2008 Hummer H3 L5-3.7LFACTORY OEM SERVICE PROCEDURE

Oxygen Sensor: Locations




Engine Compartment Components

Factory service manual diagram



1 - Engine Control Module (ECM) X1
2 - Engine Control Module (ECM)
3 - Heated Oxygen Sensor (HO2S) 2 (LLR)
4 - Fuse Block - Underhood
5 - Engine Harness
6 - Heated Oxygen Sensor (HO2S) 1 (LLR)
7 - Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor
8 - Engine Control Module (ECM) X3
9 - Engine Control Module (ECM) X2



Right Rear of the Engine Components (LLR)

Factory service manual diagram



1 - Manifold Absolute Pressure (MAP) Sensor
2 - Throttle Body
3 - Ignition Coil 3
4 - Ignition Coil 2
5 - Ignition Coil 1
6 - Camshaft Position (CMP) Actuator Solenoid Valve
7 - Engine Oil Pressure (EOP) Switch
8 - Heated Oxygen Sensor (HO2S) 1
9 - Engine Coolant Temperature (ECT) Sensor
10 - Engine Coolant Temperature (ECT) Sensor Connector
11 - X101
12 - Ignition Coil 5
13 - Ignition Coil 4

Rear of the Transmission and Transfer Case Components (M30)

Engine Harness - Rear (M30):

Factory service manual diagram



1 - Transmission
2 - X175
3 - Heated Oxygen Sensor (HO2S) 2 Connector (LLR)
4 - Transfer Case Encoder Motor Connector
5 - Vehicle Speed Sensor (VSS) Connector
6 - Park/Neutral Position (PNP) Switch





Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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