What Does P004C Mean?
The PCM has detected that the turbocharger/supercharger boost control 'B' circuit voltage or signal is lower than expected. This points to a short to ground condition in the secondary boost control solenoid circuit. The driver will experience reduced turbo boost from the secondary system and possible limp mode activation.
Common Causes
35%
Short to ground in the boost solenoid 'B' wiring harness
30%
Internally shorted boost control solenoid 'B' coil
20%
Water intrusion or corrosion in the solenoid 'B' connector
15%
PCM boost control 'B' driver circuit failure
Diagnostic Steps
1
Disconnect the boost solenoid 'B' and clear the code. With KOEO, monitor for the code to return — if it sets with the solenoid disconnected, the wiring has a short to ground.
2
Measure the solenoid coil resistance (10–30 ohms expected). Check for continuity between each solenoid pin and the solenoid body/ground — there should be no continuity.
3
With the solenoid and PCM disconnected, check the control wire for continuity to chassis ground — any continuity indicates a short in the harness.
4
Trace the harness from the solenoid to the PCM, inspecting for chafed insulation, melted wires near exhaust components, or crushed sections.
5
If the harness and solenoid test good, the PCM driver circuit may be pulling the line low — verify by measuring the control pin voltage at the PCM connector with the solenoid disconnected.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The PCM has detected that the turbocharger/supercharger boost control 'B' circuit voltage or signal is lower than expected. This points to a short to ground condition in the secondary boost control solenoid circuit. The driver will experience reduced turbo boost from the secondary system and possibl...
The most common cause of P004C (Turbocharger/Supercharger Boost Control "B" Circuit Low) is: Short to ground in the boost solenoid 'B' wiring harness
Typical repair costs for P004C range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe for limited driving at moderate speeds. The secondary boost system will not function properly, resulting in reduced power. Avoid situations requiring maximum power output. No immediate safety hazard but schedule repair to prevent further wiring damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P004C to identify the root cause.
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Quick Info
Category
Powertrain
System
Forced Induction / Turbocharger
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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