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Hi guys,

My 4G15 ECU has been throwing the fault code "42" for over a year now, which references to "Fuel System Error", but the car is running fine. After its latest emissions inspection, hydrocarbon emmissions were 1 point below the legal limit (whew!). My first thought is that it's my O2 sensor. I tried to find a replacement through the local chain auto parts stores, but the best the guys could do for under $100 was get a 4-wire unit, and have me not hook up the heater wires.

I'm not afraid to jury rig an O2 sensor to save a few bucks, but I'd like to know more about 2-wire vs 4-wire units. Any information would be appreciated.

Gm cars in the past used a one wire sensor. Exhaust was the ground . A two wire sensor has a wired ground. An O2 sensor starts working good around 600 degrees . To improve emissions a four wire sensor with a heater is to get it up and running sooner. In some cases running at all because how far down the exhaust stream the o2 is mounted . A four wire should work. Heating to temp is not a problem with a manifold mounted O2.

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91 colt gl 4g37/5m22 from 94 T/E/L mustang 5.0