They perhaps have been automotive engineers' biggest challenge over the last several years. They could be the most important technologies on 1996 model year vehicles. But they won't be featured in any Super Bowl television commercials and nary a customer is likely to walk into a dealership and ask about on-board diagnostics or multiplexed wiring.

Despite their lack of glamour, on-board diagnostics (OBD) and multiplexing are critical to an industry burdened by government regulations and consumer demands for increased vehicle content and value.

The need for smarter - but hugely more complex - diagnostics is driven by federal emissions regulations. The so-called OBD-II systems (see WAW - Aug. '94, p. 48) are mandated by provisions of the Clean Air Act and by rules sent down from the California Air Resources Board (CARB). OBD-II systems are designed to monitor the performance of critical powertrain and emissions components and keep them working within a razor's edge of perfection, providing consistently low emission levels.

"Regulations are driving technology," says Francois Castaing, Chrysler Corp. vice president of vehicle engineering and general manager of powertrain operations. "(Implementing OBD-II has been) our most difficult technical challenge over the last six months."

CARB requires OBD-II to detect misfires and fuel-system evaporative losses in addition to monitoring catalytic converter efficiency, fuel metering, oxygen-sensor performance, exhaust gas recirculation and secondary air injection. Several engine components also come under OBD-II's unwavering scrutiny: camshaft position, manifold absolute pressure, throttle position coolant temperature fuel level and temperature, transmission pressures. In all, it identifies 82 fault codes.

If there are two consecutive bad readings from any one of these parts, a yellow instrument panel "check engine" light appears to prompt drivers to take their vehicle to a dealership for service.

Before the system ever made it to the assembly line, however, the big hurdle was coping with OBD-II's computing power requirements. Douglas D. Teague, Chrysler's executive engineer-powertrain planning and regulatory programs, says the current 16-bit engine control module Chrysler uses is strained to the limit by the 3 megabytes of software. The 18 inch-thick printout of the '96 LH engine control program illustrates the problem, especially when compared with the inch-thick printout of a 1982 program, which required only one kilobyte of computer capacity.

In dealing with this capacity crunch, some vehicle capabilities had to be sacrificed or changed dramatically for OBD-II. An adjustment had to be made to the cruise control system, for example.

Similarly, Ford Motor Co. engineers claim that the massive computational appetite of OBD-II has swallowed up so much capacity in its powerful EEC-V engine control module that certain models must forego some features. The 1996 Mustang GT and Cobra, equipped for the first time with Ford's 4.6L modular V-8, couldn't add traction control because OBD-II scarfed up so much of the EEC-V's capacity.

Other compromises were made within the OBD-II system itself. Some functions need constant monitoring, not unlike an antilock brake or air-bag system. Others can be tested occasionally. "It's very difficult to plan the controller," says Mr. Teague.

With the Chrysler ECU pushing the capacity envelope, Mr. Teague says the corporation already is working on a replacement. The new box, which will be on all new models by 2003, adds transmission control to the mix.

General Motors Corp. was among the first to acid-test OBD-II in actual customer vehicles, and its Service Technology Group was able to make OBD-II "fit" within the capacity of corporate electronic control modules (ECMs) - but not before an army of experts went to work.

Chrysler's Mr. Teague says drivers will not notice any difference between an OBD-II vehicle and earlier models. "Were engineers restrained from adding sophistication? Yes. That's one of our main goals, making this absolutely transparent."

More "transparent technology" coming to the forefront in 1995-'96 is multiplexed wiring systems. First introduced by GM in 1979 for engine-management systems, multiplexing now is being used in the Lincoln Continental Memory Profile System, which gives two drivers their choice of settings for features such as steering assist, suspension firmness and audio presets.

The Lincoln system is capable of communicating more than 200 functional messages. Reliability is increased because of fewer connections, says Ford. Multiplexing also saves 100 wires and 8 lbs. (3.6 kg) on the Continental.

Continental's multiplex system links 10 modules with a 2-wire bus. Modules control lighting, vehicle dynamics, driver door and seat, powertrain, air conditioning, instrument panel, ABS and traction control, the cellular phone and the stereo system.

The jury currently is out on multiplexing. Some service industry sources are offering dire reliability forecasts for early multiplexing efforts, and whispers have reached WAW that Ford already is encountering problems with the Continental, and expects them with a Taurus system as well.

Maybe it's a good thing this stuff is invisible after all.