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Home >> Isuzu >> 1998 >> Trooper S, Standard >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Tests W/Codes - 3.2L & 3.5L >> Self-Diagnostic Tests >> DTC P0140: Heated Oxygen Sensor (Ho2S) No. 2 Bank 1/Insufficient Activity >> Diagnostic Aids

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

Using scan tool, monitor signal voltage while wiggling HO2S related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage to a fixed voltage. A change in voltage will assist in isolating location of fault. DO NOT  solder HO2S wires.

  1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
  2. Start engine and allow it to reach normal operating temperature. Apply parking brake and increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, observe HO2S No. 2, bank 1 parameter. If reading is 425-475 mV, go to step 4). If reading is not 425-475 mV, turn engine off and go to next step.
  3. Turn ignition on. Review and record FAILURE RECORDS data on scan tool. Operate vehicle within FAILURE RECORDS conditions. If DTC P0140 is set, go to next step. If DTC P0140 is not set, check for an intermittent problem, see DIAGNOSTIC AIDS  .
  4. Check for poor high or low signal circuit (Blue and Green wires - 3.2L; Red and White wires - 3.5L) connections at HO2S No. 2, bank 1 harness connector or damaged harness. Repair as necessary. Retest system. If connection is okay, go to next step.
  5. Turn ignition off. Disconnect PCM harness connectors. Check for poor HO2S No. 2, bank 1 high or low signal circuit (Blue and Green wires - 3.2L; Red and White wires - 3.5L) connections at PCM harness connectors or damaged harness. Repair as necessary. Retest system. If connections are okay, go to next step.
  6. Turn ignition off. Measure resistance of HO2S No. 2, bank 1 high and low signal circuits between PCM and HO2S. If resistance is greater than 5 ohms in either wire, repair open or poor connection. Retest system. If wire is okay, go to next step.
  7. Turn ignition on. Disconnect HO2S No. 2, bank 1 connector. Connect fused jumper wire between high and low signal circuit of HO2S No. 2, bank 1 (PCM side) and ground. If scan tool display is 0-10 mV, replace HO2S No. 2, bank 1. If display is not as specified, replace PCM. Retest system.
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