Have you flushed the fluid in the unit in the car?

 

Flushed, but not addressed the slave yet. Following the Louie Ott/John Veninger PDF. I guess that is next.

 

And pull and clean the lateral acceleration sensor. I had some issues with mine after a good flush and fill and once the sensor was given a liberal "rinse" with DeOxit, been fine since. So, like 30,000 miles or so...Due again this spring.

 

I saw the thread where you suggest removing the transverse lock sensor and shaking it to detect whether the pendulum inside is moving. This is where I am going next. Then on to the lateral acceleration sensor

 

As Rob advised me, the yaw sensor under the driver's seat on my '90 needed cleaning. Simple flushing would not do it as it had metal filings of unknown origin between the magnet and pendulum. I had to push some blue card stock through several times to remove the filings.

Yawsensorbeingcleaned_zpse8cc7b0d.jpg

 

I pulled the transverse lock sensor pictured above and poked inside. The pendulum moves freely.

 

Are ALL the connections clean?

 

All the connections were clean.

 

Replaced the PSD unit with a a spare unit I had on the shelf, flushed the PSD and no more Differential Controller Error.

Turns out the pressure switch was on its way out. It gave it up finally and that led me to swap in a known good unit.