2005 Chevrolet Silverado 1500 LS 5.3L surging mil lamp on

Truck Question:

We just installed a used engine on my 2005 Chevy Silverado 3 months ago. It ran good but lately, idling is way off like going up and down. Checked with my scanner and showed faulty O2 sensor bank 1 and 2. Is this an automatic sensor replacement?

ATS Adviser:

Not necessarily, however you can quickly verify that. Using a generic scanner, go to your live data stream and scroll on the long term fuel trim (LTFT) and short term fuel trim (STFT) data. You can see it at the fuel system data monitor. Watch the values shown in %. With engine warmed up, a normal reading on both fuel trims should +10 % to -10 %. High + reading means itís running lean and reverse is rich.

The oxygen (O2) sensor should have a reading in millivolt which should fluctuate or oscillate between 100 to 900 mv. Normal reading should be about 450 mv with bank 1 sensor 1 terminal wire (upstream sensor) removed. To check the voltage values of the sensor, test all the H02S signal (purple wires) voltage when engine is in close loop. Any reading going to a steady flat line or spiking higher than 900 mv is a suspect. Downstream voltage is an indicator of catalytic converter (CAT). Slow fluctuation in these bottom sensors means a bad CAT. Shown below is a rough diagram.

Check this approximate 2005 Chevrolet Silverado power supply wiring diagram for the oxygen sensors.

You can get an exact FREE wiring diagram from most parts stores while buying the parts or get it FREE online 24/7 when you join ATS.

Final Fix:

Awesome! It was the upstream oxygen sensors. Thanks.

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