Are you struggling to get your 1999 Toyota Corolla’s OBD2 readiness tests to complete, specifically the Catalyst and Oxygen Sensor tests? You’re not alone, and there might be a surprisingly simple explanation. Many Toyota owners face frustration when one of these tests stubbornly refuses to run while the other completes without issue. If this sounds familiar, the problem could stem from an unexpected source: a possible error in your Toyota repair manual.
It appears that the instructions for the Oxygen Sensor and Catalyst readiness tests in certain Toyota manuals, potentially including those relevant to the 1999 Toyota Corolla and similar models using OBD2 systems, might be reversed. According to user experiences and observations, following the steps outlined for the Oxygen Sensor test may actually trigger the Catalyst test, and vice versa.
This means if you’re trying to run the Catalyst test and it’s not cooperating, you should try performing the steps detailed for the Oxygen sensor test in your manual. Conversely, if the Oxygen sensor test is proving elusive, attempt the procedure described for the Catalyst test.
Based on anecdotal evidence, here’s a breakdown of the potentially reversed procedures:
If you can’t get the Catalyst test to run (try the Oxygen Sensor test procedure from the manual):
- Idle your 1999 Toyota Corolla for 2 minutes.
- Repeat the following sequence 10 times:
- Drive above 25 mph (approximately 40 km/h) for 50 seconds.
- Idle for 40 seconds.
If you can’t get the Oxygen test to run (try the Catalyst test procedure from the manual):
- Drive your 1999 Toyota Corolla between 40 to 55 mph (approximately 64 to 88 km/h) for 3 minutes.
- Then, drive between 35 to 45 mph (approximately 56 to 72 km/h) for 7 minutes.
It’s important to emphasize that this observation is based on user experience and isn’t an official Toyota service bulletin. Therefore, we cannot guarantee this reversal is true for every 1999 Toyota Corolla or every Toyota vehicle using these readiness tests. However, for owners struggling with these specific OBD2 monitors, especially on older Toyota models around the 1999 Corolla era, this could be a valuable troubleshooting step.
One Toyota owner with a 2008 Matrix discovered this discrepancy after extensive troubleshooting. They noticed a pattern where attempting the Oxygen Sensor test steps consistently triggered the Catalyst test instead. By using an OBD2 reader to monitor and reset the readiness tests, they confirmed this reversed behavior through repeated trials and detailed observations. This allowed them to successfully run the Oxygen sensor test independently when needed, simply by using the Catalyst test procedure from the manual.
Why would someone want to run the Oxygen Sensor test separately? In some cases, like the Matrix owner’s experience, a vehicle might have a minor, unresolved issue that triggers a check engine light specifically when the Catalyst test runs, even if the car passes emissions standards. In locations with vehicle inspections requiring both readiness tests to be completed and the check engine light to be off, this reversed procedure could offer a workaround to pass inspection by ensuring the Catalyst test doesn’t run before the inspection. This involves completing all drive cycles except the Oxygen sensor test (using the Catalyst test procedure), getting the inspection, and then allowing the Catalyst test to run (by performing the Oxygen sensor test procedure) after passing inspection, even if it triggers the check engine light later.
Disclaimer: Employing such workarounds for inspection purposes should not be interpreted as a solution for neglecting vehicle maintenance or emissions-related problems. It is crucial to address any underlying issues affecting your vehicle’s emissions system. However, for owners facing similar frustrating situations with OBD2 readiness tests on their 1999 Toyota Corolla or comparable models, understanding this potential manual error could provide a path to resolve their immediate inspection concerns and further diagnose their vehicle’s OBD2 system behavior. Always consult with a qualified mechanic for proper diagnosis and repair of any vehicle issues.
