Computers as such do not respond well to changes in voltage. There's a lot of drain on the Smart electric system. The Bosch alternator is rated at 90 amps and I don't see how it keeps from robbing a lot of our 70 hp from the engine. But when you start your Smart and put it in gear it has to run a motor to depress the clutch, run another motor to engage it in first gear or reverse. Besides that your fuel pump is running so it's drawing amperage. The coil packs are drawing power. You have a electric vacuum pump that provides constant vacuum for the Smart's power brakes. You've more than likely got on the heater or the A/C so the blower motor is running and the motors on the dampener doors are active.
A big draw on the electrical system in the Smart is the heated seats if you have them. All the systems like ABS, Stability control and hill star assist are all active. If it's nighttime your lights are on, maybe the radio too. So you see there are a lot of constantly changing drains on the electric system. If you are idling at a stoplight and the system is drawing more power than the alternator is putting out at a given RPM then it is going to draw from the battery. So with all these events going on electrically behind the scenes voltage can vary especially if by happen chance 2 or 3 things cycles occasionally at the same time you are going to get a drop in voltage albeit milliseconds, but if the computer is operating and the voltage goes south even for milliseconds it is easy for it to glitch and "drop the ball". Since the main draw when driving is the clutch actuator and the double gear change motors when you pop it in gear you have instantly dropped the voltage because they both begin actuating at the same time to get you moving.
Every time it shifts gears there is this coordination between the transmission control module and the engine control module for the smart to successfully execute a gear change that we all complain is too slow. At a gear change it lets off the gas disengages the clutch shifts the gear, re-engages the clutch and presses the gas pedal back to the same place it was in the matter of a second. So if that is going on and say the air conditioner compressor cycles or the intermittent wipers takes a swipe or the heated seat kicks on, you can see voltage fluctuate and hence it is possible to get a glitch and gears go south.
I put a full time digital voltage gauge on Max and in normal operation driving down the road it normally reads 14.2 volts and fluctuates down to 13.8. or 13.9. Kicking on a heated seat will cause it to drop clear down in the 12.7 volt range for a second then the alternator will kick in and stabilize the voltage back to 13.8 to 14.2 range again.
In defense of the alternator Bosch did an outstanding job with keeping the voltage steady and it puts out a lot of amps even at idle. I can idle with the headlights on and I have a mountain of LED's throughout my Smart, also run the A/C and the radio and at idle it still maintains 14.2 volts.
So you can see how a dirty battery terminal or a rusty ground strap can wreak havoc on the voltage staying steady enough to keep the computer operating in spec. I run most of the time in manual mode because I have found that letting it auto shift, if I take off easy as in making a left hand turn it will shift to 2nd and then as I get straightened out on the road and push the gas pedal down the computer decides to shift on up to 3rd gear and lug the engine down to that famous drone sound. And there have been a couple of times it was shifting as I tromped it to pull out and it panicked and wouldn't shift into any gear for a second or two, but it seems like an eternity. DCO
