I am sooo confused. This code will throw;
-when it rains out
-when i drive through puddles
-when I drive through the car wash

It will reset after awhile on its own. I know it is for high voltage and is usually a blown O2 sensor, but why when it rains or is wet?? Do I have a bigger problem that is throwing that code? TIA

 

Sounds like you have exposed wires getting wet and shorting together or to ground (the body). If you can find a wiring diagram you could trace the wires out and look for bare spots or broken insulation.

 

It does sound like a wiring issue, but I would bet that it is a faulty sensor.

P0138 is the code for high sensor volage on the B1S2 sensor which is the sensor behind the catalytic converter.

First thing I would do is unplug the connector to the B1S2 sensor and inspect the connection.

Do NOT put any dielectric grease on the connector. Newer style O2 sensors "breathe" through their wire connectors. It’s hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.

As an aside, the B1S2 sensor ONLY monitors the catalytic converter and does not have any impact on the fuel delivery to the engine. It is an emissions check only! The only problem you would run into is you may fail an inspection if your state/region uses the emissions readiness screen from the PCM.

The more I type, the more I think it is a faulty sensor...

The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading. An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor’s output voltage will drop down to about 0.1 volts. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around 0.45 volts.

The only way I would think this would cause a problem is that the water is getting into the sensor and causing it to read a higher outside oxygen content which would result in an even higher voltage... If this were the case, then it is possible that the connector is getting abnormally wet... This is only speculation, however...

So to recap, start by inspecting the connection and make sure that the it is out of the direct line of water under the vehicle. If possible, tuck it up on top of the frame rail and secure it with a large (or multiple) zip ties. The only ways an O2 sensor can get an abnormally high reading is for either the blockage of the exhaust gasses to the exhaust side of the sensor or an increase in oxygen to the outside portion of the sensor or an internal/external wiring fault. I would find it very hard to believe that water would cause an increase in the O2 count on the outside portion. That doesn't mean that water isn't getting into the sensor and shorting something out inside it. I would have to put it on my scan tool to monitor the output from that sensor to see what was going on...

Good Luck and hope my post wasn't too long...

 

I wanted to add to this thread.

I got the 138 on my 95 Jimmy. So, I replaced the sensor. About 10 miles later it pops again. Of all times while I am driving to the bank with the new owner to get the cash.

Anyways, I crawled back under the car and inspected the connector. The pin that worked the heater was hella corroded. Then I looked at the old sensor I had replaced it was really corroded also.

So, I went to NAPA and bought a four pin weatherpack connector. Cut of the stock connector and the new o2 sensor's connector and hooked it all up.

So far 120 miles on it and no codes. I think I fixed it! And it is mute point since it is sold and gone :P

So, check for corrosion in the connector.

James

 

Corrosion is always bad for an electrical connection. Using some electrical contact cleaner and a small electronics cleaning brush should remove any harmful corrosion from the connection. Once it is clean, just plug it back up. I would not recommend using any dielectric grease in the O2 connection. I have had that cause problems before as well.

 

i have a 96 Lt blazer have the same problem it does it when it rains or i drive threw puddles its a o2 sensor i changed two of them my truck has 4 but the other two i dident change one has a fray or the wire cotating split or sumthing i have yet to replace them just thought id add some in put from someone who has had the same prob thanks