This was my first time using Eagle, and I created this circuit/board. The circuit is used in a vehicle's emissions system. When power is NOT applied to the relay, the O2 sensor signal comes in and then out to the DME. However when power IS applied, a 200 mV signal (through the potentiometer) is generated and sent to the DME (instead of the O2 signal). Trying to keep it small, currently fits on a 2x2" board and will be fitted to a plastic project box.
Opinions are welcome...
Maybe a little more background into the circuit... There is a "Secondary Air Pump" (SAP) on the vehicle, which the "Digital Motor Electronics" (DME) signals ON during a cold start. The SAP pumps air into the catalytic convertors to speed up their heating. Thus reducing emissions by making the CATs effective quicker.
When the DME signals the SAP ON it expects to see a "lean" condition from the O2 sensors due to the extra air. If it doesn't see a "lean" condition, then it assumes the SAP is faulty and you'll get a "Check Engine Light" (CEL).
The point of the 200mV signal is to temporality fool the DME into thinking there is a "lean" condition. Now it doesn’t need to be exactly 200mV, just in the ballpark.
Edited by bmwpowere36m3 - 10/8/10 at 4:29pm