stevesxm

codes say one or two O2 sensors need changing on this 2003 grand cherokee overland with the big V-8 ....

question one : i understand there are four total.. front and rear each bank... are they all the same , i.e. smae part number for all four ?

question two: this car only has 25,000 miles on it or so and the fuel milage is horrible . where this car lives it does short trips ( but there is hi ambient air temp so it warms right up ) and seldom if ever sees 50 mph . its all stop and go. all that considered it only gets about 9 mpg doing this driven VERY conservatively. i've had cars with bad O2 sensors before and they never had that dramatic effect on fuel economy... do these cars milage turn to garbage if an O2 sensor is bad ? i would have thought this car would do 15 mpg around town...

there are no other codes and the car runs perfectly except for the CEL light which is the O2 Codes. if i clear them they come right back. im going to change them as soon as i get some but im curious if they could be killing the milage...

dave1123

Without 02 sensor input, the PCM is relying on pre-programmed mixture settings and not changing from this. These settings would be for a cold engine so would naturally be rich. Thus the result is your poor mileage. JMHO.

stevesxm

well... we'll find out. interestingly enough, a lot of the aftermarket 02 sensors show one number only, bosch says three different numbers for the four sensors . since the bosch are direct install i suspect the difference is cable length but who knows. bosch requires the vin # and a lot of the aftermarket appear generic.

dave1123

Bosch also have the plugs on them. Most generic ones you have to splice in. The signals sent by the 02 sensors are measured in millivolts so connections need to be clean and secure, best soldered.