Having trouble to diagnose DTC P1484 Not the EV Fan, PCM???

[vcarlos40]

Dear all,

This is my first Post, and I'm looking for some help advise.

I have a 2002 Trailblazer LTZ 4x4 I6, and love the car.
Recently I got the SES light come on and got DTC P1484, and replaced the EV Fan (it had locked) with a 25790869 one. A month after the replacemente we drove the SUV for 200 continous miles, and when heading back home the SES and REP lights came on at the same time when passing a slower moving car and accelerating. I had it scanned and the stored code was P1484. I took it to the dealer and they told me the issue was the thermostat, since they found "low cooling system performance coolant temperature low", so I had the termostat and the temp sensor replaced at the same time (the old t-stat was completely open), with ACDelco parts deleted the code and I was set, or so I thought, after driving a few blocks the SES and REP lights came back, so, back to the dealer, P1484 again, initally they asked, when you replaced the fan, was the PCM flashed? the answer is no, it was once way back in '03, when it got it's firs EV-Fan replacement, but not with this newer one. They, or so they say, swapped the Fan relay with the headlamp one to check and nothing, and also checked the damaged EV Fan harnes TSB, and mention neither is the problem. They tried to flash the PCM and mention the PCM would not take the flash, and they could not get the TB's serial number from it, so they're assuming the PCM is damaged, and mention they are surprised that the vehicle actually runs, since the PCM is damaged. I assumed the PCM entered into "safe mode", but if this were the case the TB would not shift further than third gear and it does, everything appears to run fine, reason for me to be reluctant to buy a PCM and it not be the actual issue, (obviosluy lower gas mileage), SES is on and REP comes on pretty quickly, specially when hitting the gas a bit hard.

Any thoughts?

Does anybody know the difference between the 2 part numbers out there for the PCM 12576463 and 12571178, tey both seem to be replaced by 19210066.

19210066 is 1,000 US dollars to buy in Mexico + labor to install and flash, so my thoughts were to get one from Ebay or a Junkjard, one of the other two I've found for this year model, but, not sure if it the diferent part number actually has a difference, and reflash to my car, if this were possible and the actual issue.

Your thoughts will be highly appreciated, apologize for the long post, but, needed to mention most of the story behind this.

Thanks,

Carlos

 

[vcarlos40]

I've been asking around a lot and have gotten a few second opinios, none of them believe the PCM is damaged. I'll try getting it flashed elsewhere, different dealer or a shop that knows how to do it (haven't found any yet).

I'll later post how that goes.

If anyone has further Ideas they'll be most appreciated.

Thanks,

Carlos

 

[Mooseman]

If the PCM was damaged, it would throw more than just a fan code. You can get a PCM from a junker of the same year and get it flashed if you want. Heck, you could install it yourself and just do a security relearn. It should work but you will need a CASE relearn either way.

Just for the heck of it, check the aux power fuse, which powers both the lighter and the diagnostic port. If it's blown, that would explain why the flash didn't work. If that's the case, they're idiots for missing that.

 

[vcarlos40]

Thanks Mooseman,

I checked the Aux 1 and Aux 2 fuses, and they're both good.

I was lucky enough to find a guy that has many years experience programming GM PCMs, I sat nex to help while he checked.

He plugged in a MDI to the diagnostic port which powered the unit up, he read the info on the PCM and found 3 or 4 programs in it that needed to be updated (including one for the fan clutch, he found on a GM service manual that older TBs that did not have the update needed it to be installed if they have a DTC P1484 registered and have the newer EV fan installed, so he gave it a try, as soon as he dowloaded the update from GM and tried to upload it to the PCM we heard a couple of beeps as soon as he heard them, he said, "the update is gong to fail, there's gotta be something wrong with the module" and a couple of seconds later it failed . He then said, he believed the PCM was somehow damaged and tried to reprogram an other module, and this didn't work either, so I asked him, does that mean there's something wrong with the diagnotic port or a harness? and he said that would be very rare, that it's more likely the PCM, since the update to the BCM (module he tried next) goes through it.

He'll be back today to remove the PCM and check a couple more things, but it actually looks like it is the PCM.

I'll let you know how that goes.

Thanks

Carlos

 

[Mooseman]

If he has the connectors, he could try to flash it directly instead of in the vehicle. If not, then another PCM is worth a shot. Again, a good used one will work.

 

[vcarlos40]

Thank You Mooseman,

For the 2002 model I've found two differente part numbers 12576463 and 12571178 do you or anyone know if they are compatible / equivalent (considering a used one) they both are replaced by the 19210066 (too expensive), I'm afraid of taking mine out to check wich part number is on it (it is on the non-visible area, pointing down and I can't get a mirror under there to see) and risk damaging the harness or something if I do it wrong, I see a total of 7 screws and nuts, looks like it's pretty simple, or is this risk is relatively low and I should give it a shot??

Best,

Carlos

 

[Mooseman]

Maybe your best bet is to get another PCM already pre-programmed with your VIN. I hgave dealt with this eBay seller before, no problems. Maybe just ask first to be sure it's the latest calibration version that's included. All you have to do is give him your VIN and it's ready to go.
[EBAY]310647469288[/EBAY]

 

[vcarlos40]

Thank You Very Much Mooseman, I'll get my hands on one and post how that goes.
Carlos V.

 

[BRomanJr]

I've been asking around a lot and have gotten a few second opinios, none of them believe the PCM is damaged. I'll try getting it flashed elsewhere, different dealer or a shop that knows how to do it (haven't found any yet).

I'll later post how that goes.

If anyone has further Ideas they'll be most appreciated.

Thanks,

Carlos

I do remember some folks having issues programming Modules when the OnStar (if equipped) was connected to the communications bus. I thought GM instructed Techs to disconnect it when programming any module. Apparently the OnStar module uses the communication bus often and in a way that steps on programming.

Just another situation to look into.

 

[neelskit]

I do remember some folks having issues programming Modules when the OnStar (if equipped) was connected to the communications bus. I thought GM instructed Techs to disconnect it when programming any module. Apparently the OnStar module uses the communication bus often and in a way that steps on programming.

Just another situation to look into.

I had this very same issue when I had my PCM updated a few weeks ago. I turned out the data interface for my aftermarket remote start was interfering. After I disconnected all the wiring from the interface and the remote start, the programming completed successfully. I also remember GM stating in the instructions for the update to pull the fuses for both the ABS and Lift Gate Modules BEFORE programming.

 

[vcarlos40]

Thanks Guys,

Apparently the guy did consider this, not OnStar equipped, no aftermarket stuff, and did pull the fuses.

According to him it is the PCM, I've ordered it out of EBay, should recieve it in a week or so. I'll let everybody know how that goes.

Thanks again for all the help.

Carlos

 

[vcarlos40]

Dear all,

We installed the new PCM last night, and had no luck.
The old PCM can be read, but not written, and the New PCM could not be read, since it can't be read the process won't continue.
I'm thinking the problem could be the diagnostic port (one of it's pins or sometihng like that), or a harness related to it.
Sounds like something similar to what BRomanJr and neelskit mention they had, something interfering, but can't think of where to start to look, no OnStar, no aftermarket accesories.
Could it be a ground of some kind?
I'll check all the fuses again just for the heck of it.

Any ideas will be much appreciated.

Carlos

 

[The_Roadie]

Any of a dozen intelligent modules could be interfering on the data bus. That's why there are two "splice packs" where the unnecessary modules can have their data communication lines disconnected. Helps for troubleshooting, since normally the data bus is shared among all modules. Search for discussions about these Splice Packs. One is behind the dash near the driver's left knee - the other under the rear seat hidden by a carpet flap.

 

[vcarlos40]

Thank you Roadie,

Are you refering to TSB 040845010 Splice pack 201 ground?

Carlos

 

[CaptainXL]

Assuming this is the infamous 5 volt reference circuit problem between the fan and throttle which causes the REP. I would replace the fan and harness leading up to it.

 

[The_Roadie]

G201 is involved in a lot of dash area problems that could include module communication. But the data comm splice packs I mentioned are called SP205 (pictured in this thread: http://gmtnation.com/f23/whats-harness-3017/)

View attachment 6177

and SP306 under a carpet flap under the rear seat.

View attachment 28119

 

[vcarlos40]

Thank you so much, sorry for the possible dumb question, I'm not good at all with electric stuff, should I check for frailed wires or disconnect and connect one by one to isolate the module that may be interfering?
Carlos

 

[The_Roadie]

The splice packs are to allow easy disconnection of one module at a time to see if interference goes away. It could be bad modules or bad wiring. Not a good troubleshooting project to learn electronic principles on the job. Recommend you find an experienced friend or pay somebody.

 

[vcarlos40]

Roadie, thanks again for the reccomendation,

I found this on the net:

EASE Online Support Web Site

Anyone ever heard of this?

It kinda checks out with what you're mentioning regarding SP205...

I'll definitely not mess with it on my own, I'll have someone that knows how to handle this.

Thanks Again,

Carlos

 

[meerschm]

G201 is involved in a lot of dash area problems that could include module communication. But the data comm splice packs I mentioned are called SP205 (pictured in this thread: http://gmtnation.com/f23/whats-harness-3017/)

View attachment 6177

and SP306 under a carpet flap under the rear seat.

View attachment 14500

I love it when I learn something new.

Thanks

 

[vcarlos40]

Dear all,

Just an update.

I found SP205 without any problems, It has a comb shaped plate to jumper all the modules together.

We removed the comb and jumpered A and B (comunications bus and PCM) and went for it!.

The read of the PCM was much faster than before, (we got 2 DTCs this time, P1484, and I don't remember the other one, but it was related to communication loss, due to the disconnect of the other modules) deleted the codes and gave it a try, unfortunately it would not update, we replaced it with the new PCM I got from Ebay, and we couldn't read it, we removed the jump and re-installed the comb and had the same results.

Only this time we were able to update the BCM and the PDM.

At this time, there are two theories we are looking into:

1) New PCM is faulty.
2) New OEM PCM is completely blank (no OS on it), Scanner won't read it (nothing to read), so update won't go through.

For #2 we're looking to get the OS from GM to download to it.

Any other idea, will be much appreciated.

I already mentioned this to the Ebay seller and is willing to send a replacement if this doesn't work.

Best Regards

Carlos V.

 

[vcarlos40]

Dear all,

Just wanted to thank everyone for all the help I received and share the solution:

We sent the PCM back and got a refund, I then purchased a second one programmed to my VIN as Mooseman suggested, put it in there myself, did a security relearn (instructions came with the PCM) and fired it up (strange, but no CASE relearn was needed), drove it around the block and P1484 Again!!! , so I went and ordered a new Fan clutch, and while taking it apart found that the fan and fan shroud were damaged, replaced those also, deleted the code, and Bingo!:wootwoot:

It's been running smooth for a week, improved gas mileage. My mechanic believes, that since the fan clutch was new the fan being out of balance could of damaged the Fan clutch, still no clue of why the PCM would not take updates, so, it still was a good idea to replace it.

Quite an ordeal, but finally solved.

Carlos V.

 

[Mooseman]

Glad you finally got it. I absolutely hate the EV clutch so much that I went to Efans.

 

[vcarlos40]

Dear all,

Sad to say, I got p1484 again. I'm reluctant to think it's the Fan Clutch, since as you know i very recently installed a new one, for the second time.

The post:


CaptainXL

Posted 13 May 2013 - 06:18 AM
Assuming this is the infamous 5 volt reference circuit problem between the fan and throttle which causes the REP. I would replace the fan and harness leading up to it.



Is telling me I should have also replaced the harness, could you please point me in the right direction of the part number I should look for? Or as always, your ideas are more than welcome, and worth a shot.

As always, your priceless help will be much appreciated.

Carlos