Primastar automatic transmission shifting issues

Whoa, sounds like a proper headache! When you say 'implausible shifting', can you be more specific? Is it slipping, harsh changes, or something else? Has the transmission fluid ever been changed? Low voltage can mess with the electronic controls, but let's rule out the simple stuff first. Hydraulic fluid level okay?

The shifting is erratic, with delays and harsh engagement. The transmission fluid history is unknown. Could undervoltage really cause this, mimicking bad hydraulic fluid?

Okay, erratic shifting and unknown fluid history? That points towards needing a transmission flush, or at least an oil replacement. However, low voltage can absolutely cause havoc with modern automatic gearboxes, as they're heavily reliant on sensors and solenoids. Given the symptoms, and especially the emergency mode, it's best to get it properly diagnosed by a workshop before you start throwing parts at it. Could save you a lot of money in the long run!

I sought professional diagnosis. Undervoltage was the problem, needing electrical repairs and a transmission fluid change. Total repair cost was 240€.