1999 Blazer Code PO147
 

This past weekend the Service Engine Soon light came on so I drove over to Advance Auto to get a scan. It showed code PO147 which I was told is the downstream O2 sensor after the cat. They had replacement sensors in stock with a few choices. Should I buy a particular brand and stay away for others? I do use AC Delco for some parts but was told that this sensor is after the cat so it is not as important as the up stream sensors.

Any thoughts?

P0147 is indicating a problem in the heater circuit for the O2 sensor downstream of the converter. It monitors the converter and has no affect on engine performance. The problem could be in a circuit for the sensor, or the sensor itself. It needs to be diagnosed if you want to know for certain what the problem is. AC Delco or Denso sensors are your best options, and Denso is usually cheaper.

Thanks Captain. I figure if I have to go to the trouble of removing the sensor, I might as well replace it and see what happens. I have never replaced any of the sensors since the car was new. I know others have removed the sensor and swapped it with the one in front of the cat and see if it throws a different code telling you that the sensor is bad.

Keep us posted on the results.

The code should tell you which one to swap, there is no need to waste your time swapping the sensors around to find the bad one. I'd imagine it's the sensor unless your wires going to the sensor location got damaged somehow.

That's exactly correct. Without going through the flow chart to diagnose the problem, swapping the sensor is the next best way to test it, (let the PCM diagnose the problem for you). If the DTC changes, the sensor is the problem. If DTC remains the same, the sensor is not the problem.

Follow up on PO147 code.

Finally got around to replacing the 02 sensor yesterday after the cat. It was a tough breaking loose the sensor as it was original. The old sensor looked pretty burned up on the tip. Will my CEL go off by itself or will the code need to be cleared?

The light will go off after a certain number of consecutive warm ups/drive trips without a fault. If you clear the codes, the light will remain off unless a problem is detected after all of the monitors run and complete their tests.

Thanks Captain, that's what I thought. I don't have a scanner to clear the code so I will wait for it to clear itself. My daughter uses this truck for school so I will tell her to keep an eye out on the service engine light.

Code update.

Daughter told me the Service Engine Light has gone off. Thanks again for solving another issue!