OBD II Test Driving

Planning Your Test Drive
Few repairs to an OBD II system will be complete without a test drive. Virtually every diagnostic procedure is built around the fact that, no matter how good your equipment, only the car's ECM can really tell if the problem is fixed. Because of the extensive enabling criteria for most diagnostics, it will be necessary to drive the car to give the ECM a chance to check for codes and verify your repair.

Each test in the enhanced shop manual will give you a driving cycle which will run the diagnostic in the least possible time. ALWAYS follow the drive cycle for the particular fault(s) you have been repairing.

When driving, keep in mind that there are many variables affecting the time needed for the diagnostic to run. All of the following factors will increase the time a test takes to run.

1 Traffic conditions. Having to brake or change speed substantially will cause some tests to abort and restart.
2 Driving style. Any abrupt changes in engine load will increase the time it takes to run some tests.
3 Engine variant. Some fuel systems take longer than others to run the same test.
4 The type and number of faults. A fault in one system may prevent the diagnostic for another system from running.
5 Climate. Many of these tests are affected by changes in engine load. A hot day where the A/C and cooling fan are cycling can lengthen the test considerably.
6 Combine several of the above and you increase the time even more.