Clearing codes

Clearing codes is one tap, which is exactly the problem. It is worth thirty seconds of reading first.

How to do it

Two routes, same result. On the Codes tab there is a red Clear codes button at the foot of the list, and the same command sits in the overflow menu at the top. When there is nothing to clear, the menu item is greyed out and reads No codes to clear.

Either way a dialog appears, titled Clear trouble codes?, and it tells you plainly that this erases stored codes and resets the emissions readiness monitors, that it will not fix the underlying problem, and that if the fault is still present the code will return.

If permanent codes are stored, the dialog says how many will remain.

Confirm and you get Codes cleared, or Couldn't clear codes if the car refused.

What clearing does

It erases stored and pending trouble codes, turns the check engine light off, throws away the freeze frame, and resets every emissions readiness monitor to not ready.

That is all it does. It is a memory wipe, not a repair.

What clearing does not do

It does not fix anything. If the fault is still there, the computer finds it again, usually within a drive or two, and the light comes back. Clearing a code to make a light go away is borrowing against a few days.

It does not remove permanent codes. Only the vehicle can clear those, after it has re-run the relevant monitor and confirmed the repair itself.

The emissions trap

This is the one that catches people, so it gets its own section.

Clearing codes resets your readiness monitors. An emissions test checks three things: that the light is off, that no codes are stored, and that the monitors have run. Clearing takes care of the first two and destroys the third.

So the day before an inspection is the worst possible time to clear codes. You will arrive with a car that looks perfect on the dashboard and fails on the third check, and the monitors take a mix of driving to reset, commonly somewhere between 50 and 100 miles including both highway and stop-and-go.

Check readiness before you drive to the station, not at it. Chapter eight is how. The readiness guide has the longer version.

When clearing is the right move

After a repair, to confirm the fix. Clear the code, drive the car normally, and see whether it comes back. That is a real test and it is the reason the feature exists.

To clear a code you have already diagnosed and dealt with, like a P0442 from a gas cap you have now tightened.

Before selling a car, no. The permanent code stays, the monitors read not ready, and any buyer with a twenty dollar adapter can see exactly what happened.

What to do next

Chapter eight is readiness monitors: what they are, and how to get them to run.