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2005 Dodge Ram 1500 5.7L HEMI Persistent P0171 & P0174 OBD2 Codes - Long-Term Lean Mix Issue

Model: 2005 Dodge Ram 1500 Fault Code: P0171 Posted: 2017-07-28 20:55

I own a 2005 Dodge Ram 1500 with a 5.7L HEMI engine and have been experiencing persistent OBD2 trouble codes P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2) for over a year. After previously resolving the issue by replacing the EGR valve, MAF sensor, and a fuel vapor recirculation vacuum line, I was able to pass smog inspections. However, the lean codes have returned consistently. I've thoroughly inspected for vacuum leaks with no obvious sources found. While I suspect clogged injectors or a failing fuel filter, the truck runs smoothly under all conditions—no hesitation at idle or during acceleration—even with a 12-inch lift and 39-inch tires. The symptoms only appear when the engine is warm and idling for several minutes. If I start driving immediately after turning on the key and then shut it off, no codes appear. The issue manifests specifically under steady-idle conditions after the engine has warmed up. I'm looking for guidance on what to check next—especially given that all drivetrain components remain stock except for a CA-legal cold air intake, throttle body spacer, and exhaust modifications (including possibly upgraded piping). Any insights into potential root causes or diagnostic steps would be greatly appreciated?

Related fault codes

P0171P0174

Comments (4)

Anonymous 2017-07-29 07:06

Do you have access to a dedicated OBD2 scanner? If so, please share live data readings—such as ECT, MAP sensor values, fuel trim percentages, and oxygen sensor voltages. This helps identify whether the issue is in the air-fuel mixture or downstream components. Is your truck stock configuration? Any aftermarket modifications on the intake, throttle body, exhaust, or engine management system? If you've ruled out vacuum leaks, check fuel pressure—especially under idle conditions. A drop in pressure could indicate a failing fuel pump or clogged filter. Note: This applies even if the truck runs well otherwise.

Anonymous 2017-07-29 08:54

I currently use a SuperTuner scanner that allows me to read and clear codes, adjust tire size settings, shift points, and monitor basic engine parameters. I've installed a CA-legal cold air intake, throttle body spacer, and modified exhaust system—though all drivetrain components (including injectors and EGR) remain stock. I also replaced both upstream oxygen sensors as part of my earlier troubleshooting.

Anonymous 2017-07-29 09:37

Are you located in California? A cold air intake may not be legally compliant there—especially if it's installed on a vehicle with an emissions system. While such modifications are sometimes allowed, they can trigger or exacerbate lean codes. If your truck is stock otherwise, having a scanner would be highly beneficial. Without one, check fuel pressure carefully: use the old-school carburetor or brake cleaner spray test to detect vacuum leaks—quick, inexpensive, and effective. Also, verify if any exhaust modifications (like larger pipes) have been made. These can affect airflow and cause lean conditions. To test fuel pressure: observe readings at engine idle with the key off, then monitor for drops over a 5-minute period (e.g., X psi drop in 5 minutes).

Anonymous 2017-08-01 08:40

Hi—have you checked your fuel pump pressure? A low or inconsistent fuel pressure reading under idle conditions could explain the lean codes, even if the truck runs smoothly otherwise. This is a common cause of P0171/P0174 in older HEMI engines with aftermarket intakes or lift setups.