2002 Mustang GT P0171 and P0174 Codes: Causes and Solutions
I own a 2002 Mustang GT with 61,000 miles and have been consistently receiving P0171 and P0174 diagnostic trouble codes. I've already replaced both the before- and after-oxygen sensors on the right side, but the codes persist. What could be causing this issue? Are there any other potential sources or troubleshooting steps I should consider?
If you have a K&N air filter installed, it might be contaminating your MAF sensor. Even without a K&N filter, the hot wire in the MAF sensor can become dirty and trigger lean codes like P0171 and P0174. Also check the PCV valve—its hose often weakens or collapses, leading to vacuum leaks that cause these codes. Verify fuel pressure; a restricted fuel flow can also set lean conditions. Additionally, spray carburetor cleaner around both upper and lower intake gaskets, as Ford vehicles are prone to vacuum leaks in this area. Let me know how it goes—Mike