2002 Opel Zafira, 2.0 diesel motor. Loss of power at times and dash light c?

2002 Opel Zafira, 2.0 diesel engine. Loss of power at times and dash light comes on. light is auto with wrench through it. when light goes off power returns to engine. Is this an issue with the turbo? Just performed complete service on car replacing all filters and oil, reset all maint and codes. Problem was occurring before and after service .