RING-RETAINING 3P3441 - Caterpillar

System Operation Description:Use this procedure to troubleshoot a problem with the compressor bypass actuator. Also use this procedure if one of the diagnostic codes in Table 1 are active or easily repeated.
Table 1
Diagnostic Codes Table    
Description    Conditions which Generate this Code    System Response    
1720-8 Turbocharger Compressor Bypass Valve Actuator : Abnormal Frequency, Pulse Width, or Period     The compressor bypass actuator has detected an error in the Pulse Width Modulated signal (PWM) that is from the Electronic Control Module (ECM).     The code is logged.
The alarm output is activated.    
1720-9 Turbocharger Compressor Bypass Valve Actuator : Abnormal Update Rate     The ECM has lost the last four messages that were expected from the compressor bypass actuator over the CAN data link.     The code is logged.
The alarm output is activated.
The shutdown output is activated.
The engine is shut down.    
1720-12 Turbocharger Compressor Bypass Valve Actuator : Failure     The compressor bypass actuator has reported that an internal fault has occurred.    The strategy for the compressor bypass actuator enables the ECM to maintain the desired boost pressure during all engine operating conditions.
Illustration 1 g01768214
Flow of the compressed air/fuel mixture (top side engine view) (1) Compressor bypass actuator (2) Compressor bypass valveThe signal for compressor bypass actuator (1) is generated by calculating the desired boost pressure for the engine. The ECM uses the actual boost pressure and a map that uses information from various engine parameters in order to calculate the desired boost pressure. The ECM then compares the actual boost pressure to the desired boost pressure. A command signal is sent to the actuator in order to control the movement of the compressor bypass actuator shaft. As the signal varies, the shaft travel causes bypass valve (2) to regulate the amount of bypass at a proportional rate. The amount of bypass regulates the amount of boost pressure that is available to the engine.The compressor bypass valve is mounted on the aftercooler housing at the outlet of the aftercooler. This location allows the compressor bypass to reduce the boost that is available at the inlet of the throttle plate. When the bypass valve is opened, the compressor bypass dumps the compressed air/fuel mixture from the aftercooler housing. The compressed air/fuel mixture is dumped directly into the inlet piping of the turbocharger compressor. The boost pressure that is available to the fuel metering valve is effectively reduced.The ECM modulates the bypass valve from a fully closed position to a fully opened position.The compressor bypass is also operated when the engine is shut down. Reducing the boost during the shutdown reduces the opportunity for a turbocharger surge.CommunicationsThe ECM sends the following information to the compressor bypass actuator:
Desired position of the actuator
PWM signal for desired position of the actuatorPWM SignalThe ECM sends the command signal for the position of the compressor bypass actuator via a PWM signal. If this PWM signal is interrupted, a 1720-8 diagnostic code will be activated. The ECM will shut down the engine.CAN