Error messages with the designation “Boost pressure regulator/boost pressure controller defective” indicate a deviation of the actual setpoint from the target setpoint. Such a malfunction results in partial emergency operation of the boost pressure control. In modern turbocharged diesel engines, boost pressure is controlled by an electric actuator on the control linkage of the VTG turbine.
Causes of the malfunction can be stuck turbocharger control linkages, stuck VTG units in the turbocharger, and defective boost pressure controllers.
The following error codes are possible for specific brands:
| Brand |
Fault code |
Fault description |
| BMW |
299F00 |
Boost pressure regulator, position control: Boost pressure regulator too open/control deviation |
| Ford/Jaguar |
P132A / P132B |
Turbocharger boost pressure control A: electrical fault |
| Mercedes-Benz |
P126800 |
Y77/8 boost pressure regulator defective |
| Mercedes-Benz |
P2510 |
Boost pressure regulator, component defective |
| Mercedes-Benz |
P2510-001 |
Check boost pressure regulator |
| PSA |
P0299 |
Boost pressure control: Control deviation |
| VW/AUDI |
P1952 / 06482 |
Turbocharger control module 1 – defective |
System description
In modern turbocharged diesel engines, boost pressure is controlled by an electric actuator on the control linkage of the VTG turbine. This has significantly increased the speed and precision of the control system.
The boost pressure controller has a servomotor, a worm gear, a contactless inductive CIPOS sensor for position feedback, and a control unit with a communication module.
Manufacturers use two variants of boost pressure controllers.
| Variant |
Type of regulation |
| Smart |
The position of the actuator is controlled autonomously according to the specifications of the engine control unit and then transmits a status message to the engine control unit. |
| Simple |
The engine control unit directly controls the actuator in a circuit. The internal electronics of the control module only transmit the status message for this purpose. |
Fault description
Error message “Boost pressure regulator/boost pressure controller defective”
An internal diagnostic sequence monitors the control system and the component for malfunctions and transmits these to the engine control unit. In the event of restrictions in the actuator function, with the exception of the internal mechatronics self-monitoring, it cannot distinguish whether these are caused by an internal or external defect.
The system monitors internal components, communication with the engine control unit, the power supply, and the current at the servomotor. If the actuator does not reach the required position within the specified time with the assigned actuator current, the actuator module transmits this in the form of a status message to the engine control unit.
An error code is set and the emergency run program is started.
Further actions depend on the applications, which are the responsibility of the system and vehicle manufacturers. Manufacturers define diagnostic information with a wide variety of error codes. Extensions with subtexts specify the information.
Possible causes:
- Control device linkage or guide vanes sluggish or stuck
- Corrosion of internal electrical and electronic components due to environmental influences (water, salt, oil, fuel)
- Mechanical damage due to external influences, installation errors
- Sporadic or permanent supply voltage deficiency
Consequences of the error
If sporadic problems occur in the area of boost pressure, an error code relating to boost pressure control is stored in the error memory. In this case, the vehicle only has reduced power and the engine warning light often comes on. After changing the ignition, the engine often runs normally again until the next time the fault occurs.
In the event of a fault, the VTG turbine is switched to emergency mode. This means that the guide vanes remain in the fully open position, which corresponds to a reduction in torque. The high speed still possible due to the volume flow is prevented by the emergency mode map in the engine management system via a reduction in the injection mass.
Since the exhaust gas temperature drops during the emergency mode phase and combustion is negatively affected, the amount and size of particles in the exhaust gas stream increases. The result is an increasing load on the particulate filter and an increase in exhaust gas back pressure. Under these conditions, regeneration of the particulate filter is difficult. This leads to an accumulation of regeneration interruptions until this function is blocked in the engine control unit.
The soot loading factor in the engine oil increases and the interval counter runs up faster. During the emergency mode phase, the noise emission of the charge air system and the shifting behavior of the automatic transmission change.
Possible emergency strategy
- Torque and speed reduction
- Shift point change in automatic transmission
- Engine malfunction indicator light (MIL) illuminates
- Start & Stop function is hidden
Diagnosis/measurements/repair
A defect in the turbocharger actuator is often preceded by a defect in the guide vane adjustment on the turbocharger. Over time, the exhaust gas flow causes heavy contamination on the hot gas side of the turbocharger. This particle formation on the leading edges of the VTG adjustment mechanism restricts the mobility of the guide vanes. Mechanical sluggishness leads to increased axial load and higher adjustment effort for the entire actuator. The required higher torque can only be compensated for by the servomotor in the turbocharger actuator with higher power consumption. The consequences are higher thermal stress on the electronics and ultimately significantly higher friction in the worm gear drive.
The diagnosis can be made in two ways:
• Metrological-electrical diagnosis
• Mechanical diagnosis
Sample from the current curve (blue) and voltage curve (red) recorded when the boost pressure regulator reaches its end position in the actuator test with the diagnostic device. On the red current curve, the values shown in the red boxes are close to the limit at 4.6-5.4A in the end position. The current consumption should not exceed 2.6A during normal positioning. The voltage shown in blue drops to 10.3V at the moment of impact. The tested system is still fault-free, although the values indicate a problem in the medium term.
Mechanical diagnosis
Ideally, after removing the boost pressure regulator, the smoothness of the VTG turbine control lever should be checked. This should be done while the turbocharger is still hot, as experience has shown that the VTG mechanism tends to become sluggish in this state. The increased control torques are to be understood as the cause. This problem must be rectified before installing a repaired boost pressure regulator. This method can also be used for diagnosis without first removing the boost pressure regulator, provided that space permits.
Check for mechanical wear on the boost pressure regulator
On the dismantled boost pressure regulator, the eccentric bolt for the control lever must have 0.5 mm of play in the regulator. Greater play indicates a worn worm gear. Repair is necessary. This play must always be considered in relation to the mileage of the turbocharger.
Diagnostic information for Mercedes Benz V engines
The subtext for the error code must not differ from the one specified here. Texts such as “circuit faulty” indicate a fault in the voltage supply to the boost pressure regulator. This must be measured on the component when the fault occurs. The servomotor for the intake manifold shut-off (EKAS) is often the cause. Both components share the power supply for both potentials, and the positive potential is also shared with the exhaust gas recirculation cooling solenoid valve. The unfavorable mounting position of the EKAS servomotor below the turbocharger’s fresh air duct leads to oil contamination as a result of a defective seal. The servomotor leaks oil heavily and, as a result of the increased current consumption, sporadically pulls the voltage potential below the threshold value. Since monitoring the boost pressure control is a priority, the fault is first set there. The current consumption usually remains below the fuse’s trigger threshold because the high load only occurs temporarily.
Installation instructions
Most systems do not provide a calibration option/basic setting, as manufacturers do not approve repairs to the component.
The movement of the linkage should be checked again before installation. The intermediate rod must not be adjusted. Axial compensation bearings should be treated with high-temperature lubricating paste if necessary. If there is some play in the fastenings of the boost pressure regulator with slightly flush-mounted screws, this should be used to fasten the boost pressure regulator at the upper stop, opposite the lever position in the torque position. If, after the test drive, an error in the boost pressure control is again stored with reference to an incorrect stop position, the boost pressure regulator must be loosened and fixed in the opposite position in the fastenings.
Damage to this component related to the described fault with repair option following brands:
