Tickford Racing is frantically checking over Jake Kostecki's car after consecutive practice dramas.
Kostecki triggered a red flag in Practice 2 at Symmons Plains after he ground to a halt on the back straight.
The session was topped by Shane van Gisbergen, who pipped Andre Heimgartner by just 0.02s.
A suspected loose wire inside the lambda plug triggered the electrics issue on the #56.
The piece provides the ECU (engine control unit) with an electric signal to control the air-fuel ratio.
It came after the TRADIE Mustang suffered suspected shift-cut issues in the morning session.
Race engineer on the #56, Rhys Lenegan, told Supercars.com the car will be ready for three-part ARMOR ALL Qualifying.
Lenegan also added the two issues were separate; the team was also forced to repair a broken air hose on Kostecki's helmet.
Kostecki's second race in Sydney was also affected by a starter motor issue.
Cam Waters was the highest placed driver in Practice 2 in 14th, ahead of James Courtney (15th) and Thomas Randle (21st).
Kostecki only completed five laps in the session and wound up 25th and last.
Cars will return for qualifying at 1:50pm AEDT. CLICK HERE to purchase your tickets.
Every session of the event will be broadcast live on Fox Sports 506 and streamed on Kayo.
The Seven Network will broadcast highlights on Saturday and Sunday.