Powertrain, generic (extended)

P259B Turbocharger Boost Control Position Sensor B Performance - Stuck High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P259B is logged when the boost control actuator watched by position sensor B is found stuck at the high end of its travel, or fails to return to its rest position, while the sensor signal itself is plausible. A sensor B exists mainly on twin-turbo or two-stage engines. No manufacturer publishes P259B. On the A side, GM checks that the vanes spring back to fully open after the actuator is released and sets P2599 if they stay above 15 % (vacuum) or 5 % (electric); a comparable test for B is likely but not documented. GM bulletin PI1260 shows how vacuum leaks upset such pneumatic actuators. CARB 13 CCR 1968.2 asks for boost control faults to be caught in both directions, including boost above the commanded level. P259A is the low-side partner. The engine may cut power to avoid overboost.

Likely causes

Mechanism of charger B seized toward the closed or high position
Return spring or linkage of actuator B binding
Vacuum solenoid or hose of actuator B faulty (pneumatic systems)

Symptoms

  • Engine warning lamp on
  • Power cut-out under full load to prevent overboost

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–2,500
Time0.5–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

turbo actuator position sensor bturbo actuator b

Related codes

P259AP2599P2587P2586

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.