Page 1 of 5 1Search Print Date: P0179 DTC P0179: Fuel Composition Sensor Circuit High Frequency Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptor DTC P0179 Fuel Composition Sensor Circuit High Frequency Circuit/System Description Alcohol content information is supplied to the engine control module (ECM) from the fuel composition sensor. The fuel composition sensor has a battery positive circuit, a signal circuit and a ground circuit. The fuel composition sensor uses a microprocessor inside the sensor to measure the ethanol percentage and changes the output signal accordingly. The signal circuit carries the ethanol percentage via the frequency signal. The ECM provides an internal pull up to 5 V on the signal circuit and the fuel composition sensor pulls the 5 V to ground in pulses. The normal range of operating frequency is between 50-150 Hz. The microprocessor inside the sensor is capable of a certain amount of self-diagnosis. An output frequency between 180 Hz and 190 Hz indicates that the fuel is contaminated. Conditions For Running The DTC The ignition voltage is greater than 11 V. The DTC runs continuously when the above condition is met. Conditions For Setting The DTC The engine control module detects that the fuel composition sensor output frequency is between 155-185 Hz for greater than 6 s. Action Taken When The DTC Sets DTC P0179 is a Type B DTC. Conditions For Clearing The MIL/DTC DTC P0179 is a Type B DTC. Diagnostic Aids A momentary slug of water in the fuel system may set this DTC. 2016 Chevrolet Impala 3.6L Eng LS

Page 2 of 5 Reference Information Schematic Reference Engine Controls Schematics (LFX) Engine Controls Schematics (LFR) Connector End View Reference COMPONENT CONNECTOR END VIEWS - INDEX Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Special Tools CH 44175-A Alcohol Tester Kit EL 38522-A Variable Signal Generator For equivalent regional tools, Refer to Special Tools (Diagnostic Tools) and Special Tools (Repair Tools) Circuit/System Verification 1. Engine running, 2. Verify the scan tool Fuel Composition Sensor parameter is between 50-150 Hz. 1. If not between 50-150 Hz Refer to Circuit/System Testing. 1. If between 50-150 Hz 3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. 4. Verify the DTC does not set. 1. If the DTC sets

Page 3 of 5 5. All OK. Circuit/System Testing Refer to Circuit/System Testing. 1. If the DTC does not set 1. Verify that there are no contaminants, water or too high of a concentration of ethanol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis and the CH 44175-A Instruction Manual. 2. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the B198 Fuel Composition Sensor. It may take up to 2 minutes for all vehicle systems to power down. 3. Test for less than 5 Ω between the ground circuit terminal 2 and ground. 1. If 5 Ω or greater 1. Ignition OFF. 2. Test for less than 2 Ω in the ground circuit end to end. 1. If less than 5 Ω 4. Ignition ON. 2. If less than 2 Ω, repair the open/high resistance in the ground connection. 5. Verify that a test lamp illuminates between the B+ circuit terminal 1 and ground. 1. If the test lamp does not illuminate and the circuit fuse is OK 1. Ignition OFF, remove the test lamp. 2. Test for less than 2 Ω in the B+ circuit end to end. 2. If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse. 1. If the test lamp does not illuminate and the circuit fuse is open 1. Ignition OFF, remove the test lamp. 2. Test for infinite resistance between the B+ circuit and ground. 1. If less than infinite resistance, repair the short to ground in the circuit. 2. If infinite resistance, replace the B198 Fuel Composition Sensor. 1. If the test lamp illuminates

Page 4 of 5 6. Ignition ON. 7. Test for 4.8-5.2 V between the signal circuit terminal 3 and ground. 1. If less than 4.8 V 1. Ignition OFF, disconnect the X1 harness connector at the K20 Engine Control Module. 2. Test for infinite resistance between the signal circuit and ground. 1. If less than infinite resistance, repair the short to ground in the circuit. 2. If infinite resistance 3. Test for less than 2 Ω in the signal circuit end to end. 2. If less than 2 Ω, replace the K20 Engine Control Module. 1. If greater than 5.2 V 1. Ignition OFF, disconnect the X1 harness connector at the K20 Engine Control Module. 2. Ignition ON. 3. Test for less than 1 V between the signal circuit and ground. 1. If 1 V or greater, repair the short to voltage on the circuit. 2. If less than 1 V, replace the K20 Engine Control Module. 1. If between 4.8-5.2 V 8. Ignition OFF, connect the red lead of the EL 38522-A Variable Signal Generator to the signal circuit terminal 3 at the B198 Fuel Composition Sensor harness connector. 9. Connect the battery voltage supply to B+ and the black lead to ground. 10. Set the EL 38522-A Variable Signal Generator Signal to 5 V, the Frequency to 60 Hz and the Duty Cycle to Normal. 11. Ignition ON. 12. Clear the DTCs with a scan tool. 13. Verify the scan tool Fuel Composition Sensor parameter is at 60 Hz. 1. If not the specified value Replace the K20 Engine Control Module. 1. If the specified value

Page 5 of 5 14. Test or replace the B198 Fuel Composition Sensor. Component Testing 1. Test the fuel composition using the CH 44175-A Alcohol Tester Kit and the CH 44175-A Instruction Manual. Record the frequency. 2. Compare the special tool test frequency and the scan tool Fuel Composition Sensor frequency parameter. 3. Verify the difference between the tool and the sensor is 12 Hz or less. 4. All OK. Repair Instructions 1. If greater than the specified value Replace the B198 Fuel Composition Sensor. 1. If less than the specified value Perform the Diagnostic Repair Verification after completing the repair. Flexible Fuel Sensor Replacement Fuel System Cleaning Control Module References for K20 Engine Control Module replacement, programming and setup.