what does it mean when red warning light stays on at engine start up?

What is your question?

2001 vaden plas xj8. Red warning light stays on after system check is complete. Today is first time it has happened. Checked manual but no good explanation. Simply says it will affect drivability. Had thermostat and transmission replaced with last 2 months. No visible leaks or strange noises.

What makes this problem better or worse?

Don’t know

How long has your 2001 Jaguar Vanden Plas had this problem?

First time