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√ Low Atmospheric Pressure (Diagnostic Code: 106-1)

CID 106 - FMI 01 (Engine Derate/ RPM Hunting) on CAT-3512 Engine
Figure 1.1 - Low Atmospheric Pressure (26)

Conditions which generate this code:
The Right or Left Turbocharger Inlet Pressure Sensors indicate Low Atmospheric Pressure. This can be caused by excessive air filter restriction or operation at altitude above 1500 meters (5000 ft)

System Responses:
The diagnostic code is active and logged. Engine power is derated while diagnostic code 106-01 is active.

Troubleshooting:
P-529 - Turbocharger Inlet Pressure Sensors.

System Operation:
The ECM monitors turbocharger inlet (atmospheric) pressure with sensors (located on the left and right air cleaner housing). The Turbocharger Inlet Pressure Sensors receive a +5 VDC supply voltage from the ECM and provides a DC output voltage signal that is proportional to Inlet air pressure. The sensors have an operating range of 0-116 kpa (0-16.8 psi) absolute. The ECM uses signals from the Turbocharger Inlet Pressure Sensors to protect the engine by derating engine power when high altitude or high inlet restriction condition exist.
Engine derate is based on the lower of the two Turbocharger Inlet Pressure Sensors reading. If one of the sensor signals is diagnosed as faulty, a diagnostic code is generated and the other sensor signal is used to determine engine power derate. If both sensor signals are faulty, no derate occurs. Read More: Absolute Pressure on Caterpillar ET Software.
Figure 1.2 - Incorrect Boost and Engine Oil Pressure 

The ECM subtracts Turbocharger Inlet Pressure from Inlet Manifold (Boost) Pressure and Engine Oil Pressure for gauge pressure indication on an Electronic Service Tool. Failure of both Turbocharger Inlet Pressure Sensors results in incorrect Boost and Engine Oil Pressure Electronic Service Tool readings.
Figure 1.3 - Turbocharger Inlet Pressure Sensors Schematic

Functional Test
Step 1. Inspecting Electrical Connectors and Wiring
A. Turn the Engine Control Switch to the OFF position.
B. Check that Turbocharger Inlet Pressure Sensors Connectors J5/P5 and J6/P6, MUI Interface Connector J15/P15, and ECM Connector J14/P14 are securely mated and free of damage and corrosion. Check Allen Screws for proper torque.
C. Check the wiring and harness for abrasion and pinch points from the Turbocharger Inlet Pressure Sensors back to the ECM.
D. Perform a 45 N (10 lb) Pull Test on each wire.

Step 2. Check for Active Diagnostic Codes
A. Turn the Engine Control Switch to the ON position.
B. Connect an Electronic Service Tool at the Service Tool Connector. Read More: How to Connecting Caterpillar ET Software to the ECM.
C. Check for an Active 68-03, 106-03, 68-04, or 106-04 diagnostic code. In this case, only 1 active diagnostic code: Low Atmospheric Pressure (106-01), but sometimes found Error Code: 102-4 Boost Pressure voltage low (25), 241-1 5 Volt Short Circuit (21), and 111-1 Low Coolant Level Warning (62).
  • 102-04 - The Boost Sensor signal voltage is less than 0.75 VDC and there are no Sensor Supply Voltage diagnostic codes.
  • 111-01 - The Coolant Level Sensor has detected low coolant level for more than 10 seconds, the engine has been running at least 30 seconds, and there are no active Sensor Supply Voltage diagnostic codes.
  • 241-01 - The supply voltage for +5VDC sensor is less than 3 VDC or greater than 7.0 VDC.
Figure 1.4 - Error Code: 102-4 and 111-1
Figure 1.5 - Error Code: 111-1 and 241-1

E. Check the Inlet Manifold (Boost) Pressure Sensor (damaged: broken) and Coolant Level Sensor (damaged: no resistance).
Figure 1.6 - Boost Pressure Sensor (damaged: broken)
F. After replaced Boost Pressure Sensor and Coolant Level Sensor, Error Code: 68-4 Secondary Atmospheric Pressure Signal voltage low, and 110-4 Coolant Temperature voltage low occurs (while engine is running).
  • 68-04 - The Right or Left Turbocharger Inlet Pressure Sensors signal voltage is less than 0.2 VDC for at least 1 second and there are no Sensor Supply Voltage diagnostic codes.
  • 110-04 - Coolant Temperature short active. The Coolant Temperature Sensor signal voltage is less than 0.3 VDC and there are no Sensor Supply Voltage diagnostic codes.

Step 3. Check Supply and Signal Voltage At All Pressure and Temperature Sensors
A. Disconnect the Sensors connector, and measure supply voltage (between pin A and B) and Pull-Up voltage (between pin B and C). In this case, any sensors only measured 2.2 VDC supply voltage from the ECM (expected results: 5 VDC for Analog Sensors, and 8 VDC for Digital Sensors), but the Pull-Up voltage are OK.  Read More: PULL-UP Voltage and How the ECM Uses it to Determine Diagnostic Conditions.
B. Finally, replaced the ECM Module + Personality IC Program (waiting ordered: for 3 months).
Figure 1.7 - ECM and MUI Interface Module

Figure 1.8 - Personality IC Program (inside the ECM)


Read More:
PTO Throttle Signal Invalid (Error Code: SPN 644 - FMI 8)
PTO Configurations for On-Highway Truck (Caterpillar Engines)