j4bs4209333

Hi I am hoping someone that has had a similar problem can help me out. I just picked up a 99 WJ 4.7L with 190k. The previous owner had it for 2 years and never bothered to do any maintenance to it. At first I was getting codes for all the O2 sensors and I was also getting a code for running lean. It was horrible at idle and would die if I didn't throw it in N at a light. The exhaust smelled like it was burning too much fuel also. I found a post online advising to check the O2's to make sure fluid didn't drip on them. The 3 sensors that are more toward the passenger's side were all fine. The one that's more toward the driver's side was soaked with oil because the oil filter seems to be leaking. I unplugged that sensor and left it unplugged. Now it idles fine, no more horrible exhaust smell and the gas mileage is a little bit better (still horrible though) but I am now getting 7 different codes. I am getting:

P0132 Oxygen Sensor Circuit High Voltage (Bank1, Sensor1)
P0141 Oxygen O2 Sensor Heater Circuit Malfunction (Bank1, Sensor2)
P0161 Oxygen O2 Sensor Circuit Low Voltage (Bank2, Sensor2)
P0138 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)
P0158 Oxygen Sensor Circuit High Voltage (Bank 2 Sensor 2)

and 2 pending

P0135 Oxygen O2 Sensor Heater Circuit Malfunction (Bank1, Sensor1)
P0155 Oxygen O2 Sensor Heater Circuit Malfunction (Bank2, Sensor1)

I am just wondering if it's possible to have 4 bad sensors all at once, or could it be a wiring problem? I don't want to play the trial and error game if I don't have to. If anyone can give me some advise I would appreciate it. Thanks

KF2M

Considering that the previous owner didn't maintain the Jeep (and probably the previous owner before that), and given the mileage I would just replace all the sensors after cleaning up that oil leak you mentioned then go from there. Then again I am of the mindset that I take care of everything all at once (budget, and time permitting) so I don't spend most of my time wrenching on it the Jeep than driving it.

GI-Jeepin'

I had the same issues in my 2001 WJ with the 4.0L. There are ways to test each individual sensor, but with that many miles I would replace all 4 for the peace of mind. Besides, 4 new sensors will help your fuel mileage. I replaced all of mine with units I purchased at Rock Auto, best price I have found. I have also heard members here say to stay away from the Bosch units so I went with the NTKs, they seem pretty good so far.

Also, fix your oil filter leak.

j4bs4209333

Thanks for the advise. I'm going to order 4 new ones, I was just hoping it wasn't a wiring issue but since GI-Jeepin had the same problem and the sensors were the problem I feel better ordering them. The gas mileage is really bad, hopefully after the new sensors will pay for themselves in gas saved. Thanks for your help guys.

Michael4

Notice that they all say circuit in them, that makes me think it's a wiring problem.

GI-Jeepin'

They all say circuit because the sensor completes the circuit. Depending on what the sensor is reading determines what signal the sensor sends. Too high or too low a voltage signal will register as a problem with the PCM.

j4bs4209333

Just wanted to update this in case anyone else has the same issue. I was still unconvinced that all 4 were bad at the same time, even though the mileage was high I still thought it was weird. I grabbed the front 2 sensors out of a junkyard assuming the oil caked one was bad. After changing those 2 I still had 5 codes come back up after clearing out the MIL light. I had checked the fuses before replacing anything and because they're on the edge of the fuse box I could see that they weren't blown so I didn't bother to pull them. I took a power tester out yesterday and tested the fuses assuming maybe one of them wasn't getting power. The O2 sensor fuse was fine but there was only power on one side of the 20A fuse labeled California O2 sensors. I pulled the fuse and it wasn't blown inside but it was so corroded that the prong on one side had rotted off and was stuck inside the fuse panel. I pulled the battery cable off and stuck a mini flathead in there to clear out the broken piece and replaced the fuse. I drove it to work and then back home yesterday and 2 monitors are still not ready, but there's no pending codes so I'm sure that was the problem the whole time. Before this I would clear the MIL and within 5 minutes of driving it would come right back on again. Yesterday was the first day the it idled fine without pulsating and the exhaust finally didn't smell like burning raw fuel. Anyone else that has a problem with all 4 sensors at the same time should check both fuses before spending the money on the sensors.

Bustedback

That is some good diagnostic work. I wish more people would diagnose the problem instead of blindly throwing parts at the problem.

wildspear

Yup good deal on tracking down the issue. This is a good heads up for everyone. Just because the fuse seems good doesn't mean the whole thing is good.