Powertrain, generic · Fuel and air metering (injector circuit)

P0234 Turbocharger/Supercharger A Overboost Condition

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0234 is a function code, not a sensor fault: the engine module compares target and actual boost, and actual boost stays above target although the control is already lowering it (wastegate opened, variable vanes opened). GM petrol engines set it at 20–35 kPa over target with the warning light in the first trip; GM diesels with variable vanes at 7–10 kPa, after two trips; Ford EcoBoost at about 28 kPa (4 psi) over 5 s while the wastegate is already commanded fully open. Ford diesels instead use P0234 for exhaust back pressure above 4.0–4.5 bar. The engine limits boost or enters limp mode. Typical causes are a wastegate stuck closed, sooted variable vanes or a faulty control valve; Audi traced cases on the Q7 TDI to cracked exhaust parts jamming the turbo vanes. Check the boost sensor against barometric pressure first.

Likely causes

Wastegate stuck closed, actuator or linkage sticking, control hose off or blocked
Variable turbine vanes sooted or stuck closed (diesel)
Boost control valve or electric actuator faulty
Boost or manifold sensor reading too high (drift)
Software or calibration, tuning

Symptoms

  • Check engine light on
  • Limp mode with clear loss of power
  • Boost overshoots on acceleration, then power drops
  • Knocking under full load (petrol) or smoke (diesel)

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–2,500
Time1–6 h

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

What to check first

  1. Check actuator movement
  2. Inspect vacuum lines
  3. Compare desired and actual boost

Parts involved

turbochargerwastegatevariable geometry vanesboost control valve

Related codes

P0299P2263P0236P0243P0045P259F

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.