Diagnostic Aids

WARNING: This page is about a different car, the 2017 Chevrolet Spark. However, it is still accessible from the selected car via links, so may be relevant.

For symptom byte 21 the module only runs diagnostic when the vehicle is driven greater than 40 km/h (25 MPH). Therefore, even with clean sensor with no obstruction (i.e snow or ice melted off) drive the vehicle greater than 40 km/h (25 MPH).

The following is a list of reasons this failure type byte 21 might have set:

One or more of the sensors may be blocked by snow, mud, ice or debris. This might happen after going through a car wash in cold weather.
Silicone insulator surrounding sensor maybe missing, cut or twisted.
Improperly installed sensor, sensor maybe be crooked due to a tight wire harness.
One or more of the sensors may be scratched or the paint maybe chipped.
Excessive paint thickness on a sensor may cause an excessive sensor ring time. When replacing or refinishing a sensor, do not apply an excessive amount of paint or clear coat.