PCV system failure in your 2018 GMC Terrain causes various driveability symptoms and can lead to oil leaks, consumption issues, and check engine lights. The positive crankcase ventilation system maintains proper engine breathing, and its failure creates multiple problems.
PCV System Function
The PCV system routes crankcase gases—blow-by from combustion—back into the intake to be burned rather than venting to atmosphere. The PCV valve regulates this flow based on engine vacuum, maintaining proper crankcase pressure.
Terrain PCV Design
The 2018 Terrain's turbo engines (1.5L and 2.0L) have integrated PCV systems that handle higher blow-by pressures from turbocharged operation. Failure creates more pronounced symptoms than naturally aspirated engines.
Failure Symptoms
A stuck-open PCV creates a large vacuum leak causing rough idle, lean codes (P0171), and possible stalling. A stuck-closed PCV causes crankcase pressure buildup, pushing oil past seals and dipstick, increasing oil consumption, and possibly popping the dipstick out.
Oil in Intake
Failed PCV systems can allow excessive oil vapor into the intake, contaminating the MAF sensor, fouling throttle body, and causing carbon buildup. On turbo engines, oil can contaminate the intercooler.