Instructions for use of Rex

[sdi]

Hi. I have had my i3 94ah Rex for a few months. The car has been great, I'm really happy with it.

I had my first negative experience with it last week. It seem I was missing some knowledge on how the Rex should be used which left me stranded for a few hours.

We were doing a long drive after a weekend break, and I knew I would need the Rex to finish off the journey. It was a fairly cold day and we had the fan on low to keep the glass clear of mist. No other lights or aux kit on. At around 5% the Rex kicked in. We were just pulling off the motorway, so going speeds around 50-60mph with roundabouts, nothing too strenuous. We slowly watched the electric range drop from about 5 miles to 3 miles - it seemed like the Rex wasn't keeping up. At about 2 miles of battery remaining we got a drive train error and engine warning light and the Rex stopped altogether (the fuel gauge went grey again).

At that point we pulled over to safety and called BMW to recover us since I suspected the Rex had malfunctioned. After 3 hours of waiting a low loader arrived to take my car to the dealer, and a taxi for me.

After diagnostic, they reported that no fault was found, and I was liable to 3 hours of workshop labour. Apparently I had not used the Rex correctly and it was my fault. Obviously I made a bit of noise and luckily got this waived by BMW UK - they put it down to poor handover. I should have started the Rex manually much earlier.

I did a bit more home work. Reading the in-car and online manual, I couldn't see any reference to driving style while using the Rex, just a warning that you might get reduced output in some conditions.

I made contact with the dealer again and had a really good chat with the senior tech. He gave the impression that all was not quite right in how BMW have been handling this, but couldn't say as much, just that leaving the Rex to default behaviour will probably cause problems. Maybe the class action law suit in the US is meaning they are keeping their powder dry for a bit.

It seems they should either adjust the software to bring on the Rex earlier in certain conditions, or at least document properly in the operator manual how it should be used.

Has anyone else had a similar experience?

 

[epirali]

Obviously there is nothing you are supposed to do for the REX to work, except having gas. And the drive error is not from user behavior. The only thing I have noticed with the REX is that if it is cold outside when the engine first starts it can not run at full power and the battery level does drop for a while. This is nerve racking. I usually slow way down until REX warms up and then it will catch back up. But it does not fault or shut off. I can see that if the REX came on when car was under heavy load (going uphill, headwind, speed) then you could potentially drain the battery before engine warmed up.

All of this would be mitigated in the US by not disabling the hold SOC function. Then you could turn on REX at higher SOC when you know you will need it. Yes you can code the car, but the unhacked use case is crippled. But if your car doesn't enable SOC hold consider enabling it via coding.

But definitely make sure they explain the error.

 

[brorob]

Sounds to me like they were trying to place blame for a malfunction on you. I'd be curious what they meant when they stated that you didn't use it correctly. Here in the U.S. We don't have the option to turn it on manually, unless the car is coded. I've had my REx for about a year and a half and never had a problem with the REx coming on and keeping the batteries charged at a level where the vehicle operated normally. I did experience a warning once that power reduction was possible, but it was cold out, headlights, heater, seat heater, and HK stereo was on, and I was driving about 55 mph. I turned off a few accessories for a few minutes and then everything returned to normal.

The system is setup to be fully automatic so unless you did something like put diesel fuel in the gas tank or didn't have sufficient gas in the tank, don't know how you can use the REx incorrectly. Unless the car is setup different in the UK where you're supposed to turn it on early manually, but that doesn't seem right. Sounds like they were just trying to place blame on you.

The errors you received seem related to the problem. There have been posts about those errors, I thought a few posts related this to a low charge or fault in the 12V battery.

 

[MikeS]

sdi - I assume you are in uk - I frequently leave my soc to run down until the REX cuts in automatically and have never has a problem. The only thing you need to watch is that it takes the REX a little while to warm up until it produces full power. When the rex is at full power it will maintain the soc as long as you don't exceed 70 mph on the flat. If you exceed this it cant keep up and similarly until its warmed up it wont maintain the soc.

 

[gururise]

I've never had a problem with my REX coming on automatically at 6.5% SOC. I live in So Cal, and we don't have extreme cold weather here. REX just powers on and I can drive until I run out of gas.

 

[alohart]

There have been several reports in the U.S. in which the power bars in the power meter gradually began graying out with power dropping until the car would no longer move even though the reported charge level was greater than 0% and as high as ~6%. This has occurred with both BEV's and REx's. With the REx's, the REx engine started but did not run fast enough to provide sufficient power for propulsion. This problem is apparently caused by the miscalculation of the battery pack's charge level, maybe as a result of a bug in a recent software update.

In a REx, the car thinks the charge level is higher than it really is so the REx engine doesn't run as fast as it would if the car thought the battery pack's charge level were lower. As the charge level continues dropping, the voltage of the battery pack, one of its modules, or maybe one of the battery cells drops below the level that is deemed the lowest voltage at which no cell damage could occur, so the car decreases the available power to protect the battery pack until no power is available. In a BEV, the car just stops even though the displayed charge level is >0%. Some have surmised that this problem might be more likely to occur with 2014 models, but I think it's too early to know for sure.

Apparently, BMW has a software patch that they think might fix this problem until a new software update can be released. For this patch to be installed, a dealer must connect the car directly to BMW headquarters to establish an IRAP session.

Hopefully, your BMW dealer can ask BMW engineers about a bug in calculating the battery pack's charge level that could be the cause of the problem that you had,

 

[sdi]

Thanks for your responses. Yes I'm in the UK and the hold SOC is available in the menu without a patch. I tried it on my 25mi journey home from work last week and it maintained 74.5% for the entire journey with headlights, radio, low fan on, so seemed ok that time.

It is reassuring that you agree something 'went wrong' on that day. The senior tech did think there could have been some software error/bug which caused the strange behaviour, but I don't think anything has been patched on my car.

I thought I'd read somewhere that the Rex has a separate diagnostic connector to the main car. He disagreed with this and I can no longer find the reference.

Unfortunately it's kind of my word against theirs now. He says no fault found and BMW UK say it was operator error. I would always Hold SOC early in future.

That day was quite cold, there were two of us in the car and possibly the equivalent of a third person in luggage etc in the back so possibly the odds were stacked against the Rex, but I'd like to know why it shut off when we were at around 3% SOC and never came back on. Surely that would feature in the diagnostic?

 

[alohart]

I'd like to know why it shut off when we were at around 3% SOC and never came back on. Surely that would feature in the diagnostic?

That's not normal but maybe this behavior doesn't set a diagnostic trouble code (DTC) because it was not expected when the system was designed. But you can be certain that operator error was not the cause, so the fact that the dealer accused you of such indicates that the dealer really doesn't understand how the REx works or doesn't want to deal with the problem. Because of some similar issues on this side of the pond, maybe a software update will fix the problem eventually.

 

[gururise]

Apparently there is discussion in the Facebook group about the latest SOM software update causing a miscalculation to occur at low SOC that could prevent the REX from turning on when it should. Apparently BMW has just become aware of this bug and they issued a patch which requires an IRAP session. This is such a new problem, many dealers are currently unaware. They are working on a software update that will not require a lengthy IRAP session and can be applied at your next maintenance.

I would imagine by the time you get the letter about the fuel line recall, the software update will be ready and would be applied at the same time.

 

[sdi]

This is great info. Thanks.

 

[Hatvany]

My 2015 Rex has just been picked up by BMW and taken into the Dealer. The car tried to perform a maintenance run on the Rex yesterday, as the Rex had not been used for a couple of months. Error messages came up saying HOLD STATE OF CHARGE FUNCTION NOT AVAILABLE, the DRIVETRAIN symbol on the screen lit up and I also got a message DRIVE IMMEDIATELY TO DEALER. I tried manually selecting HOLD STATE OF CHARGE when the car was showing 52% charged but again the warning messages. I'll post again when the trouble has been diagnosed.