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Home >> Volvo >> 1995 >> 850 Base, 4D Sedan, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - Turbo >> Diagnostic Trouble Code Testing >> MOTRONIC 4.3 Control System >> Code 2-1-2: Front HO2S Signal

Code 2-1-2: Front HO2S Signal

  1. Check for other codes. If Code 5-2-1 is stored, diagnose that code first. If Code 5-2-1 is not stored, go to next step.
  2. If fault is permanent and signal is too high, go to next step. If fault is permanent and signal is too low, go to step 9). If fault is permanent and signal is absent, go to step 13). If fault is permanent and signal is faulty, go to step 19). If fault is intermittent and signal is too high, go to step 20). If fault is intermittent and signal is too low, go to step 21). If fault is intermittent and signal is absent, go to step 22). If fault is intermittent and signal is faulty, go to step 23).
  3. Turn ignition off. Connect breakout box between ECM and ECM connector. Turn ignition on. Connect voltmeter between breakout box pins No. 33 and 42. If voltmeter reads about .7 volt, go to step 6). If voltmeter does not read about .7 volt, go to next step.
  4. Turn ignition off. Disconnect front HO2S Black connector. Turn ignition on. Connect voltmeter between breakout box pins No. 33 and 42. If voltmeter reads about .7 volt, retest using new front HO2S. If voltmeter does not read about .7 volt, go to next step.
  5. Turn ignition off. Disconnect front HO2S connector. Disconnect rear HO2S Gray connector. Turn ignition on. Connect voltmeter between breakout box pins No. 33 and 42. If voltmeter reads about .7 volt, test using new rear HO2S. If voltmeter does not read about .7 volt, check wiring between front HO2S connector terminal No. 3 and ECM terminal A33, and wiring between rear HO2S connector terminal No. 3 and ECM terminal A19 for a short to voltage.
  6. Turn ignition on. Connect voltmeter between breakout box pins No. 32 and 42. If voltmeter reads about 1.2 volts, go to step 8). If voltmeter does not read about 1.2 volts, go to next step.
  7. Turn ignition off. Disconnect front HO2S Black connector. Turn ignition on. Connect voltmeter between breakout box pins No. 32 and 42. If voltmeter reads about 1.2 volts, test using new front HO2S. If voltmeter does not read about 1.2 volts, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32 for a short to voltage.
  8. Turn ignition off. Disconnect rear HO2S Gray connector. Turn ignition on. Connect voltmeter between breakout box pins No. 34 and 42. If voltmeter reads about zero volts, test using a new rear HO2S. If voltmeter does not read about zero volts, check wiring between rear HO2S connector terminal No. 4 and ECM terminal A34 for a short to voltage.
  9. If fault is permanent and signal is too low, connect breakout box to ECM. Turn ignition on. Connect voltmeter between breakout box pins No. 33 and 42. If voltmeter reads about .7 volt, go to step 12). If voltmeter does not read about .7 volt, go to next step.
  10. Turn ignition off. Disconnect front HO2S Black connector. Turn ignition on. Connect voltmeter between breakout box pins No. 33 and 42. If voltmeter reads about .7 volt, test using new front HO2S. If voltmeter does not read about .7 volt, go to next step.
  11. Turn ignition off. Disconnect front HO2S Black connector. Disconnect rear HO2S Gray connector. Turn ignition on. Connect voltmeter between breakout box pins No. 33 and 42. If voltmeter reads about .7 volt, test using new rear HO2S. If voltmeter does not read about .7 volt, check wiring between front HO2S connector terminal No. 3 and ECM terminal A33, and wiring between rear HO2S connector terminal No. 3 and ECM terminal A19 for a short circuit to ground.
  12. Turn ignition off. Disconnect front HO2S Black connector. Turn ignition on. Connect voltmeter between breakout box pins No. 32 and 42. If voltmeter reads about 1.2 volts, test using new front HO2S. If voltmeter does not read about 1.2 volts, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32 for a short circuit to ground.
  13. If fault is permanent and signal is absent, turn ignition off. Wait about 2 minutes. Disconnect front HO2S Black connector. Connect an ohmmeter between HO2S connector terminal No. 4 and ground. If ohmmeter reads about 50 k/ohms, go to step 15). If ohmmeter reads infinite resistance, go to next step. If ohmmeter reads about zero ohms, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32 for a short circuit to ground.
  14. Turn ignition off. Disconnect ECM. Disconnect front HO2S connector. Ensure ECM connector terminals are clean and tight. Reconnect ECM. Connect ohmmeter between HO2S connector terminal No. 4 and ground. If ohmmeter reads about 50 k/ohms, cause of code is poor contact at ECM connector. If ohmmeter does not read about 50 k/ohms, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32 for an open circuit.
  15. Turn ignition off. Disconnect front HO2S connector. Connect an ohmmeter between HO2S terminal No. 3 and ground. If ohmmeter reads infinite resistance, go to next step. If ohmmeter reads about zero ohms, go to step 17). If ohmmeter reads 200 ohms, go to step 18).
  16. Turn ignition off. Disconnect ECM. Disconnect front HO2S connector. Ensure ECM connector terminals are clean and tight. Reconnect ECM connector. Connect an ohmmeter between HO2S connector terminal No. 3 and ground. If ohmmeter reads about 200 ohms, source of code was poor contact in ECM connector. If ohmmeter does not read about 200 ohms, check wiring between front HO2S connector terminal No. 3 and ECM connector terminal A33 for an open circuit.
  17. Turn ignition off. Disconnect front HO2S Gray connector. Connect ohmmeter between front HO2S connector terminal No. 3 and ground. If ohmmeter reads about 200 ohms, retest using new rear HO2S. If ohmmeter does not read about 200 ohms, check wiring between front HO2S connector terminal No. 3 and ECM connector terminal A33, and wiring between rear HO2S connector terminal No. 3 and ECM connector terminal A19 for a short to ground.
  18. Turn ignition off. Ensure front HO2S is connected. Start and run engine at idle. Front HO2S should shift from its middle setting (.45 volt), and begin to vary between .1-.9 volt within minutes. If reading is okay, cause of code is poor contact in front HO2S connector. Ensure connector tabs are not damaged. If reading is incorrect, retest using new front HO2S.
  19. If fault is permanent and signal is faulty, turn ignition off. Wait about 2 minutes. Disconnect front HO2S Black connector. Connect an ohmmeter between HO2S connector terminals No. 3 and 4. If ohmmeter reads 50 ohms to infinite resistance, check wiring between front HO2S connector terminal No. 4 and ECM connector terminal A32 for a short circuit in wiring between front HO2S connector terminal No. 3 and ECM terminal A33. If ohmmeter does not read 50 to infinite ohms, test using new front HO2S.
  20. If fault is intermittent and signal is too high, check wiring between front HO2S connector terminal No. 4 and ECM connector terminal A32 for an intermittent short circuit to voltage. Also check wiring between front HO2S connector terminal No. 3 and ECM connector terminal A33, between rear HO2S connector terminal No. 3 and ECM terminal A19, and between rear HO2S connector terminal No. 4 and ECM terminal A34 for intermittent short to voltage.
  21. If fault is intermittent and signal is too low, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32, between front HO2S connector terminal No. 3 and ECM terminal A33, and between rear HO2S connector terminal No. 3 and ECM terminal A19 for an intermittent short to ground.
  22. If fault is intermittent and signal is absent, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32, and wiring between front HO2S connector terminal No. 3 and ECM terminal A33 for an intermittent open circuit. Check front HO2S and ECM connectors for a loose connection. Check wiring between front HO2S connector terminal No. 4 and ECM terminal A32, wiring between front HO2S connector terminal No. 3 and ECM terminal A33, and wiring between rear HO2S connector terminal No. 3 and ECM terminal A19 for an intermittent short circuit to ground.
  23. If fault is intermittent and signal is faulty, check wiring between front HO2S connector terminal No. 4 and ECM terminal A32 for an intermittent short circuit between front HO2S connector terminal No. 3 and ECM terminal A33.
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