I've got a stock '99 Protege 1.8L, 223,000 km that's been setting off the MIL light for about three weeks with code P1170. I need to do an emissions test soon and it's time to get it fixed. I'm looking for some help understanding the problem.

The car really doesn't show any signs of running poorly, I assume it's going into open loop running mode which is keeping everything happy. All the regular maintenance is done, spark plugs, wires, filter, pcv are new or near new.

My understanding of this code is that the bank1 sensor 1 oxygen sensor is not cycling between rich and lean. The code is set after 43 seconds of consecutive readings. I backprobed the front (Upper) O2 sensor while revving the engine in neutral and found it to vary in voltage as I would expect it to, oscillating between .2 and .8 volts. Never once did I see it sit either above or below .45 volts for more than a couple seconds.

I next took a look at the MAF, which looked very clean when I disassembled it. I'm not sure if I can clean the hot wire style in this protege, is it safe to do with electric contact cleaner? Anyhow, I backprobed this as well and found that with the key on and the engine not running I read 1.44 volts. At idle this went to 2.02 volts. I also revved it up and got only 2.76 volts to read, revving and holding at a high RPM (not sure exactly, maybe 4000RPM as I was under the hood). What is the voltage range of this sensor and are the readings in the acceptable range?

The light seems to always come on after I've been on the highway for a couple exits, usually corresponding with easing up on the gas pedal a bit.

When the check engine light is on, is the PCM in open loop, and does it take readings from the MAF to set the air fuel ratio? What sensors are used in open loop?

Any help would be appreciated. Thanks.

 

Strike another site off the SETI list, no sign of intelligent life here. It turned out to be a lazy O2 sensor if anyone is interested.

 

Thanks.