dreaded P1389 code-Fried PCM
So it finally happened....I kept saying....not me...wont happen to me....dang!
Gotta find a new PCM....but what caused the evil burn.
What I know: (or think I know)
ASD (auto shut down) circuit which controls the injectors, coil, alternator all on the same circuit. Sometimes, when the ASD system malfunctions, it shuts down and the truck will crank but not start. (sometimes it is the coil itself, sometimes the alternator, sometimes a fuse for the injectors) I was not so lucky, the relay is fine...swapped it out with others of the same rating....a spike (caused by SOMETHING PROBABLY GROUNDED) went straight to the PCM after the relay.
Guess what....the voltage regulator is housed INSIDE the PCM.... so if a spike occurs after the relay it fries the PCM????? (alternator internal ground???)
Pin 12 on PCM block (ASD) circuit is a common problem. when I opened up the wiring loom there, it smelled of burnt circuit board and around that pin was all melty and oozy....
I think it may be the alternator....
start up after a long siesta is always interesting....all kinds of noises, squeaks, tappets, belts, smoke from 2 tons of wd40, ect......and it did its share of squawking.
I guess I ll get the alternator tested...but this kinda sucks. (gauge for alternator read in the right ranges and did not show any spikes while I was getting it going again) Some guys have put a 3a fuse at that wire on the PCM and it has helped in most situations. They do this while figuring out what actually causes the spike. Some guys have fried 3 pcms not knowing the cause of the spikes and just trusting the fact that the PCM was the cause and had an internal issue. (This is true over time, they do have issues. not enough solder on some of the hardware inside the PCM is usually the cause. Heat and vibration are another cause.)
I can buy a whole parts truck for what they want in parts!
Can anyone shed more light on what to do BEFORE hooking up a new PCM....they are 150-200 bucks (unless you take your chances on ebay)
Last edited by DakotaJP; 05-22-2017 at 09:14 PM.
Reason: correcting assumptions made before I learned more!