Some diagnostic info:
The oxygen sensor that trouble code P0157 refers to, is located in the rear of the exhaust and behind the catalytic converter. ... When this code is stored by the power control module (PCM), it means that the oxygen sensor has remained at a low voltage for too long.
More:
The low voltage signal means lean air fuel mixture, or too much oxygen and too little fuel. ... The code P0131 is set when the signal voltage from the front O2 sensor is stuck low. In modern cars, the air fuel ratio sensor (A/F sensor) is used instead of the O2 sensor, but it's also often referred to as a front O2 sensor.
More:
Repair any exhaust leaks before the sensor to prevent excess oxygen getting into the exhaust stream causing the low voltage readings. Check the O2 sensor for oil or coolant contaminants that could foul the sensor. Repair any harness that is damaged properly to prevent erratic readings from the sensors.
Is related to the rear O2 sensor. How old are the sensor(s)? Plus it sure would help to have your rig info. All 91 to 99 rigs are not the same.
We recommend that you put all your rig(s) info in your signature so we all don’t have to guess at year, make, model, engine size, trans, rear axle locker…….etc. While you may have posted pertinent info in your first post, you may forget to do it again and the info is needed by us anyway. Makes it way easier on all members that attempt to help, to have that info right up front. It is also recommended that you take a pic of your RPO codes, on the inside cover of the glove box, and post that image in your signature. All this info will greatly help those that will try to help with a problem.
If there is any other info, like upgrades, mods or recent mechanical/maintenance work done, that would be helpful in any post as well. Too many times a question is asked by the poster and after about 10 responses we find out that the poster has done recent work to attempt to fix the problem or work that was done that SEEMS not related to the problem.
