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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 155 (Engine Controls Self-Diagnostics - 5.7L - Bi-Fuel) >> Diagnostic Tests >> DTC P0135 & P0155: Ho2S Bank 1& 2 Sensor 1 Heater Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
    2. NOTE: The HO2S must be cool before proceeding with this diagnosis. The ignition must remain OFF for at least one half hour before proceeding with the diagnosis.
  2. Connect a scan tool. Set-up the scan tool with the proper vehicle identification information prior to turning the ignition ON. Establish communication with the PCM for this step. Turn the ignition ON, with the engine OFF, and as quickly as possible observe and record the HO2S voltage for the sensor that applies to this DTC. Observe the HO2S voltage for 2 minutes. Does the HO2S voltage increase or decrease from the initial voltage by at least 150 mV? If yes, go to next step. If no, go to step  6 .
  3. Allow the HO2S voltage to stabilize. Use the scan tool in order to observe and record the current HO2S voltage from the PCM. Use the scan tool in order to establish communication with the AF ECM. Use the scan tool in order to observe and record the current voltage for the HO2S sensor that applies to this DTC. Does the AF ECM indicate the same HO2S voltage as the PCM, plus or minus 45 mV? If yes, go to next step. If no, go to step  14 .
  4. The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
    • An intermittently open or high resistance HO2S high signal circuit or low circuit.
    • An intermittently open or high resistance HO2S heater ignition feed or ground circuit.
    • A faulty HO2S or PCM connector terminal contact.
    • A defective HO2S.

    Repair any of the above conditions as necessary. Was a condition found and repaired? If yes, go to step  18 . If no, go to next step.

  5. The fault is not present. See DIAGNOSTIC AIDSDiagnostic Aids  . Are any DTCs stored that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  6. Turn the ignition OFF. Disconnect the HO2S connector for the sensor that applies to this DTC. Connect the Unpowered Test Lamp (J 34142-B) between the HO2S heater ignition feed and ground circuit terminals, engine harness side. Turn the ignition ON, with the engine OFF. Does the test lamp illuminate? If yes, go to next step. If no, go to step  8 .
  7. Disconnect the test lamp. Jumper the HO2S low circuit terminal to a known-good ground. Jumper the HO2S high signal circuit terminal to a known-good ground. Use the scan tool in order to monitor the HO2S voltage for the sensor that applies to this DTC. Ensure that the ignition is ON while the engine is OFF. Is the voltage less than 20 mV? If yes, go to step  10 . If no, go to step  9 .
  8. Connect the test lamp between the HO2S heater ignition feed circuit terminal (engine harness side) and a known-good ground. Ensure that the ignition is ON while the engine is OFF. Does the test lamp illuminate? If yes, go to step  11 . If no, go to step  12 .
  9. Turn the ignition OFF. Remove the jumpers from the HO2S terminals. Disconnect the PCM connector containing the HO2S high and low circuits. Use a Digital Multimeter (DMM) in order to measure the continuity of the HO2S high signal circuit and the HO2S low circuit between the PCM connector terminal and the HO2S connector terminal, engine harness side. Are both resistances less than 5 ohms? If yes, go to step  16 . If no, go to step  13 .
  10. Replace the HO2S sensor. See OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE. After repairs, go to step  18 .
  11. Repair the open HO2S heater ground circuit. After repairs, go to step  18 .
  12. Repair the lack of power on the HO2S heater ignition feed circuit. If the fuse is open, repair the short to ground on the circuit. An open fuse or lack of power to the fuse may cause other DTCs or symptoms to be present. After repairs, go to step  18 .
  13. Repair the circuit that measured high resistance. After repairs, go to step  18 .
  14. Inspect the oxygen sensor signal and low circuit for continuity between the AF ECM connector terminals and the oxygen sensor connector terminals. Inspect these circuits for shorts to other circuits or to ground. Ensure that the oxygen sensor, PCM and the AF ECM connectors are disconnected before testing circuits. Repair the wiring as necessary. Was a wire repair made? If yes, go to step  18 . If no, go to next step.
  15. Replace AF ECM. See ALTERNATE FUEL ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. Program (flash) AF ECM with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL MODULE  under PROGRAMMING. After repairs, go to step  18 .
  16. Inspect for proper PCM terminal contact. Repair the terminals as necessary. Was a terminal repair made? If yes, go to step  18 . If no, go to next step.
    17. NOTE: The following control module replacement procedures must all be completed before attempting to operate the vehicle.
  17. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE. Program (flash) PCM with correct vehicle software and calibration. See POWERTRAIN CONTROL MODULE REPROGRAMMING  under PROGRAMMING. To perform CKP variation learn procedure, a switchover to gasoline operation is necessary. Remove CNG fuse (20-amp) located in underhood fuse block to perform switchover. Perform CKP system variation learn procedure. See CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE  under PROGRAMMING. After performing repairs and procedures, go to next step.
    18. NOTE: The HO2S must be cool before proceeding with this diagnosis. The ignition must remain OFF for at least one half hour before proceeding with the diagnosis.
  18. Connect a scan tool. Set-up the scan tool with the proper vehicle identification information prior to turning the ignition ON. Turn the ignition ON, with the engine OFF, and as quickly as possible observe and record the HO2S voltage for the sensor that applies to this DTC. Observe the HO2S voltage for 2 minutes. Does the voltage increase or decrease from the initial voltage by at least 150 mV? If yes, system is okay. If no, go to step  2 .
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