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Ypahihi 12-09-2011 11:29 PM

Another O2 Sensor Question
Was under the bonnet yesterday and noticed that my 2000 GC limited 4.7 doesn't have front or rear O2 sensor relays.
I also have a 4.7 2000 GC Laredo for spare parts which does have the relays and I'm kinda lost as to whether the limited is functioning optimally?
I pulled the relays from the Laredo and attempted to plug them into the Limited but there is nothing for them to seat into.

The question at hand is:
Should the GC Limited have relays or not and will it make a difference to my fuel economy? :confused:


Frango100 12-10-2011 06:18 AM

Re: Another O2 Sensor Question
Depending on the emissions package the jeep has, the O2 heater elements are fed by either the ASD relay, or by 2 separate relays in the PDC. My Lmtd also doesnīt have the 2 separate relays. So no worry, the system should work ok as it is now.

PeterB16 12-10-2011 08:55 AM

Re: Another O2 Sensor Question

Check that out. There is a diagram showing the two different emission systems.

Frango100 12-10-2011 10:36 AM

Re: Another O2 Sensor Question
Looking into the PDC of my jeep, i saw a " rear oxygen sensor" relay (strange, i always thought that i didnīt had any O2 heater relay). Also the wiring manual is showing both downstream sensor heaters are switched via one relay (by the PCM) and both upstream sensor heaters are switched directly by the PCM. I canīt find any reference in the wiring manual of 2 heater relays.
But if for whatever reason the O2 heater(s) wonīt work, the PCM will control the fuel delivery in open loop (= not using the O2 sensors for fine tuning) and a DTC will be set after some time.

Ypahihi 12-10-2011 12:10 PM

Re: Another O2 Sensor Question
Thanks Frank,

Apart from thinking that there was something seriously missing, I was kinda contemplating swapping the PDC's over (providing the required wiring was there) to see if it made a difference.
Maybe I won't at this stage. No need to fix something that ain't broke

Frango100 12-10-2011 05:40 PM

Re: Another O2 Sensor Question
So are you sure that your jeep doesn't have the rear O2 heater relay? If it doesn't, then probably it also doesn't have the downstream O2 sensors?

Ypahihi 12-11-2011 05:12 PM

Re: Another O2 Sensor Question
The down and upstream relays are definitely not there but I have followed where the sensors should be and they are both attached as per the diagram.
Just as an exercise I'll dismantle the PDC on the Laredo to see the wiring loom and will compare it against the Limited.
If all is there and I am able to swap them out will I need to make adjustment to the computer??

Frango100 12-11-2011 05:46 PM

Re: Another O2 Sensor Question
You say that both sensors are there, so you only have 2 sensors? If they are both upstream sensors, then there should be no relay.

Ypahihi 12-15-2011 12:41 AM

Re: Another O2 Sensor Question
5 Attachment(s)
I have taken pictures of what's on the Laredo and on the Limited for comparison.
First 2 photos are from the Laredo (used for spare parts) which I assume is the Californian emission package
Attachment 10861

Attachment 10862

And 3 photos taken from the Limited and have concluded that this is the Federal emission package
Attachment 10854

Attachment 10855

Attachment 10856

So I think I can let this rest

Frango100 12-15-2011 06:28 PM

Re: Another O2 Sensor Question
Yeh, donīt repair something what aint broken.

Me Fix 12-16-2011 08:53 AM

Re: Another O2 Sensor Question
Other than the different wiring packages, is there something going on to make you think there is something wrong with your O2 sensors, like poor milage, stinky exhaust, rough idle or anything else that might come from your system not going into closed loop. Per Frango, it sounds like you just have two different wiring packages, maybe because of different emissions systems that might have been built into the Jeep to meet the requirements of the state the Jeep was to be sold in. It can be challenging to sometimes understand what you have per the shop manuals because in many cases the manuals cover many different systems.

Ypahihi 12-18-2011 01:57 AM

Re: Another O2 Sensor Question
Correct, it can be bewildering at times especially if the attention span just isn't there :)

Okay, I purchased the jeep and drove Sydney to Adelaide, then Adelaide, Alice Springs to Darwin in a 54 hour period covering some 4500kms and got to see what the vehicle was capable of.
10 fuel stops with 4 of those being top ups as precautions (due to location) to make scheduled refills. Fuel economy 620kms + per tank.

On arrival I had serviced Jeep at a garage (not stealership) in Darwin.
Economy is down (yes, town running will do it) to 400kms per tank. Have started driving to old fishing spots and average 310km round trips for the day and economy still poor (430kms).
Have started looking for possible problems, but it doesn't help if 'spares' jeep has a different o2 sensor for comparison sakes.
GC isn't idling rough, I did have the problem with the cooling system which seems to have been fixed and the only thing I have noticed is that on first start up of the day there is an over fueling smell of fuel which dissipates after 10 minutes or so.
After the service it really hasn't been the same. Garage indicated that they hadn't played with fuel system, but hadn't really all that much experience with Jeeps to begin with.

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