Mode Ten permanent codes are the answers a vehicle gives when a scan tool sends the standard OBD-II request known as Service $0A, which asks for emissions faults stored in protected memory. It is the last of the ten generic diagnostic services, added later than the others, and the one many owners have never opened on their scan tool.
This article explains the service from the tool side: how to request it, what the response looks like, why some vehicles and readers do not support it, and how to interpret the results alongside other modes. For the concept behind permanent codes and the steps to resolve one, see the related guides on this site.
The Last Service on the OBD-II Menu
OBD-II scan tools communicate using standardized services, numbered $01 through $0A in hexadecimal, which is why the tenth service is written as $0A. Each service requests a specific type of information, such as live data, freeze frame snapshots, stored codes or vehicle identification details.
Service $0A was added to address a weakness in the original design. Clearing codes through Service $04 erased stored emissions faults completely, so a vehicle could appear fault-free shortly after an unresolved problem was wiped from memory.
Mode 10 reads a separate record that Service $04 cannot touch. When the vehicle supports it, the result shows emissions-related faults that were confirmed and are still waiting for the vehicle to verify a repair through its own monitors.
Which Vehicles Answer a Mode Ten Request
Permanent code support was phased in on newer vehicles, so not every OBD-II car responds to Mode 10. An older vehicle may answer that the service is not supported, or the tool may simply return no data. Neither result indicates a fault with the car or the scan tool.
If you are unsure whether your vehicle supports the service, the owner’s manual, service information or your state emissions program can help. Some inspection programs publish which model years they check for permanent codes during plug-in testing.
Support also depends on the module. On vehicles with separate engine and transmission computers, each emissions-related module may keep its own permanent code memory. A good scan tool shows which module reported any permanent code it finds.
Requesting Mode Ten on a Scan Tool
Many recent generic readers include a permanent code option, though it may be hidden in a submenu. Older or very basic tools sometimes lack it entirely. The process is similar to reading other code types.
- Park the vehicle, set the parking brake and place the transmission in park or neutral.
- Connect the tool to the 16-pin diagnostic connector, usually under the driver’s side of the dashboard.
- Turn the ignition on, or start the engine outdoors or in a ventilated area if the tool requires it.
- Open the codes menu and select permanent codes, Mode 10 or Service $0A.
- Record any codes shown, the reporting module and the date and mileage.
If the menu offers no permanent code option, check the tool’s manual or update its software. Some tools display permanent codes automatically within a combined code report, marked with a separate status.
Interpreting What Mode Ten Returns
A Mode 10 response is simple, but each possible result means something slightly different. Read it together with other services rather than on its own.
One or More Permanent Codes
A listed code, such as P0420 for catalyst efficiency below threshold on bank 1, means the fault was confirmed and the vehicle has not yet verified a repair.
Compare it with Mode 3 stored codes and the check engine light. If the stored code is also present and the lamp is on, the fault is still active. If only the permanent code remains, the related monitor probably has not yet completed a passing run since the last clear or repair.
No Permanent Codes
An empty result means no protected emissions faults are waiting for verification. It does not mean every system is healthy.
Check Mode 7 for pending codes and Mode 1 readiness status. Incomplete monitors may still be hiding a fault that has not been detected yet, especially soon after codes were cleared or the battery was disconnected.
Service Not Supported
This response means the vehicle or module does not implement Mode 10. Rely on stored codes, pending codes and readiness status instead, and confirm local inspection requirements with your state program.
It is common on vehicles built before permanent code support was phased in. Make sure the tool has communicated with the correct module before assuming the vehicle lacks the service.
Why Mode Four Leaves Mode Ten Untouched
Service $04, commonly called Mode 4, clears stored and pending codes, erases freeze frame data and resets readiness monitors to not ready. It is the standard way to reset diagnostic memory after a repair, and every generic scan tool includes it.
Permanent codes are intentionally excluded from that reset. Disconnecting the battery has the same limitation on vehicles designed to the requirement. The only legitimate way to clear a permanent code is for the related monitor to run and pass, showing that the fault is no longer present.
This design is why a Mode 10 check after clearing codes can look confusing. Mode 3 shows nothing, the lamp is off, yet Mode 10 still lists the fault. That combination is expected and simply means the vehicle is still waiting for proof of the repair.
How Inspection Stations Use Mode Ten
In states that use plug-in OBD inspections, the testing equipment reads codes, readiness status and, on supported vehicles, permanent codes. A permanent code can lead to a failed or rejected test in some programs, even when the check engine light is off.
Requirements vary by state, including the model years tested and how permanent codes are handled. The state emissions program website or a licensed inspection station is the correct source for current rules. Do not rely on general advice for your specific test.
Running your own Mode 10 check before an inspection is a useful habit. If a permanent code is present, you gain time to diagnose the fault and complete the monitors through normal driving instead of discovering the problem at the testing lane.
Common Mode Ten Misunderstandings
Because Mode 10 behaves differently from the other code services, it is often misread. These misunderstandings come up frequently among DIYers.
- Believing a permanent code means the fault can never be removed; it clears once the monitor passes.
- Assuming the scan tool is faulty because Mode 4 does not erase Mode 10 results.
- Thinking an empty Mode 10 list proves the car will pass inspection without checking readiness.
- Replacing a part again because a permanent code remains, before giving the monitor time to run.
Each of these leads to unnecessary expense or frustration. Reading Mode 10 alongside Mode 1, Mode 3 and Mode 7 avoids most of them and shows whether the issue is an active fault or simply a monitor that still needs to complete.
Mode Ten in a Complete Code Check
A thorough generic scan uses several services in a logical order. Start with Mode 1 to check readiness status and the lamp command. Then read Mode 3 stored codes, Mode 7 pending codes and Mode 10 permanent codes, and review Mode 2 freeze frame data for any stored fault.
This sequence shows the full life cycle of emissions faults. Pending codes reveal what was just detected, stored codes show what was confirmed, and permanent codes show what is still unverified. Readiness status tells you which monitors have had a chance to report.
Record all results before clearing anything. Once Mode 4 is used, most of this information is gone, while the permanent code remains as the only reminder. A full record keeps diagnosis grounded in evidence.
Safety and Good Practice During Mode Ten Checks
Reading permanent codes is a stationary task. Perform it with the vehicle parked and the parking brake set. If the engine must run, keep the vehicle outdoors or in a well-ventilated area and keep cables away from moving belts and the cooling fan.
Never interact with the scan tool while driving. If you need to drive to let a monitor complete, recheck Mode 10 after you park. A passenger can watch live data on a road test when that is truly needed.
Avoid any product or method that claims to erase permanent codes or reprogram emissions systems. Tampering with emissions controls can violate federal and state rules and may cause inspection failure. A real repair followed by normal driving is the only reliable path.
Making Mode Ten a Routine Check
Mode Ten permanent codes add a valuable layer of information to every scan on supported vehicles. They show what the car still considers unresolved, even when the lamp is off and stored codes are gone.
Make the Mode 10 check part of your standard routine, especially after repairs and in the weeks before an inspection. Note results in your maintenance log so you can see when a permanent code appears and when it clears.
If a permanent code stays after you have repaired the cause and driven under normal conditions, consult the service manual or a qualified technician. The code is not an obstacle to fight but a reliable reminder that the vehicle still needs proof that the fault is truly fixed.