It means the Devils must win by seven or more points in tonight’s final away fixture at Rye House to take all four match points and finish above Ipswich to reach the top six in the table.
Ryan Fisher top-scored for the Devils in their match at Scunthorpe with 13 points, which included a six-point win on a tactical ride in heat 11.
The meeting began promisingly for Plymouth, who took an eight-point lead after four heats, but Scunthorpe came back strongly with six successive 5-1 heat advantages during the middle of the meeting.
Scunthorpe: Rider replacement for Zdenek Holub, Andre Compton 8+1 (4 rides), David Bellego 5+2 (4), Carl Wilkinson 13+1 (6), Leigh Lanham 11+1 (6). Reserves: Alex Davies 7+2 (5), Nike Lunna 9+1 (5).
Plymouth: Ryan Fisher 13 (5), Morten Risager 7+1 (5), Jack Holder 8+1 (6), rider replacement for Todd Kurtz, Kyle Newman 4 (4). Reserves: Sam Simota 5+2 (5), Linus Eklof 3+1 (5)