Short answer: Go to the Faults tab in OBDAI. Your codes appear organized into three sections: Stored DTCs, Pending DTCs, and Permanent DTCs. Tap any code for AI-powered insights — causes, severity, and what to do next. To clear codes, pull down on the screen — but read below first.
What Are Diagnostic Trouble Codes?
Diagnostic Trouble Codes (DTCs) are standardized fault identifiers stored by your vehicle’s on-board computer when it detects a problem with an emissions-related system. When certain codes are set, the Malfunction Indicator Lamp (MIL) — your check engine light — illuminates.
DTCs follow a standardized format defined by SAE J1979 and SAE J2012:
- P0xxx — Powertrain (engine, transmission)
- B0xxx — Body (airbags, climate control, lighting)
- C0xxx — Chassis (ABS, stability control, steering)
- U0xxx — Network (communication between control modules)
The first digit after the letter indicates whether the code is generic (0) or manufacturer-specific (1). P0171 is a generic code recognized by any technician worldwide. P1131 may be specific to a particular manufacturer.
How to Scan for Codes
Connect to your vehicle. Ensure OBDAI is connected to your adapter and communicating with your car.
Go to the Faults tab. Bottom navigation bar.
View your codes. OBDAI displays codes organized into three sections:
- Stored DTCs — Confirmed faults currently in memory
- Pending DTCs — Faults detected but not yet confirmed
- Permanent DTCs — Emissions faults that can’t be manually cleared
Tap any code for AI-powered insights from ARIA.
If no codes are stored, the sections will be empty.
Understanding What You See
Tap any code to get ARIA’s analysis. ARIA doesn’t just define the code — it interprets what it means for your specific vehicle based on current sensor data, identifies likely causes, assesses severity, and tells you what to do next.
Each code entry includes:
- Description — What the code indicates
- Likely causes — Common reasons this code appears on your vehicle type
- Severity — Whether you can keep driving or should stop immediately
- Freeze frame data — A snapshot of sensor values at the moment the fault was detected
Freeze frame data is diagnostic gold. It tells you the operating conditions when the fault occurred — engine load, coolant temperature, vehicle speed, fuel trim values. This context helps pinpoint whether the problem happens at idle, under load, during cold start, or at highway speed.
The Three Types of Trouble Codes
OBDAI retrieves three distinct categories of codes, each with different diagnostic significance:
Confirmed Codes (Mode 3)
These are faults that have been validated by the on-board diagnostic system. The vehicle’s computer detected the problem, ran the test again to confirm it wasn’t a fluke, and stored it as a confirmed fault. These codes typically illuminate the check engine light.
When you scan for codes, this is what most people mean — the active, confirmed faults currently stored in memory.
Pending Codes (Mode 7)
Pending codes represent faults detected during the current or most recent drive cycle, but not yet confirmed. Think of them as “under investigation.”
The OBD system detected an anomaly, but hasn’t verified it’s a persistent problem. If the same test fails again on subsequent drive cycles, the pending code becomes a confirmed code and the MIL illuminates. If the system doesn’t see the problem again, the pending code clears automatically.
Why pending codes matter: After a repair, pending codes tell you whether the fix worked before you’ve driven enough to complete all the monitor tests. If the pending code returns after one drive cycle, the repair didn’t solve the problem.
Permanent Codes (Mode A)
Permanent codes are emissions-related faults that cannot be erased by any scan tool, diagnostic service, or battery disconnect. Only the vehicle’s OBD system can remove them — after it verifies the problem is actually fixed through normal driving.
These codes exist specifically to prevent clearing codes right before an emissions inspection. The presence of permanent codes at an inspection — without the MIL illuminated — indicates a proper repair was not verified by the on-board monitoring system.
Permanent codes are stored in non-volatile memory (NVRAM). They persist through battery disconnects and scan tool clears.
How permanent codes clear: The vehicle must complete its monitoring cycle and determine the malfunction is no longer present. For most monitors, this means one or more complete drive cycles with no recurrence of the fault.
How to Clear Codes
From the Faults tab, pull down on the screen to clear codes. OBDAI will send the clear command to all emissions-related control modules.
Clear codes when:
- You’ve completed a repair and want to verify the fix
- The code was caused by a one-time event (loose gas cap, contaminated fuel, temporary sensor glitch)
- You need to reset the check engine light after confirming the repair
Don’t clear codes when:
- You haven’t diagnosed the problem yet — clearing erases freeze frame data and diagnostic history
- You’re about to take an emissions test — clearing resets all readiness monitors
- You want to see if a problem recurs — the code is your evidence
Clearing codes doesn’t fix anything. It erases the record. If the underlying problem still exists, the code will return — usually within one to three drive cycles.
What Clearing Actually Does
When you pull down to clear codes, the vehicle’s OBD system resets the following per SAE J1979:
- Malfunction Indicator Lamp (turns off)
- Confirmed diagnostic trouble codes
- Pending diagnostic trouble codes
- Freeze frame data
- Oxygen sensor test data
- On-board monitoring test results
- I/M readiness status (all monitors reset to “not complete”)
- Distance traveled while MIL active
- Distance traveled since codes cleared
- Engine run time while MIL active
- Warm-up cycles since codes cleared
The readiness reset is critical. Most emissions testing programs require all monitors (or all but one or two) to show “Ready” status. Clearing codes resets them to “Not Ready.” You’ll need to complete a drive cycle — sometimes several — before the vehicle is testable again.
See our emissions readiness article for drive cycle requirements.
Permanent Codes Can’t Be Cleared
If you see codes that won’t clear, they’re likely permanent codes. This isn’t a bug in OBDAI — it’s the OBD system working as designed.
Permanent codes clear only when:
- The diagnostic monitor for that fault runs to completion
- The test passes (malfunction no longer detected)
- The vehicle meets the regulatory drive cycle requirements
For monitors subject to in-use ratio requirements, the system must execute the minimum number of checks necessary and determine no malfunction exists. For other monitors, a complete drive cycle with no recurrence typically clears the permanent code.
Hardware Required
Reading and clearing trouble codes requires an OBD-II adapter connected to your vehicle. OBDAI hardware provides reliable connections across all platforms.
Related Articles
- Getting Started with OBDAI
- Understanding Emissions Readiness (coming soon)
- What OBDAI Can and Cannot Diagnose (coming soon)
Questions? support@obdai.app