LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Dodge and Ram >> 1998 >> Caravan Base, 2.4 B >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 2.4L >> DTC Test >> Test TC-129A - Downstream O2 Sensor Stays At Center
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test TC-129A - Downstream O2 Sensor Stays At Center

NOTE: For connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article.
  1. If downstream oxygen sensor voltage is between .35 volt and .58 volt for 30 seconds, the Powertrain Control Module (PCM) pulls sensor voltage to 5 volts for 60 seconds and monitors the sensor voltage. If voltage is greater than 1.5 volts for 2 consecutive trips, DTC will be stored in PCM. Possible causes are: sensor output wire open, open ground circuit, defective downstream oxygen sensor, defective connector terminals or wiring, dirt/moisture or grease inside connector, or defective PCM. Go to next step.
  2. Turn ignition on with engine off. Wait 3 minutes and then use scan tool to monitor downstream oxygen sensor voltage for a few minutes. Once downstream oxygen sensor voltage stabilizes between .4 and .6 volt, use scan tool to actuate downstream oxygen sensor heater test while monitoring downstream oxygen sensor voltage for at least 2 minutes.
  3. If downstream oxygen sensor voltage does not remain at .4-.6 volt, go to next step. If downstream oxygen sensor voltage remains at .4-.6 volt, go to step  6.
  4. Stop downstream oxygen sensor heater test. Turn ignition off. Disconnect connector at downstream oxygen sensor. Downstream oxygen sensor is mounted on exhaust pipe behind catalytic converter. Inspect connector for pushed out, miswired or damaged terminals. If terminals are not pushed out, miswired or damaged, go to next step. If terminals are pushed out, miswired or damaged, repair connector as necessary. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES .
  5. Using ohmmeter, check resistance between ground and terminal No. 3 (Black/Light Blue wire) on wiring harness side of connector for downstream oxygen sensor. If resistance is 5 ohms or more, repair open circuit in Black/Light Blue wire between PCM and downstream oxygen sensor. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES . The PCM is located between driver's side front fender and power distribution center, near battery. If resistance is less than 5 ohms, replace downstream oxygen sensor. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES .
  6. Stop downstream oxygen sensor heater test. Turn ignition off. Disconnect connector at downstream oxygen sensor. Downstream oxygen sensor is mounted on exhaust pipe behind catalytic converter. Inspect connector for pushed out, miswired or damaged terminals. If terminals are not pushed out, miswired or damaged, go to next step. If terminals are pushed out, miswired or damaged, repair connector as necessary. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES .
  7. Using ohmmeter, check resistance between ground and terminal No. 3 (Black/Light Blue wire) on wiring harness side of connector for downstream oxygen sensor. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit in Black/Light Blue wire between PCM and downstream oxygen sensor. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES . The PCM is located between driver's side front fender and power distribution center, near battery.
  8. Ensure ignition is off. Disconnect connectors from Powertrain Control Module (PCM). The PCM is located between driver's side front fender and power distribution center, near battery.
  9. Using ohmmeter, check resistance between terminal No. 4 (Tan/White wire) on wiring harness side of connector for downstream oxygen sensor and PCM connector terminal No. 51 (Tan/White wire). If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit in Tan/White wire between PCM and downstream oxygen sensor. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES .
  10. Reinstall connectors on PCM. Turn ignition on. Connect jumper wire between terminals No. 3 (Black/Light Blue wire) and No. 4 (Tan/White wire) on wiring harness side of connector for downstream oxygen sensor.
  11. Using scan tool, read downstream oxygen sensor voltage. If downstream oxygen sensor voltage is .2 volt or more, replace PCM. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES . If downstream oxygen sensor voltage is less than .2 volt, replace downstream oxygen sensor. Perform TEST VER-5A - ROAD TEST FOR OBD-II TROUBLE CODES .
scientia non olet · About LEMON Manuals