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2011 Sienna 2GR-FE question applicable to all Toyota/Lexus 2GR models I believe.
I have replaced the alternator several times, only to have the alternator fail again within a few weeks. I’ve tried both Denso Reman and good used low mile OEM units. All units bench tested good pre install. New or charged battery each time. When first installed, we are seeing 14v at the battery, Within a day this degrades to 13v and eventually fails to charge after burning out the diode(s) The alternator is getting hot, and actually burns the label off the case when it eventually fails. On acceleration, whining noise is heard that gets progressively worse until the alternator fails. After driving, the alternator had an electrical burning odor.
No blown fuses. No codes (Either OEM or OBD2). All electrical components function perfectly. Zero performance or drivability concerns with the car whatsoever.
I believe we have a severe electrical short somewhere in the system or an ECU failure and I’m wondering if anyone has experienced this with Sienna vans or 2GR Toyotas before? The car is 100% bone stock not even an aftermarket stereo. No alarm system, no tow hitch wiring etc. Zero aftermarket wiring. Car has known history since day one no no floods or other weirdness. Checked engine grounds as clean and making good contact. Checked all connections at battery, ecu, alternaror, as well as unwrapping most of the alternator harness to check for rubbing/shorted wires. West coast car with no corrosion anywhere.
A friend with a 2012 Sienna XLE had the same issue a few years back, we swapped alternators a few times but he eventually gave up and traded it in with 90k miles due to no one being able to figure it out. So I’m thinking this is platform specific.
At this point I’m thinking we may be looking at a bad ECM assuming powers and grounds are good or engine wiring harness. Any ideas for next steps? I guess I’m a little lost when a ECM controlled alternator is compensating for a short/issue with a module or wiring on the network VS the ECM actually putting out bad data to the alternator due to an ECM failure.
Finally, should this be beyond my abilities, is anyone aware of a west coast shop/tech that can diagnose a complex issue like this?
My understanding of this charging system is that it is NOT ECM controlled. At the alternator connector, there's two fused B+ feeds, one light control and one wire that goes to the ECM (labeled the 'M' circuit). I believe the M circuit is a monitor only and does not actually influence alternator operation.
With the alternator getting hot, I'd assume that the alternator is full fielding in response to an electrical load on the system. Do you have an amp clamp, or can you get one? Measuring alternator output current with a working alternator would be a great first step. Something like this would be perfect:
It'd also be good to voltage drop across the B+ and ground circuits while the alternator is charging. From B+ to the alternator stud, and from B- to the alternator case. Both should have less than .5V.
