Heater circuit low for all O2 sensors?

Tiny
NOAH.B.111
  • MEMBER
  • 2005 CHRYSLER 300
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 154,000 MILES
Recently purchased this car broke down as a project to fix up myself, the only codes it’s showing is the heater circuit low for all 4 O2 sensors. I replaced the sensors, and the same codes are still present after clearing. I have tested for voltage, done pin to pin test for continuity, everything seems to check out. I read the wiring diagrams and the upstream and downstream sensors look to be completely separate including the ground location. There also doesn’t seem to be any fuses associated with the sensors.

The car stalls out usually within a minute of running and sometimes will level out and run. I have read the fuel trim and when it first started it starts at 0 and just slowly falls to -32 and shuts off. I tried unplugging the sensors to see if it would run and it did for a couple days then started stalling again, when looking at the fuel trim it was now doing the exact opposite and was a positive fuel trim and slowly stalled out. With the sensors plugged back in it switched back to a negative fuel trim. The MAP reading also seems a little low it reads about 11” at idle

Before I drop the money on a new PCM is there anything else that could cause this issue? And if I do need to go the PCM route, what is the best option? Junkyard, pre-programmed, or should I just take it to a mechanic?
Wednesday, July 5th, 2023 AT 5:22 PM

14 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

It sounds like you have a live data scan tool. With the engine running, what voltages are you seeing at the sensors? If you haven't checked, here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

If you are at a -32% STFT (operating temperature), it's getting way too much fuel. Have you checked to see if the fuel pressure is within spec?

Let me know the codes you are getting so I can dig a little deeper into the possible causes.

Take care,

Joe
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Thursday, July 6th, 2023 AT 9:36 PM
Tiny
NOAH.B.111
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The codes are P0031, P0037, P0051, P0057. I have checked the voltages multiple times and they are usually between.5 and.8v (depending on if the car stays running). I have not been able to check the fuel pressure because I don’t have a tester, I tried one but the car doesn’t have a shrader valve to connect to.
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Friday, July 7th, 2023 AT 1:52 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

When you have a low voltage issue like this, either the sensor is bad, you have a short to ground, or the PCM is failing.

Did all of these codes show up at the same time? Are you comfortable performing diagnostics specific to the codes? If you are, I attached the diagnostics for the P0031. The diagnostics for the other codes are the same but different pin connectors are checked.

Let me know.

Joe

See pics below.
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Friday, July 7th, 2023 AT 7:26 PM
Tiny
NOAH.B.111
  • MEMBER
  • 12 POSTS
Thank you for the diagnostics, the only thing I’m stuck on is the testing for the short to ground. It says to disconnect the PCM harness connectors and to test at the o2 sensor harness which I did, but the multimeter isn’t registering any resistance at the harness connector. If I probe the heater wire at the PCM harness (with the sensor plugged in) it reads 4.5 ohms. That’s less than 5 would that indicate a short to ground. Also, how would that work considering the upstream and downstream sensors have different grounds? If it helps, I probed other non-related wires as well and they were all over 10 ohms.
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Saturday, July 8th, 2023 AT 12:31 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

When you checked for resistance with the sensor unplugged, did you go between the PCM, and the sensor plug to check for resistance? With that test, you are testing the wire only. Also, when you tested and found no resistance, what was listed on the DMM?

Let me know.

Joe
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Saturday, July 8th, 2023 AT 9:57 PM
Tiny
NOAH.B.111
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  • 12 POSTS
I tested the resistance between the heater circuit wire in the sensor harness and ground (with PCM harnesses disconnected) the multimeter read O.L.
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Saturday, July 8th, 2023 AT 10:08 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

OL indicates an open loop, meaning there is no connection. That is odd. If you are going from one end to the other, there should be a connection or continuity.

You know the DMM better than me. On yours, is that what the OL stands for? I ask because there are different manufacturers, and they all have different ideas. LOL

Joe
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Saturday, July 8th, 2023 AT 10:15 PM
Tiny
NOAH.B.111
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Yes, I believe that is what it stands for on mine. If I test the heater wire from PCM harness to the sensor harness it does read 0.00 ohms.

It seems odd to me they say to disconnect the PCM then test the resistance from the sensor side to a ground?
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Saturday, July 8th, 2023 AT 10:44 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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They want to make sure the wire itself isn't faulty. It sounds like you may have found the issue. Let me know if you get it resolved.

Take care,

Joe
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Sunday, July 9th, 2023 AT 12:05 AM
Tiny
NOAH.B.111
  • MEMBER
  • 12 POSTS
So, If 0 means good continuity then the wire is fine, and it would be a faulty PCM?

Also, just found out the O.L when measuring resistance actually stands for over limit, of what the multimeter can read.
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Sunday, July 9th, 2023 AT 12:15 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I never heard that one before. As far as the issue, if the wiring and everything other checks good, then unfortunately, it sounds like the PCM has failed.

Do you plan to replace it?

Joe
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Sunday, July 9th, 2023 AT 6:28 PM
Tiny
NOAH.B.111
  • MEMBER
  • 12 POSTS
Yes, I will replace it, what would be the best option for that? Do the pre-programmed ones work?
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Sunday, July 9th, 2023 AT 7:36 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

There are sites online that offer remanufactured ones. They get information from you and program it before sending it. At that point, you install it, and it should not need anything else.

I have used different sites in the past and it has always worked.

Let me know.

Joe
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Monday, July 10th, 2023 AT 8:56 PM
Tiny
NOAH.B.111
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Awesome, thanks for all your help! I will keep you updated when I get a new PCM.
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Tuesday, July 11th, 2023 AT 12:25 PM

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