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On Board Diagnostic
This system allows the engine control unit (ECU) to monitor the performance of various emissions
control devices, and alert the vehicle owner or service technician of a potential problem with
emissions management.
OBD was first introduced to the North American market in 1992. The first version is commonly
referred to OBD1. This configuration lasted through the end of the 1995 model year. Fuel injection
became commonplace in Civics starting in 1988, though the Si versions of the CRX and Civic had
fuel injection as early as 1985, and was introduced in the Integra with the launch of the 1986
Acura line. Before 1992, there was little if nothing in the way of on board diagnostics in the ECU.
The 1988 to 1991 is commonly referred to as pre-OBD or OBD0 (the 0 meaning no OBD).
Starting in 1996, OBD made some big advancements and was now referred to as OBD2. It now
became apparent that emissions had to be cut, and maintained at reduced levels for extended
mileages or periods of time. The ECU now monitored the crankshaft speed to see if fluctuations
occurred that would point to lean mixtures or a failing ignition system. It also monitored the
efficiency of the catalytic converter via a second oxygen sensor mounted downstream of the cat.
This meant that those of us that wanted to run a test pipe to eliminate the restriction associated
with the catalytic converter were faced with check engine lights as the ECU would detect lost
efficiencies due to the lack of the cat, or O2 sensor failures from the removal of the sensor.
Several products hit the market that were intended to simulate an O2 sensor and fool the ECU
into thinking that the cat was still operating efficiently. Its a little known fact that the check engine
light for the 2nd O2 sensor, or for the missing cat will not lead to the ECU operating in "limp
home" mode. It just simply leaves a glowing light on the dash to annoy you. OBD2 also added a
pressure monitor in the gas tank to insure that the pressures were building normally inside the
tank to indicate a properly closed gas cap and normally functioning evaporative emissions control
system. In 1999/2000, the connections on OBD2 ECUs were moved around, making them
completely incompatible with the 1996-1998/1999 chassis and ECUs.
Though the ECUs from the JDM 1996 and up cars appear identical to their North American
counterparts, they are very much the same as the USDM OBD1 ECUs in their operation, lacking
the crank speed fluctuation and fuel tank pressure sensors, as well as the 2nd O2 sensor from
the USDM OBD2 cars. This makes them ideal for those wanting to run the JDM ECU that was
supplied with their 1996 and up JDM engine swap in their 1988-95 car. For those of you ambitious
enough to try and use the North American OBD2 ECU from your 1996 and up USDM swap, look
forward to lots of extra work incorporating the fuel tank pressure sensor, as well as the extra O2
sensor or one of the many O2 sensor simulators on the market.
One thing to keep in mind anytime you are swapping an engine from a different generation of
engine management into your car is to stay with your existing engine wiring harness. It is always
100 times easier to make the necessary mods to the engine harness that came with your chassis,
then it is to make mods to the chassis harness to match the engine harness.
Integra 1988-1991
Prelude 1988-1991
Integra 1992-1995
Prelude 1992-1995
Engines JDM and USDM B16A, B18C, H22A, D16Z6, etc...
Integra 1996-1999
Prelude 1996-2001
Engines JDM and USDM B16A, B18C, B18CR, B18C5, H22A, B20B, B20Z, D16Y8, D16Y7, etc...
Integra 2000-2001
Engines JDM and USDM B16A, B18C, B18CR, B18C5, H22A, B20B, B20Z, D16Y8, D16Y7, etc...
