OBDll codes P0171, P0300 & P0131 for 2017 Chrysler 300c

Question

I have a 2017 Chrysler 300c with check engine light on. Reading codes P0171, P0300 & P0131. About a month ago it was code P0128. The coolant thermostat that was installed wasn’t the right temperature so we replaced it with a higher temp thermostat. Engine light went off for a few weeks but now it’s back on and reading those 3 codes. Spark plugs are bad so I know those need to be replaced and possibly the O2 sensor but this was done about a year ago. The spark plugs installed at the repair shop were not OEM parts which I believe is why they went bad but is there something else going on? I feel like there’s more to it then just spark plugs and 02 sensor. Is there something causing these to go bad or is it just all related? I don’t know much about how all this works so any advice would be much appreciated.

Answer 1

You're dealing with a combination of codes that could be interconnected, especially since you've recently replaced a thermostat and you’re seeing codes related to air-fuel mixture and misfires. P0171 - System Too Lean (Bank 1), P0300 - Random/Multiple Cylinder Misfire Detected, P0131 - O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1) and P0128 - Coolant Temperature Below Thermostat Regulating Temperature.

Spark Plugs: Non-OEM spark plugs can absolutely cause issues, especially in a sensitive engine like the Chrysler 300C’s. If they weren’t designed to the manufacturer’s specifications, they might not be firing correctly, contributing to both misfire (P0300) and potentially a lean condition (P0171).

Vacuum Leaks: Since a lean condition is being reported (P0171), it’s critical to inspect for any vacuum leaks, such as cracked hoses, intake manifold gaskets, or throttle body seals. These could be letting excess air into the engine.

O2 Sensor or Fuel Issues: While the O2 sensor was replaced, the P0131 code suggests it might not be functioning properly, or there could be another issue affecting its performance. Since this sensor helps monitor and adjust the air-fuel ratio, its malfunction can worsen the lean condition. Additionally, low fuel pressure or clogged fuel injectors can also contribute to a lean condition and misfires.

Start by addressing the known issues (spark plugs), but also follow through on vacuum leaks, O2 sensor diagnostics, and fuel system checks to avoid the same problems cropping up again. The issues are likely related to air-fuel mixture control, which can impact multiple parts like the spark plugs and O2 sensor, so fixing one might alleviate the others.

1. Replace Spark Plugs with OEM Parts: Since you already know the spark plugs are bad and non-OEM, I would start by replacing them with OEM plugs.
2. Inspect for Vacuum Leaks: Given the P0171 code, a thorough check for any vacuum leaks is crucial. Look at intake hoses, the intake manifold gasket, and throttle body seals for any cracks or leaks.
3. Test the O2 Sensor (Bank 1, Sensor 1): Even though the O2 sensor was replaced a year ago, it’s possible that it's faulty again or that wiring/connectors are damaged. Testing it with a multimeter for proper voltage or replacing it may be necessary.
4. Check Fuel System: Verify that the fuel injectors are functioning properly and that fuel pressure is within spec. A weak fuel pump or clogged fuel injectors can cause both the lean condition and misfires.
5. Inspect Exhaust System: An exhaust leak before the O2 sensor can cause incorrect readings and affect the air-fuel mixture. A close inspection of the exhaust manifold and related components is recommended.

Comments

Thanks for taking the time to respond to my queetion and helping me to understand it all a bit better. Definitely plan on following your advice!