Hi, i connected my odb2 scanner to my truck to check the health of the o2 sensors because of issues I'm having. The first sensors on both banks were reading 0.1v - 0.2v which i understand means the engine is running lean. the second o2 sensors (on the catalytic converter) both read from 0.7v - 0.9v. is it normal for one set of o2 sensors to read lean and the other set to read rich?? or is this evidence of a leak in the manifold? Please help

 

When looking at the upstream goal voltage, it should fluctuate above and below the normal center (.4 to .6 volts) based upon what the downstream O2 sensor is reading. The vehicle should be driven through all speed ranges when checking goal voltage. If the goal stays high or low all the time, a thorough check of the downstream oxygen sensor should be made. Be sure you check the sensor, wiring harness, connectors, catalytic converter, and inspect for exhaust leaks.
Although a MIL lamp may not be illuminated, there are instances when the downstream O2 sensor goal voltage is out of range, causing driveability problems or low fuel economy.
If the downstream O2 sensor tends to stay below center all the time, the PCM will adjust the goal voltage higher in an effort to correct the low O2 readings of the downstream sensor. This can result in low fuel mileage.
If the downstream O2 sensor has a tendency to stay above center, the PCM will set a low goal voltage which results in a lean fuel mix which can cause the engine to run hotter and aggravate a spark knock condition.
Sometimes a service technician will reset the PCM and take it for a test drive. The PCM does a recalibration after the reset, and the problem may go away until the PCM has completed a relearn of the system and then begins to attempt to correct for the downstream sensor error. If the symptoms reappear after several days of driving after a service is performed, check the downstream O2 sensor, the exhaust system, the wiring, and the catalytic converter. Note: a worn out catalytic converter can produce symptoms similar to a bad downstream O2 sensor.

 

Thank you for the information. my truck runs great when i cold start it, especially in the morning. after a couple of minutes of driving, it just bogs down. i'll take it to a personal friend mechanic to take a look at it during the week. hopefully its just a leaking manifold. i do hear weird sounds from under the car when i start it. like a whooshing sound and ticking sound as well.