kingrukus

I just diagnosed the check engine lamp with my Diablosport Predator Tuner and my 2000 GT 5-speed is throwing several codes:

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
I am thinking this might be caused by the cats on my Bassani X pipe being too weak? What else do you think would cause this?

P0721 - Output Shaft Speed Sensor Range / Performance
I am thinking this is being caused by my speedo recal that the previous owner installed after installing the 3:73 gears? What else would cause this?

P0174 - System Too Lean (Bank 2)
I have no idea what would cause this. This one scares me.

P1000 - OBD System Readiness Test Not Complete
No idea what would cause this?

Any clues would be highly appreciated.

cliffyk

Click here for more about P0420. Work the possible cause list from top to bottom.

Ditto on P0721. The speedometer re-calibration unit's wiring could be causing the problem. On the '99 through '04 the OSS signal feeds the PCM, and the PCM sends data packets to the instrument cluster so that its microcontroller can drive the gauge.

Here's the shop manual info for P0174 (same causes as P0171)

Where it's just one bank I would first check for exhaust leaks before or near the sensor, or wiring problems/bad sensor (they tell the PCM the mix is lean when they fail).

P1000 means that the I/M (Inspection/Maintenance) OBDII monitoring tests are incomplete--more about that here. DTC P0174 would cause this.