# 2002 Toyota Sienna troubleshooting electrical issue **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** electrical-wiring, toyota\ **Created:** [March 6, 2024, 6:26am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494 "2024-03-06T06:26:11Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 6, 2024, 6:26am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/1 "2024-03-06T06:26:11Z")
Hi, any help is greatly appreciated thank you 🙏🏼🙏🏼🙏🏼🙏🏼 Working on my friend’s 2002 Toyota Sienna V6 with high mileage… She was getting a bunch of squealing and I think power steering went out from time to time… Then her speedometer/ dash, but not the lights went out among with the radio and the van was surging/ not fitting correctly… She got it jumped when it wouldn’t start… Drove it home and it wouldn’t start… Another friend tried replacing the alternator and charging the battery… It started but shut off about 2 minutes later she said I just tested the original alternator and charged the battery at the auto parts store. They seem good battery is less than 6 months old. Yet to start it… Lights come on, radio plays, no codes… I’m a bit at a loss for where to narrow it down to … Ignition/spark? bad crankshaft pulley? Wiring? I don’t think it should quit after 2 minutes with a charged battery… I’m gonna start it tomorrow and check the voltage across the terminal while it’s running, listen for missing, and visually check the belts in motion… Then maybe I’m leaning toward checking the ignition and spark… Could it be the computer or the dreaded gremlin in the electric system… I checked the fuses for continuity, but not the relays… ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 6, 2024, 7:45am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/2 "2024-03-06T07:45:12Z")
I think I found something… Having trouble uploading images but… Seems there might be an issue in engine room 1 fuse box from the diagrams I find on Chilton… I’m gonna check the relays tomorrow… 🙏🏼🤞🏼🙏🏼🤞🏼🙏🏼🤞🏼🙏🏼🤞🏼🙏🏼 ---
**Author:** ![PvtPublic](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/pvtpublic/32/13089_2.png) [@PvtPublic](https://community.cartalk.com/u/PvtPublic)\ **Post date:** [March 6, 2024, 8:08am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/3 "2024-03-06T08:08:09Z")
Or it could be the usual Toyota and it needs to “relearn” idle and a couple other parameters after totally losing power. Start it and use the throttle to keep it running, or drive it for 15 minutes or so. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [March 6, 2024, 12:16pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/4 "2024-03-06T12:16:54Z")
Measure the voltage before and after starting the engine. Post those 2 values and THEN we’ll figure the next step. Without data, it is just guessing. ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [March 6, 2024, 1:47pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/5 "2024-03-06T13:47:31Z")
Is the serpentine belt loose? That will cause squealing and might lead to power steering loss if the belt is too loose to spin the power steering pump. It’s a cheap place to start if all that’s needed is to take the slack out of the belt. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [March 6, 2024, 10:07pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/6 "2024-03-06T22:07:21Z")
> [@jtsanders](#): > > Is the serpentine belt loose? +1. That’s the first thing I would check for these sort of symptoms. If such a thing can be done safely, temporarily remove the belt, start & idle the engine briefly, to see if the squealing goes away for example. Also some sort of pcm memory minder should be used to maintain the data in the pcm memory during battery replacement . Otherwise all the helpful diagnostic codes get lost as well as the engine’s learned parameters. . ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 6, 2024, 10:35pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/7 "2024-03-06T22:35:51Z")
Pretty sure belt was loose. Doesn’t have a serpentine belt… Just two accessory belts coming off the engine. The one farthest left from the crankshaft drives the alternator… Relays seem good… Lot of the problems seem to be coming from one fuse box… I’m gonna reassemble and do more tests and check back in… ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 6, 2024, 10:36pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/8 "2024-03-06T22:36:57Z")
Even with no alternator the car ought to run for more than 2 minutes, right? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [March 6, 2024, 10:41pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/9 "2024-03-06T22:41:32Z")
> [@danielscottclark](#): > > Even with no alternator the car ought to run for more than 2 minutes, right? Yes at least on my cars, if battery fully charged and no unusual electric demands, stereos & headlights off. When it doesn’t start, what exactly happens? Do you hear the normal “rrr rrr rrr” sound w/key in “start”, but it never catches and run? Battery voltage measurements both with engine off and idling would be helpful. Any indication rain water getting into the engine compartment and oxidizing the electrical connectors? Checking for visible spark at a spark plug makes sense when it cranks but won’t start. ---
**Author:** ![Rainflurry](https://avatars.discourse-cdn.com/v4/letter/r/cab0a1/32.png) [@Rainflurry](https://community.cartalk.com/u/Rainflurry)\ **Post date:** [March 6, 2024, 11:21pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/10 "2024-03-06T23:21:26Z")
> [@Mustangman](#): > > Measure the voltage before and after starting the engine. Even if they come back at 12.6V and 14.5V, you still have no idea if the alternator is working properly. The OP needs to measure the alternator current output as well. ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 6, 2024, 11:51pm UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/11 "2024-03-06T23:51:00Z")
Installed alternator. Not sure how tight the belt needs be… It’s fairly tight… Doesn’t bounce, barely moves… 11.5 - 12 at battery when off Just a little drop when running Current at alternator positive poll to case is 11.5 when running Guess I gotta replace the alternator… ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 7, 2024, 12:13am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/12 "2024-03-07T00:13:01Z")
Should the alternator be hot/powered with the vehicle off? Just sparked when taking off… oops… ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [March 7, 2024, 12:15am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/13 "2024-03-07T00:15:39Z")
Disconnect the negative battery cable. Tester ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 7, 2024, 12:16am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/14 "2024-03-07T00:16:20Z")
Maybe it’s the diode/voltage regulator? Would that explain why it bench tests… ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 7, 2024, 12:17am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/15 "2024-03-07T00:17:57Z")
I took off the positive for now… ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 7, 2024, 12:30am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/16 "2024-03-07T00:30:56Z")
Diode seems to test okay ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [March 7, 2024, 12:40am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/17 "2024-03-07T00:40:21Z")
> [@danielscottclark](#): > > I took off the positive for now… [![](https://global.discourse-cdn.com/cartalk/original/3X/0/9/09d5931189dceed9b0c553c40cbc1cc200af7704.jpeg "Why we should disconnect battery negative first?") ](https://www.youtube.com/watch?v=SHRPLmito7M) Tester ---
**Author:** ![danielscottclark](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@danielscottclark](https://community.cartalk.com/u/danielscottclark)\ **Post date:** [March 7, 2024, 1:31am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/18 "2024-03-07T01:31:39Z")
I’m thinking the ECU now 🙏🏼🙏🏼🙏🏼🙏🏼 ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [March 7, 2024, 1:40am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/19 "2024-03-07T01:40:46Z")
Did you check all the fuses, big and small?? ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [March 7, 2024, 3:01am UTC](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494/20 "2024-03-07T03:01:58Z")
> [@Rainflurry](#): > > The OP needs to measure the alternator current output as well. You have made the assumption that I’d make a conclusion based on that data. Fact is, the running voltage showed the alternator was not working. > [@danielscottclark](#): > > Current at alternator positive poll to case is 11.5 when running So no power from the alternator. > [@danielscottclark](#): > > Should the alternator be hot/powered with the vehicle off Yes, because it is hooked the the battery to charge it. Find the field wire connection on the back of the alternator. Restart the engine. Is there battery voltage at the field wire connection? Yes? The alternator is bad. No? Trace the connection back to the ECU using an actual wire diagram for the charging system. Anything in that circuit could be the problem including the ECU. [Next page](https://community.cartalk.com/t/2002-toyota-sienna-troubleshooting-electrical-issue/194494.md?page=2)