Code 31, Turbo OVERBOOST - 4.3L Turbo
On turbocharged engines, exhaust gases pass from exhaust manifold through turbocharger, turning turbine blades. Compressor side of turbocharger also turns, pulling air through air filter and pushing it into intake manifold under pressure.
Wastegate is normally closed, but will open to by-pass exhaust gases when an overboost condition exists. This is determined through monitored MAP sensor signals. Under normal driving conditions, ECM energizes wastegate control (solenoid) valve. This blocks off intake manifold pressure from wastegate actuator diaphragm. When overboost condition exists, ECM will de-energize wastegate control (solenoid) valve, allowing intake manifold pressure to act upon actuator diaphragm, opening wastegate.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Code 31 will set when Code 33 is not set and excessive manifold boost pressure is sensed for 2 seconds. This step tests ability of actuator to open wastegate. Code 31 may be caused by circuit No. 471 shorted to ground, a sticking wastegate or actuator, control (solenoid) valve stuck in closed position, a cut or pinched hose, or a faulty ECM.
- After pressure is applied to valve and then removed, actuator should slowly close wastegate. If not, vent in control (solenoid) valve could be plugged.
- With ignition on and ALDL test terminal "B" grounded, control (solenoid) valve should be energized. This closes off manifold to wastegate actuator.
- This checks electrical control portion of system. With ignition on and engine not running, solenoid should not be energized.