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Home >> Pontiac >> 2001 >> Firebird Base, 2D Convertible, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0140: Ho2S Circuit Insufficient Activity - Bank 1, Sensor 2 >> Diagnostic Procedures

Diagnostic Procedures

  1. If powertrain diagnostic system check was performed, go to next step. If powertrain diagnostic system check was not performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under DIAGNOSTIC SYSTEM CHECKS. After performing powertrain diagnostic system check, go to next step.
    2. NOTE: If any DTCs except HO2S DTCs are present, repair those DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Start engine and run to normal operating temperature. Increase engine speed to more than 1200 RPM for 2 minutes. Using scan tool, select ENGINE 1 DATA LIST and monitor suspect HO2S voltage parameter. If voltage reading is 412-490 mV, go to next step. If voltage reading is not 412-490 mV, go to step  4.
  3. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 30 seconds. Start engine and operate vehicle within conditions required for diagnostic to run in code enable criteria, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC. If scan tool indicates that test failed this ignition, go to next step. If scan tool does not indicate that test failed this ignition, see INTERMITTENT TROUBLE CODE DETERMINATION  under SELF-DIAGNOSTIC SYSTEM.
  4. Check for exhaust leaks, incorrectly installed HO2S and damaged wiring. If problem was found and corrected, go to step  15. If no problems were found, go to next step.
  5. Turn ignition on. Disconnect HO2S. Jumper HO2S connector terminal "B" (Purple/White wire on Bank 1, Sensor 2; Purple wire on Bank 2, Sensor 1; Dark Blue wire on Bank 1, Sensor 2) to a good ground. Using scan tool, observe HO2S voltage parameter. If scan tool indicates HO2S voltage is more than 400 mV, go to next step. If scan tool indicates HO2S voltage is 400 mV or less, go to step  10.
  6. Remove jumper wire. Using a DVOM, measure voltage between ground and HO2S connector terminal "B" (Purple/White wire on Bank 1, Sensor 2; Purple wire on Bank 2, Sensor 1; Dark Blue wire on Bank 1, Sensor 2). If voltage is about 4.5 volts, go to next step. If voltage is not about 4.5 volts, go to step  9.
  7. Turn ignition on. Measure voltage at HO2S connector terminal "A" (Tan/White wire on Bank 1, Sensor 2; Tan wire on Bank 2, Sensor 1; Gray wire on Bank 1, Sensor 2). If voltage is about 5 volts, go to step  11. If voltage is not about 5 volts, go to next step.
  8. Check for open or high resistance in wiring between PCM and HO2S connector terminal "A" (Tan/White wire on Bank 1, Sensor 2; Tan wire on Bank 2, Sensor 1; Gray wire on Bank 1, Sensor 2). Repair as necessary. After repairs, go to step  15. If circuit is okay, go to step  13.
  9. Check for open or high resistance in wiring between PCM and HO2S connector terminal "B" (Purple/White wire on Bank 1, Sensor 2; Purple wire on Bank 2, Sensor 1; Dark Blue wire on Bank 1, Sensor 2). Repair as necessary. After repairs, go to step  15. If circuit is okay, go to step  13.
  10. Check for short to ground in wiring between PCM and HO2S connector terminal "A" (Tan/White wire on Bank 1, Sensor 2; Tan wire on Bank 2, Sensor 1; Gray wire on Bank 1, Sensor 2). Repair as necessary. After repairs, go to step  15. If circuit is okay, go to step  14.
  11. Check for poor connection at HO2S connector. Repair as necessary. After repairs, go to step  15. If connection is okay, go to next step.
  12. Determine cause of contamination before replacing HO2S.Check for alcohol/contaminants in fuel, excessive engine oil or coolant consumption, or use of improper RTV sealant. Remove HO2S and visually inspect sensor to check for contamination. If contaminated, portion of sensor exposed to exhaust stream will have a White powdery coating. Silicone contamination causes a high but false HO2S signal voltage (rich exhaust indication). PCM will then reduce amount of fuel delivered to engine, causing a severe driveability problem. Eliminate source of contamination before replacing oxygen sensor. Replace defective HO2S sensor. After repairs, go to step  15.
  13. Check for poor connection from HO2S wiring at PCM connector. Repair as necessary. After repairs, go to step  15. If connection is okay, go to next step.
  14. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - CARS article. After replacing PCM, go to next step.
  15. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine and allow it to reach normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step  2.
  16. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no undiagnosed DTCs are displayed, system is okay.
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