All the 02 heater codes! - JeepForum.com
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post #1 of 14 Old 08-17-2020, 01:58 PM Thread Starter
thechainrule
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All the 02 heater codes!

So I'm trying to troubleshoot why my CEL is on. I just pulled the codes in my WJ and was given a code for each 02 sensor heater circuit:
P0135
P0141
P0155
P0161


I have the 50 state exhaust setup on my 4.0 stroker with the precats, so I have 4 O2 sensors and all are throwing a code. Whats worse is that I just had these sensors replaced not too long ago so I am thinking that it might be something outside of the sensors. I checked the the fuse (#16) in the engine compartment and its fine. The jeep overall runs fine. I still get 20ish mpg on the highway. The mechanic who installed these left a lot of the jacketed wire exposed pretty close to the exhaust but I don't see any sign of melting. Any ideas?

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post #2 of 14 Old 08-17-2020, 02:59 PM
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tell is what year WJ. Will help with wiring details.
do you know what brand sensors were used, recommended is NTK or fro jeep dealer, Aftermarket sensors are 'lacking'.

Do you have a scanner?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 14 Old 08-17-2020, 05:47 PM Thread Starter
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I have a 2000 WJ 4.0L laredo. 204,000 miles.

I think they are denso, would need to double check again when I get home. I have been using the Torque app on my phone to pull codes and such but not a proper scanner.
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post #4 of 14 Old 08-19-2020, 02:16 PM Thread Starter
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I'm at a loss here trying to sort this out, anyone have any ideas before I purchase 4 more 02 sensors?
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post #5 of 14 Old 08-19-2020, 02:50 PM
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just saw this post - now that we know what MY let me get a diagram of sensor wiring...

Give me a little time.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 14 Old 08-19-2020, 02:57 PM
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details check the relays and their circuits - SORRY no time to walk you thru this. hopefully a colleague can help right now...
Attached Files
File Type: pdf 93ZJ PCM pinout.pdf (164.2 KB, 2 views)
File Type: pdf 00WJ o2 sensors.pdf (210.8 KB, 9 views)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #7 of 14 Old 08-19-2020, 07:14 PM
Wabatuckian
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Hello,

First thing: What brand O2 sensors? I was throwing heater codes with two aftermarket brands I tried, the last being Bosch. Got some Mopar, and folks are right when they say they're needed.

Second thing: Check the G104 grounding point for corrosion.

Third thing: Check heater circuit. I use a pigtail from a bad O2 sensor and a digital multimeter. Pinout from PCM should work, but I like to make sure signal is getting to the O2 sensors.

Josh
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post #8 of 14 Old 08-19-2020, 09:35 PM
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A little more info from my ground write-up and you can see the G104 ground with wires on the driver's side engine block in the in the last 2 photos of the below section.

https://www.jeepforum.com/forum/f310.../#post39199354

Granted this is on my 04 4.7 but believe the 4.0 G104 ground is the same location.* Easiest to get to from underneath and jack up the body behind the driver's side front tire while leaving the axle down.

My 04 4.7 Fed emissions came with 4 Denso o2 sensors when I bought it about 8 years ago and replaced them with the same Denso sensors while no o2 codes.

* Edit: I may stand corrected and look for the G104 ground around the oil dipstick tube support bracket on the right side engine block towards the rear on the 4.0. Not a bad idea to clean G103 (PCM grounds) behind the motor mount on the right side block too.
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2004 4.7L WJ Limited, 96 4.0 ZJ


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post #9 of 14 Old 08-20-2020, 12:06 AM
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details
Attached Files
File Type: pdf troubletree.pdf (66.8 KB, 6 views)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 14 Old 08-21-2020, 07:56 AM Thread Starter
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Quote:
Originally Posted by Wabatuckian View Post
Hello,

First thing: What brand O2 sensors? I was throwing heater codes with two aftermarket brands I tried, the last being Bosch. Got some Mopar, and folks are right when they say they're needed.

Second thing: Check the G104 grounding point for corrosion.

Third thing: Check heater circuit. I use a pigtail from a bad O2 sensor and a digital multimeter. Pinout from PCM should work, but I like to make sure signal is getting to the O2 sensors.

Josh
I'll have to take a look at the sensor itself again later tonight to confirm, but I am willing to bet they are not genuine mopar sensors. While I'm at it I will inspect those grounds. Given that all 4 sensors are bad simultaneously, I hope this is it!

For point 3 what am I looking for on the gauge? Is it a 0-5 volt sensor or am I looking for 12V and amperage across the heater circuit. Im struggling to follow that diagram right now.
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post #11 of 14 Old 08-21-2020, 09:14 AM
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I like your plan - checking the o2 sensor heater, you will want to look at the resistance - I found the aftermarket sensors did not have the specified resistance, also resistance to ground, and the actual voltage (battery) being delivered to heaters.

IIRC you have the OEM manual with the wiring diagrams? let us know.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 14 Old 08-21-2020, 01:46 PM
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Quote:
Originally Posted by thechainrule View Post
I'll have to take a look at the sensor itself again later tonight to confirm, but I am willing to bet they are not genuine mopar sensors. While I'm at it I will inspect those grounds. Given that all 4 sensors are bad simultaneously, I hope this is it!

For point 3 what am I looking for on the gauge? Is it a 0-5 volt sensor or am I looking for 12V and amperage across the heater circuit. Im struggling to follow that diagram right now.
The O2 sensor heating element draws a full 12v, pulse width modulated from the PCM.

In fact, this page on motor.com claims you can test the circuit with a light bulb. I've never heard of that, but I guess it makes sense, and would make a nifty permanent part of a diagnostic kit. (In the dark ages when I practiced auto tech professionally for a bit, we made all sorts of nifty diagnostic tools. Gotta remember, OBDII had just come out the year I started that profession. I don't know if it's still a thing for professional techs to make tools like this.)

Josh
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post #13 of 14 Old 09-21-2020, 04:43 PM Thread Starter
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Right, so I finally have an update.

Went under the hood this weekend and tried to clean up the G103 and G104 codes per the article posted by Uniblurb and I think I got half of the equation right. On my 4.0 block I found the 103 in the middle with some sort of relay box attached to the ground, the G103 ground strap was there but had seen better days. I believe 104 was underneath the last coil pack and had two things attached to it plus the trace of a completely eroded ground strap. Unfortunately it was just the strap as both of the crimps on the end were gone, and therein lies the problem for me. Where does the non-engine side of the ground actually go?

Foolishly, I attempted to wire G103 and G104 together in a Y adapter. That did not work well so I have reverted back to a new ground strap on G103 and nothing on G104 until I can find where on the body it belongs.

Y Adapter for grounds 103 & 104. Do not do this!




Prepping g103 ground location with sandpaper






Hilarious leftovers of og grounds 103 & 104.
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post #14 of 14 Old 09-21-2020, 09:16 PM Thread Starter
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Quote:
Originally Posted by Uniblurb View Post
I may stand corrected and look for the G104 ground around the oil dipstick tube support bracket on the right side engine block towards the rear on the 4.0. Not a bad idea to clean G103 (PCM grounds) behind the motor mount on the right side block too.
I was able to clean up G103 and install a brand new ground strap. Need to find the chassis ground for G104 so that I can install a new strap on that circuit too but I cant find the grounding post on the chassis.
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