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DTC 211: Co Potentiometer

  1. 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 10). If fault is intermittent and signal is too high, go to step 12). If fault is intermittent and signal is too low, go to step 13).
  2. Turn ignition off. Disconnect CO potentiometer connector. Turn ignition on. Connect voltmeter between CO potentiometer connector terminal No. 3 and ground. If about 5 volts are present, go to next step. If less than 5 volts are present, go to step 7). If greater than 5 volts are present, note that CO potentiometer power lead is connected to A/C pressure sensor power lead inside ECM. If any problem is present in either lead both components will be affected. Check for a short circuit to voltage in wiring between CO potentiometer connector terminal No. 3 and ECM connector terminal B1, and between A/C pressure sensor terminal No. 3 and ECM connector terminal B29.
  3. Ensure ignition is off and CO potentiometer is disconnected. Connect ohmmeter between CO potentiometer connector terminal No. 1 and ground. If ohmmeter reads about zero ohms, go to next step. If ohmmeter does not read about zero ohms, check ECM connector for poor terminal contact. Repair as necessary. If terminal contact is okay, connect ohmmeter between CO potentiometer connector terminal No. 1 and ground. If ohmmeter reads about zero ohms, cause of DTC was poor terminal contact at ECM connector. If ohmmeter does not read about zero ohms, check for an open circuit in wiring between CO potentiometer terminal No. 1 and ECM terminal B28. Repair as necessary.
  4. Ensure ignition is on and CO potentiometer is disconnected. Connect voltmeter between CO potentiometer connector terminal No. 2 and ground. If about 5 volts are present, go to step 6). If less than 5 volts are present, go to next step. If greater than 5 volts are present, check for short circuit to voltage in wiring between CO potentiometer terminal No. 2 and ECM connector terminal B32. Repair as necessary.
  5. Ensure ignition is off and CO potentiometer is disconnected. Check ECM connector for contact resistance. Repair as necessary. Reconnect ECM connector. Turn ignition on. Connect voltmeter between CO potentiometer connector terminal No. 2 and ground. If about 5 volts are present, DTC was caused by poor ECM terminal contact. If about 5 volts are not present, check for an open circuit in wiring between CO potentiometer terminal No. 2 and ECM connector terminal B32.
  6. Ensure CO potentiometer is disconnected. Remove seal from CO potentiometer plug hole. Drill 2 .079 (2 mm) holes in plug. Pull out plug. Reconnect CO potentiometer connector. Start and idle engine. Using scan tool, read CO potentiometer value. Turn adjustment screw clockwise to lower voltage. If reading is okay, adjust CO. See ADJUSTMENTS article. If reading is not okay, replace CO potentiometer.
  7. Ensure ignition is off and CO potentiometer is disconnected. Wait about 2 minutes. Connect ohmmeter between CO potentiometer connector terminal No. 3 and ground. If ohmmeter does not read about zero ohms, go to step 9). If ohmmeter reads about zero ohms, go to next step.
  8. Ensure ignition is off and CO potentiometer is disconnected. Disconnect A/C pressure sensor. Connect ohmmeter between CO potentiometer connector terminal No. 3 and ground. If ohmmeter reads .2-1.5 k/ohms, replace A/C pressure sensor. If ohmmeter does not read .2-1.5 k/ohms, ensure CO potentiometer is connected to A/Cpressure sensor power lead in ECM. If a problem is present in either power lead, both components will be affected. Check for short circuit to voltage in wiring between CO potentiometer terminal No. 3 and ECM terminal B1, and A/C pressure sensor terminal No. 3 and ECM terminal B29. Repair as necessary.
  9. Ensure ignition is off and CO potentiometer is disconnected. Check ECM connector terminals for poor terminal contact and repair as necessary. Reconnect ECM connector. Connect ohmmeter between CO potentiometer connector terminal No. 3 and ground. If ohmmeter reads about .2-1.5 k/ohms, DTC was caused by poor terminal contact. If ohmmeter does not read about .2-1.5 k/ohms, check for open circuit in wiring between CO potentiometer terminal No. 3 and ECM connector terminal B1. Repair as necessary.
  10. If fault is permanent and signal is too low, turn ignition off. Disconnect CO potentiometer. Turn ignition on. Connect voltmeter between CO potentiometer connector terminal No. 2 and ground. If voltmeter reads 5 volts, go to next step. If voltmeter does not read 5 volts, check for short circuit to ground in wiring between CO potentiometer terminal No. 2 and ECM connector terminal B32.
  11. Ensure CO potentiometer is disconnected. Remove seal from CO potentiometer plug hole. Drill 2 .079 (2 mm) holes in plug. Pull out plug. Reconnect CO potentiometer connector. Start and idle engine. Using scan tool, read off CO potentiometer value. Turn adjustment screw counter-clockwise to increase voltage. If reading is okay, adjust CO. See ADJUSTMENTS article. If reading is not okay, replace CO potentiometer.
  12. If fault is intermittent and signal is too high, check CO potentiometer and ECM connectors for poor terminal contact. Also, check for an intermittent open circuit in wiring between CO potentiometer terminal No. 3 and ECM connector terminal B1, and between CO potentiometer terminal No. 1 and ECM connector terminal B28. Check for intermittent open circuit or short circuit to voltage in wiring between CO potentiometer terminal No. 2 and ECM connector terminal B32. Since CO potentiometer power lead is connected to A/C pressure sensor power lead inside ECM, also check for short circuit to ground or voltage in wiring between CO potentiometer terminal No. 3 and ECM connector terminal B1, and between A/C pressure sensor terminal No. 3 and ECM connector terminal B29. Repair as necessary.
  13. If fault is intermittent and signal is too low, check for an intermittent short circuit to ground in wiring between CO potentiometer terminal No. 2 and ECM connector terminal B32. Repair as necessary.
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