Warning light on dash and hard to start.

Experienced the issue with owner present.

Interrogated the owner as to previous work.

The vehicle had a service a while back and then issues appeared. First the owner was told to make sure he uses 98 fuel.
On second visit to his service provider he was advised that the oxygen sensors needed replacing, this was carried out and the warning light came back with same cranking issues. The third attempt was to replace the battery.