113Cherokee

I have codes for both O2 heater circuits. I have replaced both sensors. I have checked the fuses. I am now checking the wiring and I get a good ground on the ground circuit I also get 4 V to the sensor but I have ground on the sensor return wire is that normal? If not what could cause this?

This is on my 2000 xj

CCKen

Not to challange your ability to check fuses, but did you check fuse 10 in the Junction Block and fuse 17 in the Power Distribution Center?

Generally I don't trust eyeballing mini fuses, I just replace them.

Your 2000 XJ has two O2S heater relays in the PDC and its doubtful that both relays would go bad at the same time. Fuse 10 in the JB is power to the relay control coils in both relays, if this fuse blows both relays will be taken out. However, fuse 10 in the JB also powers the Radiator fan relay and AC Compressor Clutch relay control coils. If blown, these relays would be dead also. Fuse 10 is powered when the igniton key is in the RUN position.

Fuse 17 provides power to both upstream and down stream O2S heaters through the heater relays (when activated) from the battery bus.

I'm a bit confused as to how you are reading the wiring at the O2S's. Are you reading the O2S heater circuits (two white wires attached to the O2S). These are the heater circuit wires. One is power from fuse 17 in the PDC and the other is ground. There is no "sensor return" in these circuits.

113Cherokee

I have checked all of the fuses and relays. When I turn the key on I get 4v at the connector with the O2 disconnected. I use continuity tester to test ground circuit and got ground. But also got ground on signal return wire.

113Cherokee

Unless I am wrong i believe 2000's do not use fuse 17.

DFlintstone

I'm just learning here. 4 volts might be a little low, and no, I don't think you should read a good ground on the signal wire. Maybe monitor that grounded signal wire as you poke around a bit and jiggle things. Being the 02's are near hot stuff they tend to have issues with the wires. 12 Getten from the heater wire to the signal wire will throw a code as well.

113Cherokee

I have not seen anything wrong with the wire from what I can tell.

DFlintstone

Maybe you can't see it? Maybe monitor that grounded signal wire (with the meter), as you poke around a bit and jiggle things. My meter has a setting where it whistles when it has a ground, a handy feature it there are not two people.

salad

The O2 heater supply wires are supposed to have battery voltage on 'em. 12V with the key in RUN, 14V when the engine's going.

All of the power feeds for all of the O2s runs through connector C107 which lives just by the back of the engine. It's a black connector with two rows of 7 pins. Pop it open and check for corrosion, also you'll want to look for 12V on pins 7 and 13

DFlintstone

I think he's sayen he's getten 4 from the PCM feed, and finding the return grounded.

CCKen

113Cherokee,

Still can't figure out what you are testing and why.

You didn't say if you have Federal Emissions O2S (two O2S) or California Emssions (four O2S), nor did you state what "P" codes you had.

Anyway, here's the wiring diagrams, PDC, and JB, for the O2S circuits in your 2000 XJ.

Note that there is a fuse F17 in the PDC.

At this point there is no sense in trying to check O2S sensor outputs because you have O2S heater issues (your description in post #1), besides you need to check O2S sensor outputs by back-probing the O2S connnectors while they are attached and the engine is running.

It appears as though you have installed new O2 sensors, so I would think the O2S heater [failure(s)] originate from the circuit(s) that feed the O2S heaters. However, you can check those new O2S heaters by disconnecting the body harness connector from the O2S connector, and using an Ohmmeter, probe between the O2S connector pins for both White wires. You should see around 6 Ohms at room temperature. If the heater elements are not defective then you need to check the power feed to the O2S heaters.

A preliminary physical check of the O2S heater ground points and the O2S wiring harnesses in the engine bay should be conducted.

1. The O2S heaters ground point (G101) is on the right side of the engine, near the alternator (same place as the battery ground (-) cable is attached to the engine). THere are other circuits ground here as well. Check the ring terminals at this ground point (two studs) for security of attachment, then remove them and check for corrosion, clean if required then reattach.

2. Check the O2S haness loom as it passes over the intake manifold for chafing through to the wires.

With all fuses good (replaced) and known good relays are installed - check for battery voltage to the O2S heaters (refer to diagram(s).

1. Detach the O2S body harness connector from the O2S connector,

2. Turn the ignition switch to RUN,

3. Upstream O2S: Using a Voltmeter, probe the body harness connector. Meter (+) probe to the pin for the Dark Green wire and the (-) probe to the pin for the Black wire. You should see battery voltage. If not move (-) probe to a good ground on the engine. If you see battery voltage now, the ground circuit wire (Black) is open between the connector and ground G101. If still no battery voltage there is a bad fuse, relay, or an open power wire.

4. Downstream O2S: Same as the Upstream except the power feed wire is Violet/Orange tracer wire.







JB:



PDC:

113Cherokee

This is exactly what I am getting

DFlintstone

If you post your actual codes it might be helpful to someone more in the know than me! I'd hook up a meter and mess with the wires to see if I can find where that's grounding.

113Cherokee

I have no voltage here what does this mean?

salad

Relays aren't sending power or you have some sort of wiring issue. Refer to the pics that CCKen posted

113Cherokee

I have no battery power at 16 and 11 at both relays on both. O2 relays