2002 F150
4.2V6
65,000 miles

I have been getting the same two codes for the past few months almost as soon as winter started (1131 and 1151) I have:

Checked for vacuum leaks

Replaced air filter

checked oil level

Replaced both upstream O2 sensors

Every time I clear the codes they return within a couple of driving cycles.

Can anyone tell me what the most common cause is for these two codes to appear. As of yet I have not noticed any proplems with performance, just the nagging codes.

Thanks,

Geoff

Any information would be a big help.

 

usually its a vacuum leak. have you checked the intake seals? when they leak, they usually leak when the engine is cold and they expand when it warms up and seal it. are you getting enough fuel pressure? any exhaust leak?

 

What is the best way to check the intake seals for a leak?

What is the best way to check for an exhaust leak?

How do I check my fuel pressure?

 

to check the intake seals just spray carb cleaner around the intake.

exhaust leak- generally you should be able to hear it but use something to clog the exhaust. like have someone hold rags at the end of the tailpipe as you listen for a leak. sometimes an exhaust leak can give an o2 sensor a false reading.

to check the fuel pressure you need to hook a fuel pressure tester to the shrader valve on the fuel rail.