New Mega Fuse Changes Driver

jabshire

Original poster
Member
Mar 4, 2013
4
Hello all,

Does anyone know why changing the megafuse from a fuse block from a junkyard would cause the Driver to change from Driver 2 to Driver 1?
Is it JUST a fuse or is there data storage in there? Doesn't make any sense to this noob.

Also, can anyone tell me whether the fuse block from a 2004 GMC Envoy V8, VIN 1GKES16P946133647 will work in a 2003 Chevy Trailblazer V8?
I swapped them because of the headlight relay meltdown, all accessories seem to work, but when the key is turned to the ON, the gear selector underscore disappears, and the engine won't start.
I suspect it's some kind of anti-theft programming in action, which I was hoping to get around, or the fuse blocks aren't compatible. NOT interested in shelling out over $600 for a new one. Ugh.

Thanks in advance for any insights.
 

AbsoluteZero

Member
Nov 21, 2011
211
jabshire said:
Hello all,

Does anyone know why changing the megafuse from a fuse block from a junkyard would cause the Driver to change from Driver 2 to Driver 1?
Is it JUST a fuse or is there data storage in there? Doesn't make any sense to this noob..

When my 03 "forgets" who's driving I've been successful in reprogramming it's mind by locking and unlocking with the correct remote. Do before putting the key in the ignition.
Can't help with your other issue.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The Megafuse is only a fuse. The vehicle can actually start and run with it missing, since it only runs convenience items like interior lighting and HVAC functions.

I'm not sure about the fuse block. Were all the fuses and breakers inthe same locations in both blocks? A part number investigation at http://parts.nalleygmc.com/ might be in order.

What is the state of your security light?

Smells like an ignition switch fault to me. Have you ever changed it?

When you sat "won't start", do you mean "won't run the starter" or "turns over but won't run"? Vastly different troubleshooting paths for those two symptoms.
 

jabshire

Original poster
Member
Mar 4, 2013
4
Hi folks, thanks for the replies.

RE: the megafuse, what would cause the key to be recognized differently simply by swapping out the megafuse from one fuse block to the other?
With the 'new' fuse block installed, I can swap the original megafuse with the 'new' one and get the correct driver 2 recognition behavior. That's why I was thinking there may be some data stored in that part. That, and they label that as the "Instrument Panel Battery" on the fuse block schematic.

RE: the fuseblocks, the part numbers are not the same, 15196421 for my 03 Chevy, 15196418 for an 04 Chevy or GMC.
Fuses and relays matched up, with the exception of optional gear on the 04 GMC for the Electric Adjustable Pedal.
Tried pulling fuses and relays for the optional equipment not on my vehicle, but engine still wouldn't crank.

With the 'new' fuse block installed, turn key to ACC, key is recognized as driver 1 (should be driver 2).
Gear selector underscore lights under P, vehicle in Park.

Turn key to ON, gear selector underscore light goes out. Also note that at this stage I cannot move the gear shift lever.
(Will re-verify that the Automatic Shift Lock Control System fuse is good in the 'new' fuse block)

Turn key to START, dash lights go off, but doesn't crank.

Reinstall old fuse block, turn key to ON, gear selector underscore light stays ON, turn key to START, truck starts no problem. (Except for the low beams of course, because that slot for the HDM relay is melted, relay removed, which is what started me down this road...)
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The fob memory stuff is all located in a "seat memory module" under the driver's seat, which handles the seat and mirror memory settings and communicates to the BCM, which is the master controller that sends data messages to the radio to change the presets for the two fobs.

I haven't thought of any possible way the fuse block could cause fob confusion.

But your experience shows there is some fatal difference between the two fuse blocks. It would require access to the shop manuals for both years (I have only the 2004) and a few hours research, to discover the root cause here. I would PM you my rate for private consulting, but it would ultimately cost you more than buying the correct fuse block from another source. I predict - I may be wrong.
 
Dec 5, 2011
577
Central Pennsylvania
jabshire said:
Hi folks, thanks for the replies.

RE: the megafuse, what would cause the key to be recognized differently simply by swapping out the megafuse from one fuse block to the other?
With the 'new' fuse block installed, I can swap the original megafuse with the 'new' one and get the correct driver 2 recognition behavior. That's why I was thinking there may be some data stored in that part. That, and they label that as the "Instrument Panel Battery" on the fuse block schematic.

RE: the fuseblocks, the part numbers are not the same, 15196421 for my 03 Chevy, 15196418 for an 04 Chevy or GMC.
Fuses and relays matched up, with the exception of optional gear on the 04 GMC for the Electric Adjustable Pedal.
Tried pulling fuses and relays for the optional equipment not on my vehicle, but engine still wouldn't crank.

With the 'new' fuse block installed, turn key to ACC, key is recognized as driver 1 (should be driver 2).
Gear selector underscore lights under P, vehicle in Park.

Turn key to ON, gear selector underscore light goes out. Also note that at this stage I cannot move the gear shift lever.
(Will re-verify that the Automatic Shift Lock Control System fuse is good in the 'new' fuse block)

Turn key to START, dash lights go off, but doesn't crank.

Reinstall old fuse block, turn key to ON, gear selector underscore light stays ON, turn key to START, truck starts no problem. (Except for the low beams of course, because that slot for the HDM relay is melted, relay removed, which is what started me down this road...)


Check fuses. I'll bet dimes to doughnuts that you've got a bad (loose) fuse slot and that you've got at least one fuse "wiggling" around.
See my thread / post: http://gmtnation.com/f23/intermittent-starting-problem-all-but-gas-gauge-works-no-fuel-pump-no-crank-5999/index2.html#post120466.

While my symptoms were a little different - it seems as though yours has similar issues (no crank, dash lights go out, gear indicator out). When you turn the key, your HVAC shut off? Everything acts like it's going to start, but doesn't, right? Fuel pump running?

Check fuses #10 and #28 (PCM1 and PCMb, I think). Make sure they are not loose! If you find that one is loose, wiggle it gently back and forth slowly with the key in the on position. If you get a relay-like clicking sound you've found your loose fuse. Pull the fuse and twist the legs ever so slightly. Reinstall. Retry start.

If it's not the fuse(s), it sounds like you're not getting power to the PCM. When installing the replacement block, are you tightening the through-bolts enough? (don't overtighten)
 

Forum Statistics

Threads
23,397
Posts
638,827
Members
18,611
Latest member
DirtEater73

Members Online

No members online now.