SAE J2534 gains world acceptance for automotive reprogramming and diagnostics

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The J2534 device cable plugs into PC and under-dash OBD II connector.

SAE International's J2534 has become the “top dog” in motor vehicle reprogramming and is likely to achieve the same status in diagnostics. The standard, which enables communication between a computer and the onboard electronic databuses, also got a boost on election day: Massachusetts voters endorsed the nation’s first “right to repair” law, which specifically named J2534 as a protocol to enable independent garages to reprogram and diagnose problems in motor vehicle computers.

The impetus for J2534 came from the U.S. EPA and CARB (California Air Resources Board), which sought an affordable way for independent garages to reprogram onboard computers. The overall goal was improved vehicle emissions compliance. Prior to J2534, each automaker had its own programming system and device. It's too costly for independent garages to own all—or even most—devices.

Work began in an SAE committee in 1999 to approve specific protocols for industrywide use and incorporate them into J2534, so “Pass-Thru” devices (SAE copyrighted term) could be produced that would transfer new emissions control software from a PC to the vehicle through the under-dash OBD II connector. Eventually, five protocols were accepted, including ones from General Motors, Ford, and Chrysler. And there were early J2534-compliant systems in some Ford and General Motors cars in 2002, according to Mike Drew, whose Drew Technologies was an early developer of J2534 Pass-Thru devices.

J2534 soon also was adopted in the European Union for vehicles that had to meet EURO 5 emissions limits. Today, J2534 is used not only for reprogramming modules throughout the vehicle but also for an increasing amount of OE advanced diagnostics.

 However, there are gaps in aftermarket-available coverage, so independent garages often cannot complete a repair. Most automakers provide aftermarket reprogramming software only for emissions-related modules, to meet EPA and CARB mandates.

The Massachusetts legislature passed R2R last summer, and over 85% of the voters approved a tightening of the law on election day. R2R requires access to all OE reprogramming, dealer diagnostic, and repair information for independent garages and motorists. It’s a giant step from just emissions controls, and is likely to lead to nationwide access.

R2R was promoted by a coalition of some 40 aftermarket organizations, companies, and parts-distribution chains, including AAA (American Automobile Association). The legislative act covers cars and light trucks, effective by 2018. The voter initiative added motorcycles, RVs, and larger trucks (including construction vehicles), and it advanced the starting date to 2015—an ambitious target for many manufacturers. A negotiated compromise is expected.

Regulation began in 2004

EPA and CARB required automakers to enable J2534-based Pass-Thru aftermarket emissions reprogramming by MY2004. Many were able to use J2534 with the CAN high-speed two-twisted-wire databuses that also were being installed, per EPA mandates (with a 2008 deadline) to improve emission controls performance. For earlier OBD II models (1996-2003) and other non-CAN systems, EPA allowed use of auxiliary devices—basically special cables to tie in to the J2534-based reprogramming, as an aftermarket alternative to factory special tools.

With J2534, an OE application is loaded into a Windows PC, which enables the revised OE vehicle software to “Pass-Thru” from the PC. It continues through the J2534 device, and finally through the under-dash OBD II connector to the appropriate vehicle modules, which for emissions typically are the engine and transmission computers.

A device maker, however, may choose a limited approach. Drew Technologies, a pioneer in J2534 modules, markets single-make, lower-cost “smart” cables alongside its full-coverage units. Reprogramming also requires stable, “clean” (ripple-free) voltage within a tight range, using a suitable battery charger.

J2534-2 “infinitely expandable”

With J2534, the Pass-Thru route for vehicle software also protects an automaker’s intellectual property.

J2534 is more than 10 years old, and now has three sections. J2534-1 is the original, consisting of the emissions-related reprogramming protocols, is referenced in EPA regulations, and hasn’t changed in six years. Device makers include Drew Technologies, Actia, Bosch Diagnostics, EASE Diagnostics, Snap-On Diagnostics, Blue Streak Electronics, and Dearborn Group. All cars and light trucks sold in the U.S. are J2534-compatible for reprogramming, and emissions-software compliance (access to the software) is covered in federal regulations imposed on automakers.

J2534-2 is a “living document,” subject to new OE features, hardware, and software, prepared with instructions on introducing them in a way that fits the requirements of the standard. “It’s infinitely expandable,” said Mike Drew, president of Drew Technologies. So updating devices is not a reverse-engineering project. With the new Massachusetts law, most device makers are likely to update coverage in J2534-2.

“-2” is the section that covers single-wire CAN and other databuses for such areas as safety/anti-theft/comfort/convenience. J2534-3 is a compliance test for a J2534-1 device, to ensure it is likely to work with an OE application.

However, an automaker may decide to use other than the “standard” channels (therefore different number terminals on the OBD II connector) for CAN communications or the ISO 14230 protocol (also called Keyword Protocol 2000)—or multiple channels rather than just the standard ones. Drew’s approach to cover these possibilities, or perhaps future wireless, is to enable one of the company’s Pass-Thru tools to accept plug-in update modules.

When it comes to diagnostics, the primary alternative to an OE scan tool has been the "generic" OBD II tools, which display emissions-related trouble codes and data items, such as sensor readings. Many “professional” tools add some OE “enhanced” trouble codes and data items, but because they provide multiple-makes diagnostics, coverage is spotty.

Diagnostics through J2534

However, automakers also have been developing their latest diagnostics to run through a PC and J2534 device. Toyota and Volvo diagnostics already do; BMW/MINI is close (except for security systems) and GM's latest (Global Diagnostic System) is compliant. Other makers, particularly Ford and Honda, reportedly are close.

An exception is “Tech2Win,” the PC-based diagnostic version of GM’s long-used (1992-on) scan tool. The software was done in Europe, using ISO 22900, described by Drew as a “collection of features” that includes aspects of J2534. There is no other domestic use of ISO 22900, but J2534 devices were modified to cover Tech2Win. And although ISO 22900 also was listed in R2R, Tech2Win seems as far as it will go.

J2534 gradually is likely to become the primary approach for OE diagnostics. And if the current Toyota and GM two-day subscription rates ($55) for diagnostic or reprogramming access are typical, independent garages will find "the price is right."

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