OBD II standardized the connector, the codes and the scan tool. CARB says it is required on 1996 and newer gasoline cars and trucks.
OBD I and OBD II are two generations of one idea. This guide sets California’s first two OBD rules side by side, adds what CARB and EPA say about 1994 to 1996, and lists four things to check on a car.
The plain answer
OBD I was California’s first OBD regulation. It required manufacturers to monitor some emission control components, starting with the 1988 model year. OBD II is the second generation. It standardized the connector, the fault codes and the scan tool.
CARB says all 1996 and newer gasoline and alternate fuel passenger cars and trucks must have OBD II, and so must all 1997 and newer diesel passenger cars and trucks. A small number of 1994 and 1995 gasoline vehicles were equipped with OBD II, according to CARB. EPA says full compliance was not required on all light-duty cars and trucks sold in this country until the 1996 model year. CARB says owners can look for the words “OBD II” on the emission control information label attached to the underside of the hood.
The model year gets you close. CARB says the label under the hood can verify it.
What the first two California rules required
Section 1968 of Title 13 of the California Code of Regulations covers 1988 and later model years, the start CARB gives for OBD I. Section 1968.1 covers 1994 and later model years, and CARB’s 1996 statement of reasons calls its requirements OBD II. A waiver provision in §1968.1 compares designs for vehicles in production before April 1, 1994 with “systems developed according to section 1968”. The table sets the two texts side by side.
| Topic | 13 CCR §1968, the 1988 rule | 13 CCR §1968.1, the OBD II rule |
|---|---|---|
| Vehicles covered | “All 1988 and subsequent model year passenger cars, light-duty trucks, and medium-duty vehicles equipped with a three-way catalyst system and feedback control” (a). | “All 1994 and subsequent model-year passenger cars, light-duty trucks, and medium-duty vehicles” (a)(1.0). |
| Systems it watches | Malfunctions of “computer-sensed emission-related components”, of the on-board computer processor, and of “the emission-related functioning of the fuel metering device and EGR system on vehicles so equipped” (a). | Malfunctions of “any powertrain components which can affect emissions and which provide input to, or receive output from, the on-board computer(s)”, and of the computer itself (a)(1.0). |
| Warning lamp | The lamp displays “Check Engine” or “Service Engine Soon”, or another phrase the executive officer finds likely to cause a vehicle owner to seek corrective action (b). | The lamp displays “Check Engine” or “Service Engine Soon”. “Powertrain” may replace “Engine”, and an ISO engine symbol may replace the word or the whole phrase (a)(1.1). |
| Reading the information | “on-board diagnosis of the likely area of the malfunction without the aid of any external device” (a). | Fault codes “stored in computer memory”, reached through “a standardized electrical connector”, and “capable of being downloaded to a generic scan tool meeting these SAE specifications” (a)(1.2) and (k)(2.0). |
| Connector, protocol and codes | The text mentions no connector, no protocol and no scan tool. | “A standard data link connector in a standard location in each vehicle based on SAE specifications shall be incorporated” (k)(4.0). One of three named protocols carries the data (k)(1.0), and medium-duty vehicles may use J1939 with approval (k)(5.0). “Uniform fault codes based on SAE specifications shall be employed” (k)(3.0). |
Both rules include extension provisions. Section 1968(d) limits an extension to the time needed or three years, whichever comes first, and §1968.1(m) provides extensions and waivers for the early OBD II model years. CARB’s 1996 statement of reasons says California adopted OBD II in 1989. The history notes of §1968.1 on Cornell Law School’s site list a first filing in August 1990 and a last amendment in October 1999. For 2004 and later model years, California’s OBD II rule is §1968.2, the one our other guides quote.
Why California wrote OBD II
CARB’s fact sheet says OBD I systems “were limited to monitoring only a few of the emission-related components, and the monitors were not calibrated to a specific level of emission performance.” OBD II “was developed to address these shortcomings and make the system more powerful and user-friendly for service technicians.”
The 1996 statement of reasons names another goal, which is better access to service information for the aftermarket repair industry. The OBD II rule contains several requirements for standardizing diagnostic connectors, communication protocols, fault codes, engine parameter data and test equipment. In CARB’s words, those requirements “will allow independent repair shops to utilize a single diagnostic tool to access all of the information generated by the OBD II system for any manufacturer’s vehicle.”
Start dates from CARB and EPA
| Model years | What the sources say | Source |
|---|---|---|
| Before 1988 | California’s 1988 rule covers 1988 and later model years. EPA says some variety of OBD system “has been an option on certain vehicle models since the early 1980’s”. | 13 CCR §1968; EPA420-R-01-015 |
| 1988 to 1993 | California’s 1988 rule applies to vehicles with a three-way catalyst system and feedback control. EPA says OBD-equipped vehicles older than model year 1994 use “an earlier, non-standardized generation of OBD system (also known as OBD I)”. | 13 CCR §1968; EPA420-R-01-015 |
| 1994 and 1995 | CARB says “a small number of 1994 and 1995 model year gasoline vehicles were equipped with OBD II systems.” EPA says the federal OBD requirement began with the 1994 model year and that manufacturers could request waivers for 1994 and 1995. | CARB fact sheet; EPA420-R-01-015 |
| 1996 and newer, gasoline and alternate fuel | CARB says passenger cars and trucks “are required to have OBD II systems.” EPA says full compliance was not required on all light-duty cars and trucks sold in this country until the 1996 model year. | CARB fact sheet; EPA420-R-01-015 |
| 1997 and newer, diesel | CARB says passenger cars and trucks “are also required to meet the OBD II requirements.” | CARB fact sheet |
CARB says EPA requires all 1996 and newer passenger cars and trucks sold in any state to meet EPA’s OBD requirements, which “differ slightly from California’s OBD II requirements”, and that EPA accepts systems designed to meet California’s requirements. Our compatibility guide lists the start dates we could verify for Canada, the European Union, India and Brazil.
Why older systems differ
The 1988 rule requires diagnosis “without the aid of any external device”. Its text mentions no connector, no protocol and no scan tool, so nothing in it set one standard. EPA’s 2001 report says that without federal standards for OBD I systems, “the systems themselves tend to be proprietary and may not be compatible with the standardized OBD II scanners that will be used in most I/M programs”.
ELM Electronics offers an example. Before OBDII, several vehicles, “most notably those made by General Motors”, used “a very similar connector (mostly)” for their factory communications. Those vehicles typically used the ALDL protocol, which the ELM327 chip does not support.
We found no open source that describes the connector shapes of each maker’s pre-1994 system, so this guide does not describe them.
Four things to check on a car
- Find the model year and fuel. Use the start-date table. A 1994 or 1995 car needs the next step, because CARB says a small number of those gasoline vehicles have OBD II.
- Read the label under the hood. CARB says owners can look for the words “OBD II” on the emission control information label attached to the underside of the vehicle hood to verify that the vehicle has OBD II.
- Find the connector. Our connector-location guide explains where it sits, and our pinout guide covers its 16 pins. A connector that looks right may not mean OBD II. ELM Electronics notes that before OBDII several vehicles used “a very similar connector (mostly)” and typically used the ALDL protocol, which its ELM327 chip does not support.
- Try a compatible adapter. Park the car, plug in the adapter, turn the ignition on and connect. EPA’s 2001 report says OBD I systems “may not be compatible with the standardized OBD II scanners”. Our protocols guide lists checks for a car that will not connect.
The warning lamp wording does not separate the two systems. Both rules name the words “Check Engine” or “Service Engine Soon”. Our check-engine-light guide covers what a supported scan can record once the lamp is on.
Axlyne’s boundary
Axlyne reads supported standard generic OBD2 responses through a separate compatible ELM327 adapter. It does not claim to read OBD I systems, and the ELM327 data sheet says the chip does not support ALDL, the protocol that several pre-OBDII vehicles typically used. Support varies by vehicle, adapter and phone. Axlyne does not certify that a vehicle meets any inspection or emissions rule.
Official sources
- California Air Resources Board, On-Board Diagnostic II systems fact sheet, September 19, 2019
- California Code of Regulations, Title 13, §1968, 1988 and subsequent model years
- California Code of Regulations, Title 13, §1968.1, 1994 and subsequent model years
- California Code of Regulations, Title 13, §1968.2, 2004 and subsequent model years
- California Air Resources Board, final statement of reasons for the 1996 OBD II amendments
- U.S. EPA, Performing Onboard Diagnostic System Checks as Part of a Vehicle Inspection and Maintenance Program, EPA420-R-01-015, June 2001
- ELM Electronics, ELM327 data sheet