Short answer: OBDAI reads your vehicle’s diagnostic evidence so ARIA can explain what it means together: trouble codes, readiness, Mode 6 test results, freeze frames, live readings, vehicle information, counters, and recorded history. Ask what needs attention, what changed since the last drive, or what still needs checking before an emissions test.
OBDAI’s classic OBD data catalog contains 220 Service 01 parameter definitions. OBDAI 2.7 PRO also supports SAE J1979-2 / OBDonUDS, with the GEN2 adapter, on vehicles that use it. Those are decoding capabilities; the vehicle, responding modules, protocol, adapter, selected readings, and plan determine the evidence available in your session.
For that newer-vehicle workflow, explore OBDAI PRO + GEN2 and check compatibility. The sections below explain what ARIA can use and where the limits are.
Start with the question. Let ARIA connect the evidence.
“Is this a developing problem, a recently cleared fault, or a test that has not run?” A code list or a green readiness label alone cannot answer that. ARIA can combine the current session with available monitor tests, fault snapshots, operating conditions, and earlier sessions to explain what supports a conclusion and what remains uncertain.
- Ask for the whole picture. Connect, collect the relevant data, and ask ARIA to explain the codes and readiness alongside the live readings. Evidence from all responding emissions-related modules matters; one module’s clean result need not describe the whole vehicle.
- Investigate the reason. ARIA can retrieve a fault’s freeze frame, inspect the ECU’s Mode 6 measurements and limits, and use warm-up, distance, time-since-clear, and in-use counters to assess how much testing has occurred.
- Compare after the next drive or repair. Where saved sessions are available, ask what changed. ARIA can compare the same monitor test across drives and review recorded sensor behavior, rather than treating each scan as an isolated code list.
Choose the setup for your vehicle
For the OBDonUDS workflow below, choose OBDAI PRO with GEN2. PRO also lets you continue ARIA conversations in the web dashboard. Classic OBD features remain available according to your plan; PRO is not required just to read classic readiness. Premium includes saved history and browser viewing; interactive web ARIA requires PRO.
Explore OBDAI PRO + GEN2 · Check vehicle and adapter compatibility · Compare Premium and PRO
OBDonUDS: newer protocol, the same ARIA workflow
Classic OBD uses diagnostic services such as Mode 01 for current data and Mode 09 for vehicle information. SAE J1979-2 carries standardized emissions diagnostics over UDS (Unified Diagnostic Services). It is a different way to request the evidence, not simply a longer classic PID list. A vehicle using OBDonUDS may not answer a classic-only scanner’s requests.
OBDAI 2.7’s OBDonUDS beta detects the protocol and brings the supported evidence into ARIA’s diagnostic workflow. It requires PRO and the OBDAI GEN2 adapter; GEN1 and a generic ELM327 adapter do not qualify for this feature. Support is vehicle-specific, not a promise that every vehicle of a particular model year implements the same data.
| Evidence available where supported | What ARIA can do with it |
|---|---|
| Stored, pending, and permanent faults from responding modules | Relate fault status and module identity to the rest of the session. |
| Readiness by monitor group and associated fault status | Explain which groups have completed and where the reported evidence conflicts or remains incomplete. |
| DTC snapshots / freeze frames | Examine decoded operating conditions associated with a particular fault. |
| Extended fault records | Interpret reported test results, activity, operating time, and in-use monitoring counts. A monitor completion count is not a count of fault occurrences. |
| Live data and vehicle information | Keep the diagnosis grounded in the responding vehicle’s identity and actual readings. |
| Monitor-test results through the OBDonUDS bridge | Use supported F6xx test results in the Mode 6 workflow, including measured values and ECU limits. |
Technically, OBDAI reads supported $22 F4xx live-data, F6xx monitor-test, and F8xx vehicle-information records, plus $19 fault services, including readiness groups, snapshots, and extended records. These paths have been exercised in implementation testing; a particular vehicle may return only part of them.
OBDonUDS support does not mean unrestricted manufacturer diagnostics, coding, programming, actuator control, or access to every ABS, airbag, body, or battery-management function. Read why newer vehicles need OBDonUDS and OBDAI’s diagnostic boundaries before choosing a setup.
Classic OBD Modes / Services 01–0A: capability map
“Mode” and “Service” are commonly used for the same classic OBD request. The numbers below are hexadecimal. A service existing in the standard does not mean OBDAI exposes it as a feature.
| Mode | Purpose | OBDAI capability and useful boundary |
|---|---|---|
| 01 | Current data and diagnostic status | Reads supported live parameters, readiness, MIL status, and operating counters. The catalog count is explained below. |
| 02 | Freeze-frame data | Reads supported stored sensor snapshots so ARIA can examine conditions associated with a fault; not continuous video-like recording of the event. |
| 03 | Stored emissions-related DTCs | Reads codes from responding modules; ARIA relates them to other evidence rather than treating a code as a parts-replacement instruction. |
| 04 | Clear/reset emissions diagnostic information | User-initiated code clearing. It can erase useful fault evidence and reset readiness; it does not repair a fault or erase permanent codes. |
| 05 | Legacy oxygen-sensor monitoring tests | No dedicated Mode 05 workflow is exposed. Do not interpret the service name in the standard as a supported OBDAI feature; supported Mode 6 tests provide the monitor-test workflow. |
| 06 | On-board monitor-test results | Decodes supported test snapshots by ECU, monitor and test ID, with reported values, scaling and limits. ARIA can inspect and compare them. |
| 07 | Pending emissions-related DTCs | Reads pending faults that may not yet have matured into stored codes. |
| 08 | Control of on-board tests/components | No general Mode 08 control workflow is exposed. This is not a claim of bidirectional actuator tests. |
| 09 | Vehicle information | Reads the supported information types below: identity, calibration identifiers, ECU name, and in-use tracking counters. |
| 0A | Permanent emissions-related DTCs | Reads permanent codes where supported. The vehicle controls their removal after its diagnostic criteria are met. |
Mode 6: ask what the vehicle’s own tests found
Readiness answers whether a monitor has completed. Mode 6 can add what a particular on-board test measured and the limits reported by the ECU. Depending on the vehicle, this may include catalyst, oxygen-sensor, EVAP, EGR, misfire, or other monitor tests.
ARIA can inspect the latest snapshot, identify values outside the reported bounds, and compare the same ECU/monitor/test across saved sessions. That can help distinguish a one-time result from a recurring pattern and guide the next check. A result near a limit is not a predicted failure date, and an out-of-range value alone is not a confirmed failed part. Manufacturer-defined or unknown tests remain identified as such.
Mode 6 is a snapshot refreshed on demand, not a continuous live sensor stream. Its age, whether the monitor has rerun, units, and test identity all matter when comparing drives.
You can inspect the supporting measurements yourself in Monitor Tests, the fault and freeze-frame views, and the live-data views. The value of the conversation is being able to ask how those pieces fit together. For inspection preparation, see Understanding emissions readiness monitors.
Mode 09: identity and context that make readings useful
Vehicle information helps ARIA put a session in context. A reported VIN helps identify the vehicle and associate saved sessions. ECU names help identify a responding controller. CAL IDs identify its calibration, and CVNs are calibration verification values; reading them alone does not certify that software is original or approved.
In-Use Performance Tracking (IPT) supplies monitoring completion and opportunity counters where supported. Together with warm-ups, distance and time since codes were cleared, these help ARIA judge how much opportunity the vehicle has had to test itself. A clean code list immediately after a reset carries different evidential weight from repeated completed tests. Counters do not prove why somebody cleared codes.
| InfoType | Information OBDAI decodes |
|---|---|
| 0x00 | Supported information-type bitmap (discovery, not a sensor) |
| 0x02 | Vehicle Identification Number (VIN) |
| 0x04 | Calibration identifications (CAL ID) |
| 0x06 | Calibration Verification Numbers (CVN) |
| 0x08 | In-Use Performance Tracking, spark ignition |
| 0x0A | ECU name |
| 0x0B | In-Use Performance Tracking, compression ignition |
These seven common reference entries include the support bitmap; they are not the entire vehicle-information decoder or a guarantee of seven populated fields from every controller. Current decoding also includes supported engine/certification identifiers, protocol identification, fueled-engine ignition-cycle and EVAP-decision distance counters, vehicle-operation blocks, and plug-in-hybrid distance/fuel/grid data. Availability depends on the vehicle and diagnostic path, including OBDonUDS F8xx information. Missing vehicle information is not proof of a fault.
What “220 parameter definitions” actually counts
The current OBDAI Service 01 catalog contains 220 distinct PID entries, spanning 0x00–0xDC with 0xCA absent. This is the implemented catalog based on the April 2024 SAE J1979DA data set, not a promise to cover every future revision. It includes seven supported-PID bitmaps and status, counter, configuration, and measurement definitions. It does not mean 220 physical sensors, 220 simultaneous readings, or 220 readings on your car.
The category tables below contain 126 reference rows representing 144 distinct PID addresses after expanding ranges. The other 76 catalog entries comprise the seven support bitmaps and 69 additional definitions not individually listed in those tables. For example, one row for 0x24–0x2B represents eight PID addresses. Separately, one PID such as 0x14 can return both oxygen-sensor voltage and fuel trim; those are multiple signals from one definition, not two entries in the 220 count.
The additional definitions cover ambient temperature and test-equipment configuration; newer fuel, NOx, EVAP and aftertreatment data; gear and odometer information; and extended electrified-powertrain data. Examples include 0xA6 odometer, 0xB2–0xBF and 0xC1–0xC2 high-voltage energy-storage data, 0xCC/0xCD motor RPM/torque, 0xD0 battery metrics, 0xD1 transmission oil temperature, 0xD2 certified energy/range, and 0xD5 fuel-cell data. Within 0xB2–0xBF, signals include charge rate, temperature, current, voltage, state of charge, capacity, power, energy and state of health.
Those decoders only help when the vehicle exposes the corresponding standard data. They do not unlock proprietary battery packs or guarantee EV battery-health coverage. See Hybrid & EV vehicle support.
Service 01 reference: common and extended data families
This is a compact reference, not the full 220-entry inventory. OBDAI discovers the supported PIDs on connection. A multi-signal definition may contain supported and unsupported sub-signals; logging selection and sampling also affect what ARIA can analyze over time. Units below describe the signals; displayed units can change with the app’s Metric / US setting.
Core Engine
| PID | Description | Units |
|---|---|---|
| 0x04 | Calculated Engine Load | % |
| 0x05 | Engine Coolant Temperature | °C |
| 0x0B | Intake Manifold Absolute Pressure | kPa |
| 0x0C | Engine RPM | rpm |
| 0x0D | Vehicle Speed | mph |
| 0x0E | Ignition Timing Advance (Cyl #1) | ° |
| 0x0F | Intake Air Temperature | °C |
| 0x10 | Mass Air Flow Rate | g/s |
| 0x11 | Absolute Throttle Position | % |
| 0x1F | Time Since Engine Start | sec |
| 0x42 | Control Module Voltage | V |
| 0x43 | Absolute Load Value | % |
| 0x5C | Engine Oil Temperature | °C |
Fuel System
| PID | Description | Units |
|---|---|---|
| 0x03 | Fuel System Status (Bank 1 & 2) | status |
| 0x06 | Short Term Fuel Trim — Bank 1 & 3 | % |
| 0x07 | Long Term Fuel Trim — Bank 1 & 3 | % |
| 0x08 | Short Term Fuel Trim — Bank 2 & 4 | % |
| 0x09 | Long Term Fuel Trim — Bank 2 & 4 | % |
| 0x0A | Fuel Pressure (gauge) | kPa |
| 0x22 | Fuel Rail Pressure (relative to manifold) | kPa |
| 0x23 | Fuel Rail Pressure (direct injection) | kPa |
| 0x2F | Fuel Level Input | % |
| 0x44 | Fuel/Air Commanded Equivalence Ratio | λ |
| 0x51 | Fuel Type Currently Utilized | type |
| 0x52 | Alcohol Fuel Percentage | % |
| 0x59 | Fuel Rail Pressure (absolute) | kPa |
| 0x5D | Fuel Injection Timing | ° |
| 0x5E | Engine Fuel Rate | L/h |
Oxygen Sensors — Narrowband
| PID | Description | Units |
|---|---|---|
| 0x13 | Location of Oxygen Sensors | bitmap |
| 0x14 | O2 Sensor B1-S1: Voltage & Fuel Trim | V, % |
| 0x15 | O2 Sensor B1-S2: Voltage & Fuel Trim | V, % |
| 0x16 | O2 Sensor B1-S3: Voltage & Fuel Trim | V, % |
| 0x17 | O2 Sensor B1-S4: Voltage & Fuel Trim | V, % |
| 0x18 | O2 Sensor B2-S1: Voltage & Fuel Trim | V, % |
| 0x19 | O2 Sensor B2-S2: Voltage & Fuel Trim | V, % |
| 0x1A | O2 Sensor B2-S3: Voltage & Fuel Trim | V, % |
| 0x1B | O2 Sensor B2-S4: Voltage & Fuel Trim | V, % |
| 0x1D | Location of Oxygen Sensors (alternate) | bitmap |
Oxygen Sensors — Wideband (Lambda)
| PID | Description | Units |
|---|---|---|
| 0x24–0x2B | O2 Sensors B1/B2 S1-S4: Equiv Ratio & Voltage | λ, V |
| 0x34–0x3B | O2 Sensors B1/B2 S1-S4: Equiv Ratio & Current | λ, mA |
| 0x55 | Short Term Secondary O2 Trim — Bank 1 | % |
| 0x56 | Long Term Secondary O2 Trim — Bank 1 | % |
| 0x57 | Short Term Secondary O2 Trim — Bank 2 | % |
| 0x58 | Long Term Secondary O2 Trim — Bank 2 | % |
| 0x8C | O2 Sensor (Wide Range) Extended | λ, % |
Catalyst & Emissions
| PID | Description | Units |
|---|---|---|
| 0x3C | Catalyst Temperature B1-S1 | °C |
| 0x3D | Catalyst Temperature B2-S1 | °C |
| 0x3E | Catalyst Temperature B1-S2 | °C |
| 0x3F | Catalyst Temperature B2-S2 | °C |
| 0x2C | Commanded EGR | % |
| 0x2D | EGR Error | % |
| 0x69 | Commanded EGR and EGR Error | % |
| 0x6B | Exhaust Gas Recirculation Temperature | °C |
| 0x12 | Commanded Secondary Air Status | status |
| 0x2E | Commanded Evaporative Purge | % |
| 0x32 | Evaporative System Vapor Pressure | Pa |
| 0x53 | Absolute Evap System Vapor Pressure | kPa |
| 0x54 | Evap System Vapor Pressure (Hi-Res) | Pa |
Throttle & Pedal Position
| PID | Description | Units |
|---|---|---|
| 0x45 | Relative Throttle Position | % |
| 0x47 | Absolute Throttle Position B | % |
| 0x48 | Absolute Throttle Position C | % |
| 0x49 | Accelerator Pedal Position D | % |
| 0x4A | Accelerator Pedal Position E | % |
| 0x4B | Accelerator Pedal Position F | % |
| 0x4C | Commanded Throttle Actuator Control | % |
| 0x5A | Relative Accelerator Pedal Position | % |
| 0x6C | Commanded Throttle & Relative Position | % |
| 0x8D | Absolute Throttle Position G | % |
Diagnostic Status
| PID | Description | Units |
|---|---|---|
| 0x01 | Monitor Status Since DTCs Cleared | status |
| 0x02 | DTC That Caused Freeze Frame | DTC |
| 0x1C | OBD Standards Compliance | type |
| 0x1E | Auxiliary Input Status | status |
| 0x21 | Distance Traveled While MIL Active | km |
| 0x30 | Warm-ups Since DTCs Cleared | count |
| 0x31 | Distance Traveled Since DTCs Cleared | km |
| 0x41 | Monitor Status This Drive Cycle | status |
| 0x4D | Engine Run Time While MIL Active | min |
| 0x4E | Engine Run Time Since DTCs Cleared | min |
| 0x5F | Emission Requirements | type |
| 0x65 | Auxiliary Inputs/Outputs | status |
Turbocharger & Boost
| PID | Description | Units |
|---|---|---|
| 0x33 | Barometric Pressure | kPa |
| 0x6F | Turbocharger Compressor Inlet Pressure | kPa |
| 0x70 | Boost Pressure Control | status |
| 0x71 | Variable Geometry Turbo (VGT) Control | status |
| 0x72 | Wastegate Control | % |
| 0x73 | Exhaust Pressure | kPa |
| 0x74 | Turbo RPM | rpm |
| 0x75 | Turbocharger A Temperature | °C |
| 0x76 | Turbocharger B Temperature | °C |
| 0x77 | Charge Air Cooler Temperature (CACT) | °C |
Diesel-Specific
| PID | Description | Units |
|---|---|---|
| 0x6A | Commanded Diesel Intake Air Flow | % |
| 0x6D | Fuel Pressure Control System | kPa |
| 0x6E | Injection Pressure Control System | kPa |
| 0x78 | Exhaust Gas Temperature Bank 1 | °C |
| 0x79 | Exhaust Gas Temperature Bank 2 | °C |
| 0x7A | Diesel Particulate Filter (DPF) Bank 1 | kPa |
| 0x7B | Diesel Particulate Filter (DPF) Bank 2 | kPa |
| 0x7C | DPF Temperature | °C |
| 0x83 | NOx Sensor | ppm |
| 0x85 | NOx Control System | status |
| 0x86 | Particulate Matter (PM) Sensor | mg/m³ |
| 0x8B | Diesel Aftertreatment Status | status |
| 0x92 | Fuel System Control (Compression Ignition) | status |
Torque & Performance
| PID | Description | Units |
|---|---|---|
| 0x61 | Driver’s Demand Engine Torque | % |
| 0x62 | Actual Engine Torque | % |
| 0x63 | Engine Reference Torque | Nm |
| 0x64 | Engine Percent Torque Data | % |
| 0x8E | Torque Friction Percent | % |
Hybrid
| PID | Description | Units |
|---|---|---|
| 0x5B | Hybrid Battery Pack Remaining Life | % |
See Hybrid & EV Vehicle Support for more details.
Extended Engine Data
| PID | Description | Units |
|---|---|---|
| 0x66 | Mass Air Flow Sensor (Extended) | g/s |
| 0x67 | Engine Coolant Temperature (Extended) | °C |
| 0x68 | Intake Air Temperature Sensor (Extended) | °C |
| 0x7F | Engine Run Time (Extended) | sec |
| 0x81–0x82 | Engine Run Time for AECD #1-10 | sec |
| 0x84 | Manifold Surface Temperature | °C |
| 0x87 | Intake Manifold Absolute Pressure (Extended) | kPa |
| 0x89–0x8A | Engine Run Time for AECD #11-20 | sec |
| 0x98–0x99 | Exhaust Gas Temperature (Extended) | °C |
Emissions Compliance (WWH-OBD)
| PID | Description | Units |
|---|---|---|
| 0x7D | NOx NTE Control Area Status | status |
| 0x7E | PM NTE Control Area Status | status |
| 0x88 | SCR Induced System Actual State | status |
| 0x8F | Particulate Matter Sensor Output | status |
| 0x90–0x91 | WWH-OBD Vehicle/ECU System Info | status |
| 0x93 | WWH-OBD Vehicle OBD Counters | hours |
| 0x94 | NOx Control Driver Inducement Status | status |
| 0x95 | SCR Catalyst NH3 Storage Data | status |
Put the evidence to work
Ask ARIA: “Explain the codes, readiness and monitor-test results together. What is supported by this session, and what should I check next?” For newer supported OBDonUDS vehicles, explore OBDAI PRO with GEN2.
Need a parameter that is not shown here? Email support@obdai.app with the PID or DID, your year/make/model, and any available format documentation. A missing response may be a vehicle or protocol limitation, not an absent decoder.