A scanner would be nice (bg). That car will have actual values and maybe some activation available through a scanner.
But, As I replied I think it can be checked for fault codes by the impulse counting method. There have been many posts on making impulse testers. If you have a scope or voltmeter it can be done using the technique I describe in the DIY article "Evaluating engine controls".
Bosch Master, ASE Master, L1
33 years MB technician