my 98 f150 4.6 has 160000 miles on it. I changed the spark plugs when it started to miss under a load and the ckeck engine light came on. the spark plugs took care of the missing and the check engine light. drove it 150 miles and the light came back on. does the code need to be erased.

 

Yes the code needs to be cleared. The easiest way to clear the check engine light is disconnect the negative battery cable for a few minutes.

 

The CEL is probably on because there are additional or recurring faults. Most common are codes for EGR system faults, O2 sensors/vacuum leaks, and other such stuff.

Get the codes read before reseting them, that way you'll have an important clue as to WHY the CEL is on.

Steve

 

My cel problem is taken care of took my truck to auto parts store and ran test came up with a 401 code. Found out it meant irregular exhaust reading. I checked for vaccum at the egr and found very little so I traced the lines and found a group of lines between the battery and firewall that had come apart. So far so good and thanks for the help.

 

There isn't supposed to be vacuum at the EGR valve in your driveway. The computer only opens the EGR valve (applies vacuum to it) at certain engine and ground speeds. Also, it takes two consecutive drive cycles with EGR monitor self-test failures to set the CEL to on. Perhaps you haven't fulfilled that yet.

OTOH, that vacuum line you found is likely the one that runs to the climate control system so it should be working correctly now. It might also have been the supply to the EVR solenoid (which switches the vacuum to the EGR valve) so you may have hit it on the nose.

P0401 codes are extremely common. Usual suspects are the EGR ports are clogged or the DPFE sensor is faulty. Do a vacuum test to diagnose.

Steve