Tx9h6e4cuda

My 2001 Cherokee is missing the after cat 02 sensor and wiring. The old owner had hacked my jeep up pretty well. I'm wondering if you could tell me where the wiring goes to from the 02 sensor and where it connects to the underbody harness. My check engine light doesn't work but my MPG is really bad. Please help and pics would be really helpful.

x91evo

the O2 sensor after the cat does nothing but tell the PCM if the cat is working properly or not

x91evo

Personally its better without it, you wont fail emissions if you get a bad cat

CCKen

Incorrect.

Here's an article from a Dodge Ram website that will help you understand the function of the downstream O2S, and its roll in fuel economy.

Upstream Oxygen Sensor Goal Voltage

From Star Center News #5, February 2000 - tests for those who have access to OBD II or OBD III code readers.

Since the introduction of OBDII with both upstream and downstream O2 sensors, the downstream O2 sensor has been used to evaluate catalytic converter operation and to control converter efficiency.

When looking at the upstream goal voltage, it should fluctuate above and below the normal center (.4 to .6 volts) based upon what the downstream O2 sensor is reading. The vehicle should be driven through all speed ranges when checking goal voltage. If the goal stays high or low all the time, a thorough check of the downstream oxygen sensor should be made. Be sure you check the sensor, wiring harness, connectors, catalytic converter, and inspect for exhaust leaks.

Although a MIL lamp may not be illuminated, there are instances when the downstream O2 sensor goal voltage is out of range, causing driveability problems or low fuel economy.

If the downstream O2 sensor tends to stay below center all the time, the PCM will adjust the goal voltage higher in an efforet to correct the low O2 readings of the downstream sensor. This can result in low fuel mileage.
If the downstream O2 sensor has a tendancy to stay above center, the PCM will set a low goal voltage which results in a lean fuel mix which can cause the engine to run hotter and aggravate a spark knock condition.

Sometimes a service technician will reset the PCM and take it for a test drive. The PCM does a recalibration after the reset, and the probelm may go away until the PCM has completed a relearn of the system and then begins to attempt to correct for the downstream sensor error. If the symptoms reappear after several days of driving after a service is performed, check the downstream O2 sensor, the exhaust system, the wiring, and the catalytic converter. Note: a worn out catalytic converter can produce symptoms similar to a bad downstream O2 sensor.

CCKen

Do you have a Federal Emissions O2S set up (two O2s's) or a California Emissions set up (four O2S's)?

salad

For reference CCKen the 2000 XJ FSM explicitly states that downstream O2s are involved in setting fuel trim as well.

Tx9h6e4cuda

I have federal emissions, so where does the wiring go.

CCKen

Exactly.

All OBD II XJ's do this.

CCKen

Do you have a Catalytic Converter?

Refer to Figure 14 in post #5, there should be a bung in the exhaust pipe after the Cat.

Just above that bung there should be a bracket that secures the O2S connectors (see figure 14). Some people either lose the bracket or intensionally leave it off (bad idea). The O2S connector and the body harness connector for the O2S should be black. See if you can find the body harness tucked away somewhere.

If you can find the body harness connector it's a matter of buying a new O2S* (Use NTK O2S #23099) and connecting it up and securing it to the bracket. If the bracket is missing there is a threaded hole in the frame that holds the bracket in place. It uses a 6 MM bolt (as I recall). Get a suitable clamp and secure the connectors in place with a bolt.

If the body harness connector is missing get back to this thread. You'll need to get a connector from the junk yard (or elsewhere) and splice it in.

Replace the upstream O2S as well (NTK #23506). Both are available from Rockauto .com.

Tx9h6e4cuda

Ok this is what the deal is, I bought my Jeep from a 17 year old moron who never should touch a car again. He hacked the exhaust directly off after the cat (taking the 02 sensor with it). He bolted up a glass pack and called it good. I bought the Jeep I sourced another exhaust system from a 2000 XJ. I installed it and it had the second 02 in the exhaust but my truck does not have the wiring anywhere. I've looked at the wiring that goes to the transmission (nearest harness to exhaust) and nothing there for a connector or loose harness or wires at all. I'm afraid he cut the 02 wiring off at the main harness wherever it goes. I understand what the downstream 02 sensor does, where the sensor goes, and etc.

What I am looking for is someone to please climb under their 2000-2001 Cherokee and trace the rear 02 harness to where it meets the main harness. I know the moron previous owner did something bad here I just need to find out where he did it but I don't have another example near me to compare. A pic would be awesome too......

Also my check engine light doesn't work, it doesn't do test mode when the key is turned to accessories or even in the factory test mode. I replaced the bulb and nothing still.

Thanks for any help.

CCKen

Maybe this will help:

Moncheche

He must have owned the suburban I bought last year. He couldn't figure out why it wouldn't run right.

Once I replaced the O2 sensor, the engine smoothed right out.

The downstream sensor is a crucial variable in the puter's calculations.

ss427ci

I have Cali emissions (4 O2) but here is a pic where the bank 2, sensor 2 connector is. You can see the gray plastic point coming through the bracket. The wiring goes up into the engine bay into a huge wire loom and not sure which direction it goes from there. Either to the second picture or to the PDC where the fuses are.

Tx9h6e4cuda

Ok I've been out of town and finally got to look at my 2001 Cherokee. Well I went under the truck and there is absoutly no harness for a 02 sensor in-between the rear cat and muffler. I noticed that there is a 02 sensor on upper side of the exhaust manifold cat and another 02 sensor below the exhaust manifold cat.

Now my question is my 2001 Federal emission Cherokee is there two or three 02 sensors?

CCKen

Look at those images of the 2001 XJ O2S configurations again. What do you have?