This section will address "E/E Diagnostic Test Modes: Onboard Diagnostics II on Unified Diagnostic Services (OBDonUDS), SAE 1979-2
1. Unified Diagnostic Services (UDS) is a new software program that will reformat how diagnostic information is displayed using a Generic Scan Tool (GST). It will organize diagnostic services into user-friendly groups and provide more detailed diagnostic information. These new UDS services for OBD will be called “OBDonUDS" and will use SAE J1979-2 standards.
It will require a new communications protocol, ISO 14229. Scan tool manufacturers are currently developing the software to meet the requirements. It will still use CAN communication (i.e., pins 6 + 14) through the current OBD-II connector (SAE J1962). These vehicles must use J1979-2 for all OBD-II communications and will not respond to protocols that are currently used. OBDonUDS includes classic J1979 Modes $01 to $0A and features such as DTC-specific Readiness Flag test results and IUMPR to OBD.
2. Implementation of OBDonUDS is for all LD and MD OBD II vehicles. The system will be installed on some 2024/2025/2026 model-year vehicles. The number of vehicles equipped with the services each model year is up to the manufacturers. It is expected that full implementation will occur with the 2027 model-year vehicles.
3. OBDonUDS Data Enhancements will include 1) expanded readiness group categories, 2) redefined readiness completion requirements for misfire, fuel system, and comprehensive components, 3) added DTC status byte to provide DTC-specific readiness and other DTC-specific info (i.e., pending status, confirmed status, and complete this drive cycle), 4) Enhanced freeze frame support to 5 DTCs where each DTC will have two allotted freeze frames (one for the first occurrence and the second for the most recent event), 5) expanded DTC naming to 3 bytes (no longer using 2-byte DTCs), added failure type byte (FTB) to current DTC names to create more DTCs available for use, 6) and added evaporative system (EVAP) sealing functionality.
4. SAE J1979 versus SAE J1979-2 Standards:
| OBD Functionality | SAE J1979 (OBDII) | SAE 1979-2 (OBDonUDS) |
| Powertrain Data/Readiness Status | MODE $01 | Service $22 |
| Freeze Frame Data | MODE $02 | Service $19/$04 |
| Confirmed DTC | MODE $03 | Service $19/$04 |
| Clear Emissions Data | MODE $04 | Service $14 |
| DTC Test Results | MODE $06 | Service $19/$06 |
| Pending DTCs | MODE $07 | Service $19/$42 |
| Request Control | MODE $08 | Service $31 |
| Vehicle Information (CAL ID and CVN) | MODE $09 | Service $22 |
| DTC In-Use Monitor Performance Ratio (IUMPR) | MODE $09 | Service $19/$06 |
| Permanent DTCs | MODE $0a | Service $19/$55 |
*List of DTCs within each Readiness Group | No Support | Service $19/$56 |
| *List of DTCs that support IUMPR* | No Support | Service $19/$1A/$91 |
| *List of DTCs that support DTC Test Results* | No Support | Service $19/$1A/$92 |
| *Supplemental Monitor Activity Data* | No Support | Service $19/$06 |
*New to OBDonUDS* |
To better understand MODE $09 and IUMPR, refer to the section about OBDII MODES $01 - $0a.
5. How will this impact current I/M programs?
It will require a software or hardware update to the Generic Scan Tool (GST)and more memory to account for the new, more significant message responses. The I/M database storage must be updated to account for new data (both size and format). New readiness categories will be used as additional failure criteria (more data to determine if the vehicle ran its emissions monitor test before an I/M test). The additional data can be used for fraud detection and give more insight into the performance of emissions monitor tests.