What Does P004B Mean?
The PCM has determined that the turbocharger/supercharger boost control 'B' circuit is operating outside its expected performance range. The secondary boost control solenoid is functioning electrically but the resulting boost pressure from the 'B' system does not match commanded levels within acceptable tolerances. The driver may notice inconsistent power, surging, or reduced performance during transitions between boost stages.
Common Causes
30%
Sticking or binding secondary wastegate actuator or VGT mechanism
25%
Boost or vacuum leak in the secondary turbo system plumbing
20%
Degraded boost control solenoid 'B' with weak or inconsistent output
15%
Faulty boost pressure sensor or secondary turbo speed sensor providing incorrect feedback
10%
Carbon buildup on the secondary wastegate or VGT vanes restricting proper movement
Diagnostic Steps
1
Monitor live data comparing commanded vs. actual boost pressure, paying special attention to transitions between low-boost and high-boost modes where the 'B' solenoid becomes active.
2
Perform a boost leak test on the entire intake tract to identify leaks in the secondary turbo plumbing, intercooler, or interconnecting piping.
3
Inspect the secondary wastegate or VGT actuator for free movement — manually actuate it (engine off, cooled down) and check for binding, stiffness, or limited range of motion.
4
Command the solenoid 'B' on and off using a bi-directional scan tool while monitoring secondary boost response — a sluggish or absent response indicates a mechanical issue with the actuator.
5
On VGT turbos, inspect the variable geometry vanes for carbon buildup or soot contamination, which is a common cause of restricted movement on diesel applications.
Estimated Repair Cost
$250 - $1,200
Parts + labor, varies by vehicle and location
The PCM has determined that the turbocharger/supercharger boost control 'B' circuit is operating outside its expected performance range. The secondary boost control solenoid is functioning electrically but the resulting boost pressure from the 'B' system does not match commanded levels within accept...
The most common cause of P004B (Turbocharger/Supercharger Boost Control "B" Circuit Range/Performance) is: Sticking or binding secondary wastegate actuator or VGT mechanism
Typical repair costs for P004B range from $250 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe for limited driving at moderate speeds. Avoid heavy acceleration or towing. The vehicle may exhibit unpredictable power delivery during boost transitions. If boost is exceeding target, there is a risk of engine damage — stop driving and have the vehicle inspected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P004B to identify the root cause.
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Quick Info
Category
Powertrain
System
Forced Induction / Turbocharger
Difficulty
Type
Generic (SAE)
Recommended Tools
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