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P11C4





DTC P11C2-P11C4

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P11C2
- Intake Air Humidity Sensor Circuit Low Voltage

DTC P11C3
- Intake Air Humidity Sensor Circuit High Voltage

DTC P11C4
- Intake Air Humidity Sensor Circuit Erratic

Diagnostic Fault Information










Typical Scan Tool Data










Circuit/System Description

The humidity sensor measures the ambient humidity of the air in the sensor bore. The signal varies with intake air humidity and is displayed by the scan tool as duty cycle %. The ECM applies 5 V to the circuit. The signal circuit is shared by the humidity sensor and the intake air temperature (IAT) sensor 2. Ignition voltage and ground circuits are also supplied to the multifunction intake air sensor's internal circuits for these sensors:

* IAT sensor 2

* Humidity sensor

* MAF sensor

The multifunction intake air sensor houses the following:

* IAT sensor 1

* IAT sensor 2

* Humidity sensor

* MAF sensor

* BARO pressure sensor

Conditions for Running the DTCs

P11C2, P11C3, and P11C4

* DTC P1682 is not set

* The ignition is ON.

* The Ignition signal is at least 11 V for longer than 0.9 s.

* These DTCs run continuously within the enabling conditions.

Conditions for Setting the DTCs

P11C2

The ECM detects that the sensor signal is less than or equal to 5 % for greater than 5 s.

P11C3

The ECM detects that the sensor signal is greater than or equal to 95 % for greater than 5 s.

P11C4

The ECM monitors the sensor signal every 0.1 s, to determine if the signal has changed more than 40 % during a 4 s time period.

Action Taken When the DTC Sets

DTCs P11C2, P11C3, P11C4 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P11C2, P11C3, P11C4 are Type B DTCs.

Diagnostic Aids

* The Intake Air Humidity Signal parameter displays the measured humidity within the air intake system and may differ from atmospheric humidity measured outside the air intake system.

* The humidity sensor and the IAT sensor 2 signals are sent to the ECM on the same circuit. If the Intake Air Humidity parameter displays the value: 0 % or 100 %, and there are also IAT Sensor 2 DTCs, check for a circuit problem.

Reference Information

Schematic Reference

Engine Controls Schematics [1][2]Electrical Diagrams

Connector End View Reference

Component Connector End Views Sunshade - Left

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References Control Module References for scan tool information

Special Tools

EL-38522 - Variable Signal Generator

For equivalent regional tools, refer to Special Tools Tools and Equipment.

Circuit/System Verification

Note: To minimize the effects of residual engine heat and sensor internal heating elements, perform Steps 1 and 2 of this verification procedure only if the ignition has been OFF for 8 hours or more.

1. Ignition ON.

2. Verify the following scan tool parameters are within 30°C (54°F) of each other.

* Start-Up IAT Sensor 1

* IAT Sensor 2

* IAT Sensor 3; where equipped

• If not within 30°C (54°F)
Refer to Circuit/System Testing.

• If within 30°C (54°F)

3. Engine idling, verify the scan tool Intake Air Humidity parameter is between 5 and 90 %.

• If not between 5 and 90 %
Refer to Circuit/System Testing.

• If between 5 and 90 %

4. 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.

5. Verify the DTCs do not set.

• If any of the DTCs set
Refer to Circuit/System Testing.

• If none of the DTCs set

6. All OK

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B75C Multifunction Intake Air sensor.

2. Ignition OFF, all systems OFF. It may take up to for 2 minutes for all vehicle systems to power down. Test for less than 2 ohms between the low reference circuit terminal 3 and ground.

• If 2 ohms or greater

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.

2. Test for less than 2 ohms in the low reference circuit end to end.

• If 2 ohms or greater, repair the open or high resistance in the circuit.

• If less than 2 ohms replace the K20 Engine Control Module.

• If less than 2 ohms

3. Ignition OFF, all vehicle systems OFF, test for less than 2 ohms between the ground circuit terminal 7 and ground.

• If 2 ohms or greater

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open or high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 2 ohms

4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 5 and ground.

• If the test lamp does not illuminate and the circuit fuse is good

1. Ignition OFF, remove the test lamp and remove the fuse for the ignition voltage circuit.

2. Test for less than 2 ohms in the ignition voltage circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.

• If the test lamp does not illuminate and the circuit fuse is open

1. Ignition OFF, remove the test lamp and remove the fuse for the ignition voltage circuit.

2. Test for infinite resistance between the ignition voltage circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for greater than 2 ohms between the ignition voltage circuit terminal 5 and ground.

• If less than 2 ohms, repair the short to ground on the circuit.

• If greater than 2 ohms, test all the components connected to the circuit and repair or replace as necessary.

• If a test lamp illuminates

5. Ignition ON, test for 4.8-5.2 V between the humidity signal circuit terminal 8 and ground.

• If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.

2. Test for infinite resistance between the signal circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohms in the signal circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, replace the K20 Engine Control Module.

• If greater than 5.2 V

Note: If the signal circuit is shorted to a voltage the engine control module or the sensor may be damaged.

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.

2. Ignition ON, test for less than 1 V between the signal circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V, replace the K20 Engine Control Module.

• If between 4.8-5.2 V

6. Ignition OFF, connect the leads of the EL-38522 - Variable Signal Generator as follows:

* Red lead to the signal circuit terminal 8 at the harness connector

* Black leads to ground

* Battery voltage supply lead to B+

7. Set the EL-38522 - Variable Signal Generator to the following specifications.

* Signal switch to 5 V

* Frequency switch to 250 Hz

* Duty Cycle switch to 50 % (Normal)

8. Ignition ON, observe the scan tool Intake Air Humidity parameter. The scan tool parameter should be between 45-55 %.

• If not between 45-55 %.
Replace the K20 Engine Control Module.

• If between 45-55 %.

9. Test or replace the B75C Multifunction Intake Air sensor.

Component Testing

Multifunction Intake Air Sensor

1. Test the Intake Air Humidity Sensor by varying the air humidity in the intake duct near the sensor, while observing the scan tool Intake Air Humidity Sensor parameter. The parameter should change and be within 5-95%.

• If not within the specified range
Replace the B75C Multifunction Intake Air sensor

• If within the specified range

2. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* Mass Airflow Sensor with Intake Air Temperature Sensor Replacement (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) Service and Repair for multifunction intake air sensor replacement

* Control Module References Control Module References for engine control module replacement, programming, and setup

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