Hello I am new to the forum and new to mechanic work and still learning. My 1999 Jeep cherokee in-line six cylinder 4.0L engine was not idling well so I mostly tuned it up (plugs, wires, rotor, distributor cap,) and since the problem was worse on hot days and only happened at operating temp I put in a CTS and MAT sensor for good measure. Problem solved. But ... last night we had a really heavy rain and I hit a BIG puddle. the engine started sputtering again but stopped and worked fine when it dried. With "check engine" light on I went to AutoZone and they plugged in and got this message on the on board diagnostic: "O2 sensor heater bank 1 sensor 2 shorted to voltage". I looked at both O2 sensors and they look OK. The wires go into a harness and the only place I could see that might have got wet is at the sensors. Question: what is "heater bank" and how would I correct this? Thanks in advance. Neven

 

I almost bet it said "heater circuit", "bank 1", "sensor 2". The O2 sensors are electrically heated so they will quickly reach operating temp (+/-650F) and signal the ECM.

 

It's not a heater bank. The code is O2 sensor heater, bank one, sensor two shorted to voltage. If this were a V style engine you have bank one and bank two, it refers to the cylinder banks of the engine. Your code is telling you the O2 heater cicuit is shorted to voltage on the down stream O2 sensor. It could be the sensor or the wiring.

 

I let the girl at AutoZone read the result to me so you guys are right. I have a very basic understanding of how the jeep works but need a LOT of reading up on the technical language. This NEVER happens unless I hit a puddle (yep, tried it again). Would I replace the downstream O2 sensor or should I look somewhere else (harness??) for where this water could be hitting and shorting? BTW I suspect my catalytic converter may be partly clogged. Could splashing affect this? Actually since the tune up it runs great except it hates puddles (staying out of the creek for now) Thanks!!

 

Disconnect the connectors @ the O2 sensors, clean and dry them, then reassemble with a little dielectric grease. Then carefully go over the wiring, looking for any breaks in the insulation, or any other sort of damage and fix as appropriate. I bet that takes care of the problem.