Zfbod94

quick question.

I know on an OBD1 system you can remove the pump and as long as there is a good fuse, there will be no SES light.

So on an OBD2 system can you do the same thing? Its an 96 Impala SS. Or do you have to tune it out of the computer? Im thinking you have to tune it out because Im assuming that the O2's will be looking for that extra oxygen when the pump is running, and if its not there it will set the SES light.

Can anyone confirm or deny this?

bobdec

ODB2 checks the O2's... During the AIR test, the PCM activates the AIR pump during closed loop operation. When the AIR is activated, the PCM monitors the HO2S voltages, and monitors the short-term fuel trim values for both banks of the engine. If the AIR system is operating correctly, the HO2S voltages should be low, and the short-term fuel trim should be high.
Lights up MIL indicator (emission failure), stores DTC P0410, can be tuned out..

Zfbod94

Thanks Bob. Thats what I was looking for.

bobdec

You're correct. Looks like sometimes in later years they moved the test to closed loop. But in previous years, including OP's '96 it was tested in 'Open Loop'.

Injuneer

The GM online diagnostic guides for the 97 F-Body indicate that the P0410 diagnostic in that year was run in both open loop and closed loop. In open loop (passive test), the PCM is looking for a lean (<400mV) reading from the O2 sensors; then in open loop (active test) air pump is turned on and the PCM looks for O2 sensor readings <222mV or a fuel integrator change of at least 14 counts.

Look up the 96 B-Body to see what the system uses:

http://service.gm.com/gmspo/mode6/