RTV (silicone) posioned O2 sensor

So finished up the final details on the 04 Tahoe engine replacement last Weekend. One of the details that day was connecting the exhaust tubing to the manifold in which I used "Sensor Safe" RTV at the joints, fired it up a couple hours later.

It has a CEL for o2 sensor Bank2 sensor 1 which Ohms at 24.6, others are 14,12 and 12 Ohms. I am assuming the fresh RTV took out the one upstream sensor while the other bank 1 upstream is at 14 ohms, right at the upper limit.

Question is will the sensor safe silicone cure out of will there be another o2 sensor failure in the future. I had also used the RTV on the manifold to head gasket as it was recommended on the RTV label (several weeks ago). I guess it is also possible the sensor was damaged during removal and or installation. Not looking forward to R&R and cleaning on the exhaust manifold with everything assembled.

whats the actual code for the o2?

Current Fault P0155 O@ Sensor Heater Circuit (Bank2 sensor1)

The Log also has the P0135 for Bank 1 sensor 1

that heater code is related to the o2 not warming up on its own. so being you just did a engine swap maybe you got a blown fuse, bad ground. o2 wire harness got pinched. something out of place.

or that o2 sensor just decided to check out.

"I guess it is also possible the sensor was damaged during removal and or installation"

More than likely when the sensor was removed the body was obviously torqued because of completing hot/cold thermal cycles in the exhaust bung. The torquing the body and ultimately the internals of the sensor including the heater winding likely caused the heater windings to overlap and short together which lowers the heater's overall resistance. Ohms law states resistance goes down while voltage stays the same so the current must go UP. She is likely drawing too much current now for warmup. Your measured 24.6 ohms, was that on the heater circuit of the sensor or the 02 sensor part? The only purpose of the heater is to preheat the sensor tip because it takes so long for the exhaust to do it and get it up to temp. This allows the engine to go into closed loop faster. An 02 sensor has to get pretty hot at the tip to give accurate readings of 02.

RTV gasses off fully in 6-12hrs usually. 24hrs for sure. After that then it is no longer a danger to the 02 sensor.

The fuse IS blown on the OB2A circuit. The connector for the sensor is above the transmission so I will need to look over the wiring for a pinch in that area along with the sensor separately.

If the silicone has cured out, I guess the exercise of cleaning it from the exhaust connections is not necessary, that is a relief.

Thank's very much for all the information!

firsthere said:

The fuse IS blown on the OB2A circuit. The connector for the sensor is above the transmission so I will need to look over the wiring for a pinch in that area along with the sensor separately.

If the silicone has cured out, I guess the exercise of cleaning it from the exhaust connections is not necessary, that is a relief.

Thank's very much for all the information!

Click to expand...

Need a multineter. Measure from heater wires (their pins at the plug) to chassis ground on the frame. They all should not be at or near zero ohms.

rockola1971 said:

Need a multineter. Measure from heater wires (their pins at the plug) to chassis ground on the frame. They all should not be at or near zero ohms.

Click to expand...

^^THIS^^ And unplug the sensor, replace the fuse, and see if it blows when you have the ignition on. Better yet, load -- with a taillight bulb or something that draws a few amps -- the two harness wires that power the heaters to see if they can carry the current. You may not need to look for wire damage if these two tests pass.

Replaced both upstream sensors with unbranded ebay units. I figured if they were to contaminate again I'd rather be out just a few bucks. I already have AC delco sensors ready to go in if, when, needed.

Anyways, the sensor must have been the problem with the short as the new ones do not blow the fuse. It Is getting a latent P0171 (bank 1 lean) with No CEL. The idle is smooth and truck runs well though. Fuel trim on bank 1 is in the lower double digits so I will re-torque the intake and check all lines and sensors fittings. Could also be the new ebay O2 units I guess.

Just for reference, by Comparison of the new ebay sensors which were at 6.2 each and both original downstream sensors (still in use) are around 12 Ohms, Should that be a concern at the higher end service range (16 Ohms max) thus need to be replaced as well? Also, does the static O2 sensor resistance change fuel trim enough to worry about as long as its within the service range...

Are you measuring the sensor resistance, or the sensor's heater resistance?