Lauren HollandBy Lauren Holland

Updated November 2026

An OBD2 scanner that clears codes lets you erase trouble codes and turn off the check engine light without a shop visit. That feature is useful after you have fixed a problem, but it can also hide a fault that is still active. This guide explains how to read codes first, when clearing makes sense, and how to do it without losing information you may need later.

Read the Codes Before You Clear Anything

Clearing a code deletes the stored fault data, including the freeze frame, which records engine speed, coolant temperature, and fuel trim at the moment the fault set. Always record the codes and freeze frame data first. Write down each code, its status (pending, confirmed, or permanent), and the mileage.

Shopping for one? See our guide: 3 Best OBD2 Scanners for Nissan Rogue Compared (2026).

Look up each code in a reliable source such as the manufacturer’s service information or a generic OBD2 code list. A P0301 means cylinder 1 misfire, while P0420 points to catalyst efficiency below threshold. Knowing what the code means tells you whether the problem is likely fixed.

Decide Whether Clearing Is Appropriate

Clear codes only after you have repaired the cause, or when you need to confirm a fix. If you clear a code and the light stays off, the problem may be intermittent or not yet re-tested by the car’s self-check routines.

Many emissions monitors need a set number of drive cycles to complete. After clearing, the readiness monitors show “not ready.” Drive the car through a mixed cycle of city and highway driving, typically over several days, before expecting the monitors to report complete.

Step-by-Step: Clearing Codes With a Scanner

  1. Turn the ignition to the on position with the engine off.
  2. Plug the scanner into the OBD2 port, usually under the dash on the driver’s side.
  3. Read and record all stored and pending codes, along with freeze frame data.
  4. Repair the fault, then select the clear or erase codes function.
  5. Confirm the light is off and check readiness monitor status.
  6. Start the engine and drive through a varied route to let the monitors run.

Checking Readiness Monitors

Most scanners show a readiness screen with each monitor marked complete or incomplete. Catalyst, EVAP, and oxygen sensor monitors are the usual ones that take the longest. An incomplete monitor is normal right after clearing and does not mean the repair failed.

Situation Action
Fault repaired, code confirmed fixed Clear and verify readiness
Fault not yet diagnosed Record codes, do not clear
Intermittent code returns quickly Keep the record and investigate further
Before an emissions inspection Avoid clearing; monitors must be complete

A scanner with live data and freeze frame display makes it easier to record codes before clearing. Look for a model that shows readiness monitor status clearly so you know when the car has finished its self-tests. View on Amazon

A small OBD2 extension cable can help when the port is hard to reach behind a steering column or in a tight footwell. View on Amazon

Common Mistakes and Tips

  • Clearing codes before writing them down, which erases the freeze frame data.
  • Assuming the light staying off means the problem is solved.
  • Clearing codes right before an emissions test, which will likely fail on incomplete monitors.
  • Ignoring flashing check engine lights, which can signal an active misfire that needs immediate attention.
  • Skipping a drive cycle after clearing, which leaves the car unable to confirm the repair.

For related model-specific steps, see OBD2 Scanner for Honda Civic: How to Read and Clear Codes at Home or OBD2 Scanner for Ford: How to Read and Clear Codes at Home. If you own a diesel, OBD2 Scanner for Diesel: How to Read and Clear Codes on Your Diesel Engine covers the differences in codes and readiness behavior.

FAQ

Will clearing codes fix the problem?

No. Clearing only deletes the stored information and turns off the light. The underlying fault will set the code again if it is still present.

Does clearing codes reset my car’s computer?

Clearing codes resets the fault memory and readiness monitors but does not erase learned settings like idle or fuel trims, which the engine control module relearns over time.

How long should I wait before checking the readiness monitors?

Wait for several normal drive cycles, usually a few days of mixed driving. Some monitors need specific conditions, so check your vehicle’s service information for exact requirements.

Conclusion

An OBD2 scanner that clears codes is most useful after a confirmed repair. Always record codes and freeze frame data first, then clear only when the cause is fixed. Give the car time to complete its readiness monitors before judging the result. For guidance on serious or repeated faults, consult a qualified mechanic.

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Lauren Holland

About Lauren Holland

Lauren Holland is part of our editorial team and reviews and edits our car care & garage supplies guides, checking product details against manufacturer specifications and owner feedback.