OBD-II stands for On Board Diagnostics - second generation. BMW started putting it into the ti when it introduced the M44 engine in '96. The earlier M42 engine had an OBD first generation system.

OBD-II is a standard with separate mandates by the Federal Government and the State of California. Most car manufacturers have chosen to develop a single system that covers both mandates, instead of doing a separate version for California. In fact, part of the Federal mandate states that compliance with the California version is acceptable for compliance with the Federal version.

One of the key words in the name of this system is *diagnostics*. While there are some new requirements for reducing emissions during the warm-up sequence, and evaporative emissions, this doesn't represent a big push to further reduce the emissions from a warmed-up, properly functioning engine. A big emissions problem that has been identified is from cars that are malfunctioning and difficult to diagnose. OBD-II is primarily an attempt to make problems easier to identify and fix.

One feature of OBD-II compared to the earlier version is that there is now a standard interface for all manufacturers (actually, there are two types of plugs). This means that a shop can buy a single piece of equipment and use it to interrogate BMW's, Chevy's, Kia's, etc. There is a standardized list of parameters that can be looked at, but manufacturers are also allowed to add additional things (either published and/or secret) beyond the required list. Also, this standardized interface doesn't preclude manufacturer's from having a separate control/diagnostic interface. For us this means that a generic OBD-II test system won't be able to replace all (or even most) of the functions provided by BMW's MODIC or the DIS system.

The earlier OBD system could only detect certain major problems with the engine system. For example, if a coolant temperature sensor went completely bad, the 'Check Engine' light would come on. If the temperature sensor was only reading partially off, the earlier system couldn't tell. Another big issue was with intermittent problems. If the problem went away, it was hard to troubleshoot.

OBD-II attempts to deal with these problems. It checks engine performance. It compares sensor readings to expected values. When an error is detected, it is recorded in memory with a time stamp, and a record of what the other operating conditions were at that time. In this way, intermittent problems should be easier to identify.

The dashboard light is now called an MIL, for Malfunction Indicator Lamp. The old 'Check Engine' light was deemed an inappropriate name (for example, when the engine was actually fine, but the diagnostic system was having trouble). For most faults, the light will go out if the car goes through three run-start cycles without the problem reoccurring (the problem is still recorded in memory).

Some specific new detection features:

There is a pressure sensor in the fuel vapor recovery system to check for leaks (to cut down on evaporative emissions). A missing or loose gas cap will also be detected by this.

There are two oxygen sensors. One before the catalytic converter, one after. This allows the system to detect if the catalytic converter is functioning properly. Also, the engine management system sprays extra fuel through the engine at startup. The unburned fuel passing into the exhaust is then burned in the catalytic converter. This helps the converter to heat up faster (almost instantly) so that start up emissions can be reduced.

The system checks for misfire. By timing the pulses from a crankshaft sensor (also used for fuel injection and ignition timing), the system actually measures the crankshaft acceleration after *every* spark. If one of the cylinders isn't producing as much power as the others (bad spark, bad injector, worn valves or piston rings, etc.), it will be identified.

OBD-II engine management systems feature adaptive self-tuning. This allows things to remain optimized even as things start to wear out. (This can also cause the system to counter-act certain modifications).

Another feature that was introduced is that the engine management firmware now resides in FLASH memory. This is a newer memory technology that can be reprogrammed in circuit. It doesn't lose information when power is removed. Most earlier digital engine management systems relied on PROM or EPROM memory devices. With these it was necessary to physically remove and replace the part (the chip) from the circuit in order to change the firmware. FLASH memory can be reprogrammed simply by plugging in the right interface device to the diagnostic connector and downloading the code. (Getting the right interface device, like a MODIC, is another issue).

I view most of OBD-II as a positive development. Unlike some bungled emission control requirements of the past, it doesn't hurt performance, fuel economy, or reliability. It should make troubleshooting problems easier (even for the do-it-yourselfer, there are some fairly low-cost PC based diagnostic programs with an interface cable appearing on the market). It even appears that it should successfully help reduce emissions.

The downsides of OBD-II?

The California requirement included an anti-tamper provision. Many auto manufacturers have used this as an additional opportunity and excuse to restrict documentation and support to the aftermarket. This has lead to a strange circular block to a legal challenge. The federal courts don't find any anti-trust problems with the *law* because the federal mandate itself includes no requirement for an anti-tamper provision. The federal mandate's acceptance of the California version has been upheld because the auto manufacturers have been persuasive that having to meet two separate requirements would be an undo burden. The California version can't be charged on anti-trust issues, because technically, it only applies to a fraction of the country.

Any significant engine modification requires a remapping of the ignition and fuel curves. Because BMW doesn't offer any remapping services, and isn't giving much support to the aftermarket, it will take time for the aftermarket to reverse-engineer the system so that it can be usefully reprogrammed. This has already happened for other makes (Chevrolet for example) where there was a bigger, earlier demand. Among others, Jim C. mentioned on the bmw-digest that he will probably have code available for the M44 before the six cylinder engines. Hopefully it's just a matter of time.

Generally, I'm very much in favor of maintaining the emissions performance of an engine that's been modified. It does mean that there's a lot more work involved with making changes than in the past. This means either buying a pre-engineered total package, or going through the work of figuring out all the details and testing and adjusting things in the process. The approach of somewhat random bolt-on mods just doesn't cut it. But consider this: to have a really enjoyable, well-tuned, reliable motor, most of this type of detail work would be required anyway.

Brian Brown. BMWCCA #130878 '96 318tiS