How to avoid the most common SUA – waiting for green light in a traffic stop

December 28th, 2015 No Comments   Posted in sudden unintended acceleration

How to avoid the most common SUA – waiting for green light in a traffic stop

Wishing you Merry Christmas and Happy New Year.

After reading all the technical papers on SUA, it appears that the most common SUA is during a stop waiting for the traffic light to change from red to green.

The habit of idling in gear (drive) with your foot on the brake to prevent the vehicle from moving forward causes a drop in engine RPM (additional mechanical load for idling in gear), drop in voltage (additional electrical load by brake lights), and further drop in engine power (air-con compressor cuts in).

As the voltage drops due to lower engines power and speed, the idling controller is commanded by the computer box to raise RPM to recharge the battery.

And if the alternator is under-sized, or the battery is unable to store the charge because it is old or faulty, then the computer will keep on demanding a higher RPM, and ultimately results in an SUA, unless the driver immediately shifts to neutral gear or turns off the engine. So the best protection against SUA – once you stop in a traffic light, shift immediately to neutral and avoid stepping on the foot brake by engaging the hand brake.

Better, turn off air-con compressor and just engage fan only to avoid additional mechanical and electrical loads that will cause the engine RPM to drop and avoid losing battery charge and need for computer to raise engine RPM leading to an SUA event.

Also, after a night’s driving in heavy traffic, always idle the SUV for 3-5 minutes to normalize engine performance and turn-off engine at idle speed so the computer memorizes this last setting (never turn-off while revving up).

The following morning, always start in park (P) and idle for 3-5 minutes to observe engine performance, with the engine stabilized at low idle (not high idle when you turn on engine for the first time), before you drive off in reverse or drive.

Have an SUA-free holiday to all.