Jenson Button is remaining upbeat about McLaren's prospects in 2015 despite only managing six laps on day two of the first pre-season test in Jerez.
The 2009 world champion suffered reliability problems which hampered his chances of setting a meaningful time, but the Briton is hoping for an improvement in fortune on the final two days of the test.
Button told reporters: "It has not been the easiest start to the season but it is a very complicated power unit.
"We understand the issue and we have our heads around it - that's what the last run in the wet was about - so we are hoping for a much more productive day three and day four."
McLaren finished fifth in the 2014 constructors' championship.
