O2 heater cycle won't run

imactj2004

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Okay, need some help here.

Im about $1000 and 3,000 miles into this with no solution so far.

Issue: 02 Heater Cycle test wont run —> cant pass smog

Addressed:
i have done every drive cycle test on this list, multiple times: https://smogcheckvacaville.com/chrysler-drive-cycle-odb2-readiness-monitors/
Steps taken:
- new NTK Sensors throughout
- all voltage and grounding is solid
- feeling that only remaining issue would be the PCM, I sent it in to WranglerFix and he ran the test and found no problems with PCM
basic info:
- 04 Rubicon auto
- engine all stock except for aftermarket electronic radiator fan with 210 fan switch control
- replaced battery approc 5000 miles ago which is when all drive cycles were reset. Everything clears except 02 Heater and Evap. I can pass smog in CA with one, but not two, pending tests.
 
There are two TSBs (technical service bulletins) for the 2004 that might have something to do with it not passing smog...

TSB Reference #2100905
Description: MIL (MALFUNCTION INDICATOR LAMP) ILLUMINATION FOR DTC'S (DIAGNOSTIC TROUBLE CODES) P0750, P0755, P0760, P0765, P0846, P0871 OR P0841. 2004-2005 JEEP CHEROKEE AND 2005 CHRYSLER 300/MAGNUM *SC

TSB Reference #2100804
Description: MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATION -DIAGNOSTIC TROUBLE CODE (DTC) P1776 SOLENOID SWITCH VALVE LATCHED IN LR POSITION. *MJ THIS OCTOBER 16, 2004 BULLETIN REPLACES 21-008-04 DATED JUNE 1, 2004.

You can usually Google fixes for TSB numbers like the two above...
 
There are two TSBs (technical service bulletins) for the 2004 that might have something to do with it not passing smog...

TSB Reference #2100905
Description: MIL (MALFUNCTION INDICATOR LAMP) ILLUMINATION FOR DTC'S (DIAGNOSTIC TROUBLE CODES) P0750, P0755, P0760, P0765, P0846, P0871 OR P0841. 2004-2005 JEEP CHEROKEE AND 2005 CHRYSLER 300/MAGNUM *SC

TSB Reference #2100804
Description: MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATION -DIAGNOSTIC TROUBLE CODE (DTC) P1776 SOLENOID SWITCH VALVE LATCHED IN LR POSITION. *MJ THIS OCTOBER 16, 2004 BULLETIN REPLACES 21-008-04 DATED JUNE 1, 2004.

You can usually Google fixes for TSB numbers like the two above...

thx @Jerry Bransford where can I read the full TSB for those? If Im reading correctly, the first is for a Cherokeee and C300 though.


btw - I forgot to mention that I have no CIL on and no pending codes. Scanner just say that the two monitors cant be set (02 HTR and EVAP).
 
TSB 25-001-07 describes a fix for this issue, it's described as "I/M Readiness Check Continues To Indicate OBD System Is Not Ready For I/M Testing" and typically indicates that the O2 Heater Monitor has not run. The only problem is that this TSB is supposed to apply to '05 and '06 Wranglers only (both 4 and 6 cylinder engines).

It's not unusual to hear of cases of late production run Jeeps getting parts slated for the next year's production, so it could be possible that if your '04 was a late production date perhaps it's got the '05 PDC (Power Distribution Center, a.k.a. fusebox). The fix is a minor wiring change in the PDC. I had the dealer make the change to both of my 06's many years ago because my O2 Monitors weren't running and they've been fine ever since.

It might make sense to get the TSB and check the wiring in the PDC to see if it matches the pre-fix wiring described in the TSB; if so it may make sense to make the wiring change described in the TSB. Also before making the change it might be worthwhile having the dealer check to see if the TSB description in their system has been updated to apply to some '04s.

If you can't find the TSB, send me your email and I can send you the PDF of the TSB.
 
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TSB 25-001-07 describes a fix for this issue, it's described as "I/M Readiness Check Continues To Indicate OBD System Is Not Ready For I/M Testing" and typically indicates that the O2 Heater Monitor has not run. The only problem is that this TSB is supposed to apply to '05 and '06 Wranglers only (both 4 and 6 cylinder engines).

It's not unusual to hear of cases of late production run Jeeps getting parts slated for the next year's production, so it could be possible that if your '04 was a late production date perhaps it's got the '05 PDC (Power Distribution Center, a.k.a. fusebox). The fix is a minor wiring change in the PDC. I had the dealer make the change to both of my 06's many years ago because my O2 Monitors weren't running and they've been fine ever since.

It might make sense to get the TSB and check the wiring in the PDC to see if it matches the pre-fix wiring described in the TSB; if so it may make sense to make the wiring change described in the TSB. Also before making the change it might be worthwhile having the dealer check to see if the TSB description in their system has been updated to apply to some '04s.

If you can't find the TSB, send me your email and I can send you the PDF of the TSB.

Yeah, but that's for 05-06. I'm an 04.
 
TSB 25-001-07 describes a fix for this issue, it's described as "I/M Readiness Check Continues To Indicate OBD System Is Not Ready For I/M Testing" and typically indicates that the O2 Heater Monitor has not run. The only problem is that this TSB is supposed to apply to '05 and '06 Wranglers only (both 4 and 6 cylinder engines).

It's not unusual to hear of cases of late production run Jeeps getting parts slated for the next year's production, so it could be possible that if your '04 was a late production date perhaps it's got the '05 PDC (Power Distribution Center, a.k.a. fusebox). The fix is a minor wiring change in the PDC. I had the dealer make the change to both of my 06's many years ago because my O2 Monitors weren't running and they've been fine ever since.

It might make sense to get the TSB and check the wiring in the PDC to see if it matches the pre-fix wiring described in the TSB; if so it may make sense to make the wiring change described in the TSB. Also before making the change it might be worthwhile having the dealer check to see if the TSB description in their system has been updated to apply to some '04s.

If you can't find the TSB, send me your email and I can send you the PDF of the TSB.

so, suppose I go through the steps outlined in that TSB but it turns out that its NOT the cause of my problems. Would there be any risks to my system? Obviousoy, I could “undo” the wiring fix, but wondering what risks to be aware of.
 
so, suppose I go through the steps outlined in that TSB but it turns out that its NOT the cause of my problems. Would there be any risks to my system? Obviousoy, I could “undo” the wiring fix, but wondering what risks to be aware of.

Before doing it, I would find out if the TSB applies to your 2004. You might have other issues going on. (assume nothing)
 
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Still chasing this issue. Connected with someone on a FB user group who suggested putting a bung-spacer on sensor 1/1, which I've done and still haven't had any success.

Now about to start troubleshooting the full circuit and stumbled across this bit of info in the TSM which peaked my curiosity. Anyone have any experience with a fualty BTS? Before I pull the battery and look at it, I'm just wondering what I should be looking for beyond obvious signs of faulty wiring.

Screen Shot 2023-03-05 at 2.09.29 PM.png
 
Still chasing this issue. Connected with someone on a FB user group who suggested putting a bung-spacer on sensor 1/1, which I've done and still haven't had any success.

Now about to start troubleshooting the full circuit and stumbled across this bit of info in the TSM which peaked my curiosity. Anyone have any experience with a fualty BTS? Before I pull the battery and look at it, I'm just wondering what I should be looking for beyond obvious signs of faulty wiring.

View attachment 405112

I believe there have been posts on having a faulty BTS before. I’d go a google search on that if you haven’t yet. I’d try to help more but I’m sucked in on my own stuff right now.

Maybe research to find more on the general architecture of what all ties the system you are having issues with. If the BTS was faulty would that cause issues with the evap as well? And would there be codes for a bad BTS or if the BTS doesn’t provide proper input to the heater or LDP? Maybe see what other systems might tie in that way u aren’t feeling lost if u confirm the issue is not BTS related.

Best of luck man
 
Last edited:
As a test.... measure what your electrical system charging voltage is when you first start the Jeep and what is the voltage after operating for about 10-15 minutes ? The charging voltage should decrease....
The BTS is a 1" round disc inset into the battery tray.
 
As a test.... measure what your electrical system charging voltage is when you first start the Jeep and what is the voltage after operating for about 10-15 minutes ? The charging voltage should decrease....
The BTS is a 1" round disc inset into the battery tray.

to clarify: measure where? Just at the dash? or via OBD? or probe somewhere?
 
to clarify: measure where? Just at the dash? or via OBD? or probe somewhere?

Sorry….
I should have been clearer….
You can look at the instrument cluster voltage/charging gauge OR measure the voltage across the battery terminals after startup and compare after the engine has operated for about 10-15 minutes. The voltage should decrease as the engine compartment and battery warm up.
 
Okay, need some help here.

Im about $1000 and 3,000 miles into this with no solution so far.

Issue: 02 Heater Cycle test wont run —> cant pass smog

Addressed:
i have done every drive cycle test on this list, multiple times: https://smogcheckvacaville.com/chrysler-drive-cycle-odb2-readiness-monitors/
Steps taken:
- new NTK Sensors throughout
- all voltage and grounding is solid
- feeling that only remaining issue would be the PCM, I sent it in to WranglerFix and he ran the test and found no problems with PCM
basic info:
- 04 Rubicon auto
- engine all stock except for aftermarket electronic radiator fan with 210 fan switch control
- replaced battery approc 5000 miles ago which is when all drive cycles were reset. Everything clears except 02 Heater and Evap. I can pass smog in CA with one, but not two, pending tests.

Maybe let's go back to the beginning.

Have you confirmed that you do not have any engine codes?

Have you confirmed that all of your o2 sensors are reading correctly via live data?

Have you looked at the heater circuit in the FSM to see how many potential inputs there are from other systems for running the Heater cycle operation.

Have you checked to ensure there are no pushed pins or corrosion at the PCM connectors or from any other system inputs that tie into this?

Have you used a multimeter to test that your wiring is good to the o2 sensors?

Have you tried a different PCM to see if the symptoms still occur?

Just spitballing here, hopefully this helps.
 
Maybe let's go back to the beginning.

Have you confirmed that you do not have any engine codes?

Have you confirmed that all of your o2 sensors are reading correctly via live data?

Have you looked at the heater circuit in the FSM to see how many potential inputs there are from other systems for running the Heater cycle operation.

Have you checked to ensure there are no pushed pins or corrosion at the PCM connectors or from any other system inputs that tie into this?

Have you used a multimeter to test that your wiring is good to the o2 sensors?

Have you tried a different PCM to see if the symptoms still occur?

Just spitballing here, hopefully this helps.

Those questions you posted were answered in the OP previous responses including sending the ECU to Wraglerfix for evaluation.
 
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Sorry….
I should have been clearer….
You can look at the instrument cluster voltage/charging gauge OR measure the voltage across the battery terminals after startup and compare after the engine has operated for about 10-15 minutes. The voltage should decrease as the engine compartment and battery warm up.

so, just looking at the instrument cluster - voltage increases from about 10-ish with engine off to 14-ish after running.
 
Those questions you posted were answered in the OP previous responses including sending the ECU to Wraglerfix for evaluation.

Don't rule out double-checking your work if you don't find the issue elsewhere. (that's all I'm getting at)