For six years, my car, a 1999 model with a 4.6L engine, has been showing a P1131 code off and on. This code means the oxygen sensor in the front of the engine is detecting too little fuel. Sometimes the code stays for a few weeks, then disappears for a while. It often happens after I fill up the gas tank. I’ve already changed the gas cap and made sure it’s tight.
Despite this code, my car runs smoothly without any problems. It starts fine, idles smoothly, and I get around 17-18 miles per gallon.
The “Check Engine” light turns on about five minutes after I start the car, and P1131 is the only code it shows. If I clear the code, it doesn’t come back while the car is running. But if I turn off the engine, let it cool down, and start it again, the code returns. I’m not sure if this pattern is important or not, as I don’t fully understand how the code system works.
There’s a technical service bulletin (TSB) about possible leaks in the bolts or gaskets between the upper and lower intake manifold, which can cause similar issues. However, I’m hesitant to take apart the manifold when the engine is running fine.
Do you have any ideas about what else might be causing this?
Ok, @Arthur, The P1131 code in your car could be due to a few things. A faulty oxygen sensor is less likely since your car runs smoothly and has good gas mileage. More likely, there’s a vacuum leak in the intake manifold, as suggested by a technical service bulletin (TSB) for your model. This leak can cause a lean condition (too little fuel), triggering the code after refueling and disappearing while driving. Other potential causes include a faulty fuel injector, a malfunctioning mass air flow (MAF) sensor, or loose wiring. To fix this, you should get a professional smoke test to find any vacuum leaks, consider a fuel system cleaning, and check the specific TSB for detailed repair steps. Addressing this issue is important to prevent long-term engine damage.
The P1131 code on your 1999 car indicates a lean state (short of gasoline) despite high performance. Possible causes:
Faulty oxygen sensor: The sensor may be sending inaccurate indications.
Vacuum leak: unmetered air enters the system through leaks.
Fuel system difficulties include blocked injectors or a faulty pump that restricts fuel flow.
The possible solution check for vacuum leaks first. If there are no leaks, consider testing the oxygen sensor. Look up the TSB for your car’s intake manifold leaks. While the car now operates properly, fixing the code is recommended for peak performance and emissions.