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By the '90s, OBD-I systems had become much more sophisticated as they were put to use controlling multi-port fuel-injection systems. But the systems still lacked uniformity among the manufacturers and accessibility to information to the aftermarket and independent repair shops. To remedy this situation, the government mandated a standardized system of trouble codes and required the manufacturers to give access to the codes and data stream to Independent shops. The resulting system was dubbed OBD-II. It still operates much the same way as OBD-I, utilizing oxygen sensor readings to adjust fuel trim and deliver the most efficient air/fuel ratios, but It Is much more sophisticated and features numerous redundant checks and monitoring systems. Simply put. the ECM has several ways to check most of the sensors to verify that they are working correctly. As a result, the trouble code system was revised to four-digit codes instead of the two- (and in some cases three-) digit codes of the previous system.

Here are oxygen sensors before and after the catalytic converters verify the cats are working properly.

The other major change with OBD-II is the addition of a second oxygen sensor after the catalytic converter. This is to ensure the cats weren't removed and they are functioning properly and reducing harmful emissions.

All OBD-II cars share the same connector.

Galpin Ford's Johnny Stein demonstrates Ford's Integrated Diagnostic System, a PC-based ECM scan tool. It is available to retail customers but is very expensive and requires annual renewal fees. You also have to upgrade it every year, and that isn't free. Stein guesses he's invested nearly $4,000 of his own money to pay for his equipment.

You don't need to buy the latest, most expensive scan tool on the market, but we do recommend buying one that will read your car's data stream. Look to spend about $200. Some parts stores may have a few available to rent if you want to try one out before buying it.

The new system requires a new set of scanners to read the date and trouble codes. You must use a scanner; there are no more jumper wires and blinking check engine lights. But the good news is one scanner can read any make or model, foreign or domestic, and all OBD-II cars have the same set of trouble codes and the same 16-pin data link connector.

You don't need to buy the latest, most expensive scan tool on the market, but we do recommend buying one that will read your car's data stream. Look to spend about $200. Some parts stores may have a few available to rent if you want to try one out before buying it.

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