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Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3404
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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Dodge Ram 1500: I have a 2004 dodge ram1500 5.7l hemi I had

Customer Question

I have a 2004 dodge ram1500 5.7l hemi I had to stop hard one day and it started running rough. then stopped and was running okay. then after a day or so started running rough again and gave a po300 code so i changed plugs wires checked all coil packs fuel pressure and cleaned throttle body and pulled neg battery cable to reset everything. ran great for a day but gave me a po132 code cleared code when i got home. started it this morning running rough again gave a po172 code this time.cleared code still running rough spitting and sputtering after driving it for a bit it got better but i can tell its still sputters a little.
Submitted: 2 years ago.
Category: Dodge
Expert:  Dodgerench replied 2 years ago.
Hi, my name is Ed. Welcome to JustAnswer!.
Your symptoms make me wonder if the upstream oxygen sensor heater has lost capacity. An under-heated 02 sensor in this location will leave oxygen sensor voltages high, possibly tricking the PCM into believing your engine is running rich. The reaction would be to pump down fuel trim, removing up to 70% of originally calculated fuel delivery at the injectors in an attempt to correct the (perceived) condition.
I'd be suspicious of the upstream 02 sensor, which my information shows to be a single unit, located just behind the convergence of the two exhaust streams and before the catalytic converter.
The 02 sensor heater is internal to the sensor and will cause a code to set if the circuit becomes completely open, but instances where the heater is still connected... but reduced in capacity... may not trip the code and the performance-saving default that it would provide. Instead, you've got a fuel system that becomes convinced that it's running rich all the time, driving fuel adaptives heavily toward removing fuel and this is likely the reason why the truck runs OK for a brief time after you've cleared memory, until the adaptives are corrupted again.
One piece of advice in choosing an 02 sensor involves the manufacturer. You need to stick with either an OEM Mopar unit (safest) or an NGK or NKK manufacturer in order to maintain the delicate balance of what's looked for in the circuit (by the PCM). A sensor with an out-of-spec impedance often looks like an 02 sensor that's already heated to the PCM, which then tapers off its feed to the sensor, leaving it cold. Yeah, it's still broken.
Without an actual 02 sensor heater circuit... WITH a code for high voltage and running rich... I'd give the probability of a bad upstream 02 sensor about 90% chance of fixing the whole she-bang.
Let me know what you find and if you have any questions or problems. I'll be glad to help.
Thanks for writing!

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