(meaning you’d need to replace all the amps). The Sienna uses a group 24F battery and has probably around 70amp hours capacity… using a tender jr less than 1 amp would take 70 hours(ish) to fully charge..

You can verify woke running if you are getting g the same voltage at the back of the alternator and battery terminals. If difference then I’d check the cable between alt and battery.
If you’re battery is fully charged and then 11.8 or 12.2 ish in the AM then I’d look for a drain..
But you’d need to verify the battery gets fully charged.
Hope some of this might help..

I worked for Interstate Batteries for about 20 years, I have diagnosed probably a thousand electrical problems.

I used beefy battery tender (max 4.5A output) to fully charge the battery. I compared battery level with my other car (2021 Lexus RX350, V6) to see if there is any difference in voltage overnight, but they were equivalent.

Sienna 12.0V @battery, 11.7V w/ODBII (2 years old battery from Costco)​

RX350 12.3V @battery, 11.7V w/OBDII (>4 years old original battery)​

​

Again, because there was no issue clanking the engine after the 2nd attempt, I have to think that battery may not be an issue.

 

I would be inclined to check (with a DMM) the voltage of the battery, independent of the OBD port, to try to get REAL voltage. That said, you ALSO need to load test the battery. It should be as simple as going to a parts store for a charging system and battery test. In theory, the battery should be 12.5+ VDC at the battery, when fully charged, after shutting down the alternator. After sitting overnight (12 hours), it shouldn't have dropped more than 0.1 or 0.2 volts. 12.0 V is a "dead" battery because it should still be 12.5+. The question is, is it dead because the battery is dead, the cables or terminals are faulty, the alternator is weak and/or slipping, or you have a parasitic drain on the system.

If you get the charging system/battery test and it shows the issue, you'll know what the issue is. If it checks out, it almost HAS to be the cables or terminals. Alternately, you can just guess it's a bad battery and replace it. As a slight aside, it's almost certain, in my mind, that the battery is bad. However, you may have a second issue that made the battery prematurely go bad. I'd still get the test, even if I got a new battery.

 

I took the battery to O'Reilly auto parts for battery load test, and it was tested fine.
But then just before I go pick up my son today, it happened. This time was worse.

After starting engine, it suddenly shut off within a second. All lights were off on the dashboard.
Then I turn the ignition key to OFF position and tried to restart. It cranked few times, but suddenly stopped cranking more. All lights remained off.
Again, I turn the ignition key to OFF & ON position several times, but this time no light came back to the dashboard and I wasn't able to crank at all.
I immediately checked battery voltage with DMM and it was 12.57V.

Eventually, engine started after several attempts.

I was lucky to capture this incident on video and here is the link to it.

https://photos.app.goo.gl/f1X9XHdZqhDFEFDQ9

I need to start checking electrical wiring diagram to figure this out (unless someone can tell what's going on...)

 

At this point might be worth it to take it to a shop with a good diagnostic(not a part changer). Pay the fee and see what they suggest. Could save you a lot of headaches. I’m for self evaluation, but chasing down an electrical problem can be a nightmare.
Especially when they might hook up and find a $10 relay is the problem.

Good luck

 

At this point might be worth it to take it to a shop with a good diagnostic(not a part changer). Pay the fee and see what they suggest. Could save you a lot of headaches. I’m for self evaluation, but chasing down an electrical problem can be a nightmare.
Especially when they might hook up and find a $10 relay is the problem.

Good luck

Before going that direction, I will swap starter & A/C relay as suggested by sixto to check.

 

Cable test for voltage drop

 

Could this be just due to dying starter...?
My van just passed 180k.

 

Here is an update.

I swapped starter & A/C relays few days ago, but hesitation at the start up has been increasing its frequency (from once in ~3 weeks to every few days)
And I've seen other threads about starter motor issue around my van's mileage (180k).
So I purchased both starter motor (remanufactured) and relay from dealer and replaced them today.
New starter runs quick and starts engine faster now. Only time can tell, but I hope this is it.