1

('07 Cobalt LS, 2.2L Ecotec)

In this car's 'mode 6' OBD2 data, there is a GM-defined item, "Post Catalyst Sensor Open Test" (Test ID 8A). This page shows it as a count. My scan tool also shows it having an accompanying "Maximum" (480). Whenever the count exceeds this Max, the test is marked as "Failed"; otherwise, it can be "Pass", or (occasionally) "Incomplete". The count seems to be reset to 0 at startup.

Over ~150 trips I've looked at, this count has ranged from 0 to 800. If over 480, it's flagged as "Failed". I have replace the sensor in question, to no effect.

Anyway, questions

  • What triggers the count? Is it literally an "open" circuit, loss of continuity?
  • Is it testing the O2 sensor's heater, or the sensor itself?
  • What interval are the counts accumulated over?
  • Can a "failed" status lead to a CEL/MIL? (I've had no CEL codes explicitly indicating an Oxygen Sensor failure.)
  • Can a "failed" status = without a CEL - prevent the EVAP test from running?
Improve this question

1 Answer 1

Reset to default
0

Open generally means that the circuit is open, so a loss of continuity. If you have replaced the sensor then it's probably an electrical problem in the wiring. It could be a problem in the ECU itself but it's more likely something in the connector or the wiring loom. I'd start by checking the connector for faults and giving it a good clean, then work your way up to see if there's chafing or some other visible problem.

Open heater circuits do have a separate diagnostic code (P0135), whether GM uses that code or lumps continuity together with the sensor I don't know. I'd assume they don't for now. The troubleshooting is the same process anyhow.

Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .