A genuine permanent emissions code, or PDTC, cannot be removed on a reader’s command. The vehicle must verify that the fault is gone. Keep dated reports, avoid repeated resets and investigate symptoms or codes that return.
Permanent describes stored information, not an everlasting fault
California’s public Bureau of Automotive Repair (BAR) explains that a PDTC cannot be erased with a scan-tool clearing command or by disconnecting the battery. The vehicle’s OBD system removes it after verifying that the previously detected problem is no longer present. This is why a code number can remain visible after a repair.
Terminology matters. Some tools use permanent to mean a fault that is currently present, rather than a PDTC entry. Before drawing conclusions, capture the complete status label, control unit and description. A code number copied on its own does not resolve that ambiguity.
This guide concerns permanent emissions diagnostic trouble codes, not every fault labelled permanent by a manufacturer-specific diagnostic tool.
What to record before touching the clear button
Create a simple follow-up record: model, year, fuel type, mileage, repair date and invoice or workshop report. Add the exact code and status, related codes and check-engine light state. Save freeze-frame and readiness information only where the vehicle and application provide it.
A dated post-repair reading is more useful than a sequence of screenshots taken after resets. If the workshop has already cleared the codes, record that fact. The aim is an honest before-and-after comparison, not an artificially empty screen.
- Is the code listed only as permanent or in another category as well?
- Is the warning light actually off with the engine running?
- Have the original symptoms disappeared or returned?
- Which self-tests remain incomplete, if that information is available?
When to follow up and when to return to the workshop
If the repair is documented, symptoms are absent and only the permanent entry remains, ask the repairer how completion of the relevant self-tests can be confirmed on this vehicle. That entry alone does not justify replacing the same part again. Equally, it does not guarantee that everything is resolved.
If the warning light returns, the same fault appears outside the permanent-code category, or symptoms recur, further diagnosis is needed. Give the workshop your reports so it can review the original repair, other faults and the conditions under which checks run.
Do not drive solely to clear a code when the vehicle has major power loss, stalling, overheating or a flashing warning light. Stop safely, consult the handbook and obtain appropriate assistance. A displayed code status never grants permission to drive.
Why there is no universal distance to drive
BAR explains that self-tests depend on operating conditions such as temperature, load and speed. Some journeys never provide the necessary conditions. Another defective component can also prevent completion. Driving a long way is not the same as completing the relevant test.
Do not copy a drive cycle intended for another engine. This guide prescribes no engine speed, motorway journey or number of starts. Manufacturer procedures must match the exact vehicle and be safe to perform. Repeated resets obscure the record; disconnecting the battery is not a PDTC solution.
Documented exceptions do not automatically apply to your car
Sources last checked: 19 September 2026. Section E of BAR’s reference lists known difficulties removing certain PDTCs. These examples explain why a vehicle-specific review may be needed. They do not mean a fuel-system fault can be ignored.
| Vehicle and fuel | Model year | Permanent codes listed by BAR | Evidence and limit |
|---|---|---|---|
| Audi Q7, 3.0 TDI diesel | 2010 | P0087, P0088, P053F | BAR section E: documented clearing issue, not an OBDPhone® test. |
| Audi Q7, 3.0 TDI diesel | 2011–2012 | P0087, P0088, P053F, P064A, P2635, P0230 | BAR section E: the list changes with model year; do not generalise to European Q7s. |
| Volkswagen Touareg, 3.0 TDI diesel | 2010 | P20B5, P0087, P0088, P053F | BAR section E: California inspection scope, not a universal repair instruction. |
Evidence level: public-agency documentation, not an OBDPhone® database observation or exact-engine test. No failure rate or product compatibility is inferred. Any intervention requires confirmation for the relevant market and VIN.
Inspections and used-car buying: separate the evidence
The cited reference concerns California’s Smog Check. Its thresholds and exceptions are not the rules for an MOT or for French or Belgian inspections. This guide therefore does not predict a local pass or fail from a PDTC alone. Ask the relevant inspection provider what applies to your vehicle.
When buying a used car, a permanent code prompts practical questions: what fault was repaired, when, and what records support that? Conversely, a code-free scan is not a clean bill of health. Combine the scan with service history, a mechanical inspection and repair evidence. The related guides explain responsible clearing, engine-code interpretation and the differences between generic OBD2 and manufacturer diagnostics.
OBDPhone® capabilities — no forced-clearing promise
On a compatible vehicle, OBDPhone® reads generic engine and emissions fault codes and available engine data. Clearable codes may be cleared only after repair. Status details, freeze-frame and readiness access depend on the vehicle and application; no particular display is guaranteed.
OBDPhone® cannot force a PDTC to disappear and does not guarantee ABS, airbags, traction-battery access, coding, programming or manufacturer functions. Use the compatibility checker before buying and the product page for the exact scope. For a reading question, contact support@obdphone.com with model, year, fuel type and a status screenshot, hiding personal information.
Frequently asked questions
The essential answers.
Why does a code remain after repair?+
For a genuine PDTC, the vehicle must verify that the fault has gone before removing the entry. Its presence alone does not prove the repair failed.
Can another scanner or a disconnected battery clear it?+
Not a genuine permanent emissions PDTC. Do not confuse that memory with an active fault labelled permanent by a tool.
How far must I drive?+
No universal distance is guaranteed. Test conditions and unresolved faults matter more than an arbitrary mileage.
Does an extinguished light guarantee an inspection pass?+
No. It is not a certificate of compliance. Local inspection requirements and the vehicle’s overall condition still matter.
This guide supports an initial understanding. It does not replace the vehicle manual, manufacturer safety instructions or an assessment by a qualified professional.
Primary sources
Reviewed to verify the facts and show why procedures depend on the vehicle.