2006-09-22 22:06:33 · 3 answers · asked by Anonymous in Cars & Transportation ➔ Other - Cars & Transportation
vwhobo:Your awnser makes perfect sense to me
2006-09-23 01:33:52 · update #1
I'm not sure what you mean by "main O2 sensor". Additionally if one O2 sensor on a car is heated, they all (2,3,4?) are. But...
Newer model cars and all OBD-II compliant vehicles use heated oxygen sensors (HO2S) simply because the engine management system will not enter closed loop until the HO2S reaches a temperature of about 600 degrees Fahrenheit. While the car is running in open loop, it's using a map in the PCM to guestimate the air/fuel ratio. Once it goes into closed loop, the exhuast oxygen content is monitored by the HO2S and reported to the PCM which uses it to determine the A/F ratio. The PCM regulates fuel flow for increased economy and lowered emissions. Cars with HO2S's generally are running in closed loop mode within 30 seconds even on the coldest days.
Upstream HO2S's only are the ones responsible for reporting the oxgen content and therefore A/F ratio. Downstrean sensors are only used to determine catalytic converter efficiency. Clear as mud, right?
2006-09-23 00:27:22 · answer #1 · answered by vwhobo 4 · 0⤊ 0⤋
Because they don't work very well when they're cold. The ones without heated elements are heated by the exhaust, but adding a heater lets them warm up faster.
2006-09-23 08:24:04 · answer #2 · answered by Mad Scientist Matt 5 · 0⤊ 0⤋
It helps give a more accurate reading when you first start up the car & idle it.
2006-09-23 08:12:29 · answer #3 · answered by Dave 5 · 0⤊ 0⤋