REX engine sometimes starts at 30-35% battery instead of 6%

Hi i3 owners,

I am a Colorado resident. I recently bought a used 2014 i3 from out of state and noticed that REX engine sometimes starts too early, usually between 30-35% battery charge. The REX is set to start at 6% battery charge by factory. When this happens, I usually continue driving. The way to reset it is I need to press the car START button off and back on. Then the REX gets set to 6% again. The dealer is telling me that they cannot diagnose this problem nor they can see any errors in the computer log. They replaced several parts including REX computer, but none fixed the problem. The battery is at about 75% capacity when fully charged. Not quite ready for warranty replacement but its getting close.

Has anyone else experienced this issue? If so, how was it resolved?

Many thanks, I love my i3 but this is a bothersome problem and I'd like to have it fixed.

Any way to contact the original owner? Maybe the dealer could contact the owner and have him call you?
Almost sounds like the car was coded at some point but the dealer should be able to recognize this. Perhaps if the dealer re-loaded the most recent software it would fix the issue ?
What are the conditions, etc when the car charges to 75%? DC Fast Charge? AC charge at home (what voltage)? L2 charge in a public lot?

Dealer did re-program the REX feature before I got it, enabling 'charge-now' option, but my service wiped it out by accident and after it happened again the Service restored factory USA setting. Then it happened again. I only charge the car at home with factory L1 charger at 110VAC. Service did fast charge the car several times, but why would that matter? I do have a dongle to re-program the car and I am tempted to do it, enable all EU features, REX overwrite and larger fuel capacity.

thanks for the reply

If DC fast charging works (charges to 100%) and the supplied L1 charger only charges to 75%, that may be a clue as to what's happening.
Sometimes the connection may be marginal inside your outlet which causes charging to stop. I've seen pics of burned outlets while using the L1 charger. There is a menu item where you can set the charge speed (or current?). As a test, you might want to set that to the lowest setting and see if it charges to 100%
Also you might try a different outlet, preferably on a different circuit. I've tripped the breaker a couple of times while charging because I over loaded the circuit. I assume that's not the case for you because a tripped breaker is obvious.
Also sometimes the locking pin sometimes malfunctions on the L1 which would cause it to stop charging
Or...the supplied charger may be defective. Anyway to try a different one?

Regarding the REx coming on at 30-35%, I'm at a loss for options. I like your idea of coding to EU parameters and see what happens.

The OUC's output is quite low, relatively speaking, and it could take nearly 20-hours to recharge a nearly depleted battery. How low was the battery, and how long was it plugged in?

If it consistently can't be recharged higher than 75%, something's wrong, either with the OUC, or the car.

When plugged in, does the car say it's fully charged, or if not, is the charging time indicating some time in the future?

Have you tried some other L1 or L2 EVSE?

I interpreted i3co's comment to imply that the maximum capacity of his i3's battery pack is 75% of its new capacity, not that charging increases the indicated charge level to only 75%. If my understanding is correct, maybe a bad cell results in his battery pack's voltage dropping to that when the REx engine should start, 6% of the full capacity, even though the battery management system thinks the charge level is 30-35%.

This behavior could also be explained by the charge levels among cells being very different such that the voltages of those cells at the lowest charge levels drop to the level where the battery management system prevents further discharge and starts the REx engine.

Both a bad cell and very unbalanced cell charge levels could explain the loss of 25% of the pack's usable capacity.

These are wild-assed guesses on my part. I don't think we know exactly how a REx behaves with a bad cell or badly unbalanced cells.

alohart, you are correct in interpreting my first post. What you said makes sense, I am EE by profession and a bad cell or a bad connection between the cells could cause this erratic REx behavior. Again it happened last night when driving the car from Service, battery was at 26% charge with 20 electric miles left. REx ran for about 4-5 miles and then turned itself off. I didn't have to stop / start engine. Makes me think that a single battery cell is playing tricks on me. But the dealer would not touch it since its still under warranty.

thanks, i3co