856831 1 Mercury CLAMP

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 Data LinkThe compressor bypass actuator sends the following information to the ECM via the CAN data link:
Actual position of the actuator
Desired position of the actuator
Temperature of the actuator electronics
Diagnostic informationIf the ECM cannot communicate with the actuator via the CAN data link, the ECM activates a 1720-9 diagnostic code and the event is logged.A 1720-9 diagnostic code is probably caused by a problem with an electrical connector or a harness. The next likely cause is a problem with the actuator or a problem with the power circuit for the actuator. The least likely cause is a problem with the ECM. Refer to Troubleshooting, "CAN Data Link - Test" for information that is related to troubleshooting the 1720-9 diagnostic code.Self-diagnostic FunctionIf an internal fault is detected by the actuator, the condition is communicated via the CAN data link. The ECM activates a 1720-12 diagnostic code and the engine is shut down. The most likely cause of a 1720-12 diagnostic code is a problem with the actuator.
Illustration 2 g02148097
Schematic for the circuit of the compressor bypass actuatorTest Step 1. Inspect the Electrical Connectors and Wiring
Set the engine control switch to the OFF/RESET position. Remove the electrical power from the engine.
Illustration 3 g01768637
Locations of the connectors at the ECM junction box that are for the compressor bypass actuator (3) J1/P1 ECM connectors (4) Control harness connector for the wiring to the compressor bypass actuator
Illustration 4 g01768635
Locations of the connectors at the engine junction box that are for the compressor bypass actuator (5) Power harness connector at the engine junction box (6) Engine interface connector at the engine junction box (7) Interconnect harness connectors
Illustration 5 g01768633
Connections at the engine junction box that are for the compressor bypass actuator (left side engine view) (F6) 10 amp fuse for the compressor bypass actuator
Thoroughly inspect the harness connectors for compressor bypass actuator (1) . Also, check the mechanical condition of bypass valve (2) . Check the full travel of the valve for binding. Inspect the condition of connectors (3) , (4) , (5) , (6) , and (7) . Also, inspect fuse (F6) for good repair. Ensure that the power connections that are for the terminal strip in the engine junction box are tight and free of corrosion. Refer to Troubleshooting, "Electrical Connectors - Inspect".
Illustration 6 g01779610
Terminal connections at the P1 connector that are for the compressor bypass actuator (P1-34) CAN data link - (P1-42) CAN shield (P1-50) CAN data link + (P1-59) PWM signal (P1-60) Return