1998 Ford F150 - 4.6L PCM Won't Reset FIXED

[joetngallagher]

I appreciate all the assistance y'all have given me. I checked everything you have suggested. Every sensor and system is running fine. BUT!!!!! NO MONITORS will reset. Every monitor continues to say NOT READY. Can the PCM have a problem of not doing ALL the tests?

[steven kiser]

are there any codes? if the pcm is the culprit the check engine light should be on. if it was used and thrown into the truck it may be the issue. check the #'s. check to see if an 02 is melted to the exhaust pipe. i've seen manifold leaks melt harnesses near the fire wall. i believe the only programed way it can do this is if it goes into limp or default. that is a progran=mmed fall back program that allows the vehicle to function at a base setting. is there a performance issus to go along with this? i'm assuming the check engine light is functioning. if you can read the 02 through the scanner and they're not flat then the 02 monitorshould set. driving at 30 mph for about 5 miles then at higher speeds for another 5 miles should set the egr. what's the temp reading on your scanner. see if any of the sensor readings are way out of whack. i've seen "universal" 02's wired incorrectly causing issues. what happened right before this all happened. was it sitting for a long period of time? there may be "critter damage".

[a&mauto]

I would be looking in the direction of the "keep alive memory".

[joetngallagher]

"OK" here's the data..all 4 o2's are OE and switching properly and withing Mv specs. Eng Temp id 93C. IAT is 20c. DPFR, vacuum valve & EGR valve operating properly and intake passage is clear. There are no codes present or stored. PCM is OE. Vehicle sat on car lot for approx 3 months but has been driven 2200 miles since purchase. Customer did not know there was a problem until he went for emission test 3 weeks ago. Testing center told him someone must have cleared codes and vehicle was in drive cycle mode. Customer drove for 2 weeks and had it retested. Same scenario. Brought to our shop one week later on May 22. Scanned PCM and CATALYST, EVAP SYSTEM, OXYGEN SENSORS, HEATED OXYGEN SENSORS & EGR SYSTEM monitors are NOT READY. Truck runs fine.

Steve Kiser, Tim Martin, Rocmorin and many other responders....I want to personally thank you for the support and time you lend to this forum. I read the forum daily and you always have great advice. I'm 62 years old and I am learning something new every day.

[brianp87]

Gotta be the pcm if it is not the keep alive power. Pin 55 if is good then pcm no question

[ricmorin]

Check cranking voltage. Is it possible that, during crank, the voltage is dropping just below the keep-alive threshold? Worth a look.

[steven kiser]

if it sat for a while and let's say for the sake of argument joe joe the dog faced boy went to start it. it cranked slow, he put the jumper pack to it and low and behold he left the key on. if all the fuses are good he probably did blow the pcm. it seems the pcm is reading but i wonder if it's making adjustments, i'de check the timing changes while it's running, if there are no changes it just solidified the pcm being trashed. take a quik look at the battery cabe ends at the battery. f they look like there was a flash melt the cables could have been put on reversed. replace pcm.

[steven kiser]

oh ya, one more quickie. tell customer he may have a pandoras box here.............................................

[Tim Martin]

At the risk of someone saying that he thinks he is good, I wish I had that truck at my shop. Not that I could garantee I could figure it out but the challenge would be worth a good run. Do you have a good relation with the local Ford dealer that you could get them to look at it? I have already done that and it has helped. Ya got a good one, I''d say. Keep us posted.

[Tim Martin]

Oh yea, I forgot to respond to the post thanking a few of us for our contribution to this forum. Tell ya what, I have been helped so much by others when I went into business for my own that I feel a deep sense of obligation to return the favor to others. But I think it is great when we can help each other in the work we do. No one of us regardless how long we are in business knows or ever will know it all. I'm only 51 years old and feel like I've got much to learn about the technology of todays vehicles but we are trying.

[joetngallagher]

Patience prevails.........While checking a wiring diagram on the keep alive memory I saw that one of the diodes in the engine PDC was linked into the system. One of the diodes in the engine PDC had corroded spades(no cover on PDC and diodes are closest to fender/hood opening). Took a shot at cleaning and reinstalling. Monitors are resetting. KOEO and I didn't hear anything when I removed them but after cleaning and reinstalling I heard a relay click. Gonna make customer happy he only needs a fuse box cover instead of a PCM, but labor charge will darken his mood. Praise the LORD

[steven kiser]

congrats......................h ya, thanks for posting the fix.

[Tim Martin]

Thanks for posting what the fix was. Today's vehicles and their issues are often electrical in nature and your vehicle there sort of illustrates the point I want to make. Getting acquainted with the wiring diagrams has often led me to a fix on a challenging situation. And in your case it also certainly has. The other point I want to make is that I often as a vehicle is FIXED! I breather a sigh of relief and just say "Thank You God 4 The Help" I firmly believe that God plays an important role in my auto repair business and I want to give Him credit for it. Also, the amazing techs that come on this forum are a source of tremendous help as well. Many thanks to you all and my hat is off to ya!

[brianp87]

Any body know what the kap voltage is supposed to be? both me and joe are unable to find it

[Tim Martin]

Isn't KAP usually battery voltage?

[brianp87]

So it shoud be the same voltage as at the battery. If so joe may still have an issue

[Tim Martin]

I just looked it up and according to the wiring diagram Mitchell provides me with, KAP comes directly from Fuse 1 (5amp fuse) in the Engine Fuse Module on the left side of engine compartment.

[ricmorin]

Battery voltage for keep-alive.