03 Tahoe Flasher causing PCM problem???

dbcomm · Post by **dbcomm** » Sat Jul 10, 2004 6:41 pm

Pardon the length of this post -- Just trying to get all the info in.

Recently, I installed a Galls FS005 headlight flasher in a 2003 Tahoe. According to Galls, a modification must be done at the power center under the hood. It calls for the installation of a diode on your choice of 2 white wires coming from the block. Well, this tahoe didn't have the two wires in the location noted - it didn't even have 2 white wires under there period. So, what I did was located the two wires that operate the high beams, on for left and on for right (I was surprised that there was a seperate wire for each side at the power center). I verified that the wires to each headlight were punched down to the same connector at the power center, and then cut both wires. I posted an image that explains this a little better at http://dbcommunication.com/untitled1.bmp

A few days after this install, the Tahoe displayed "Service 4WD", the voltage level varies dramatically (9-14V) while driving, and the ABS light and chime will happen occasionally.

Any ideas or thoughts would be appreciated. Thanks.[/img]

c17loadsmasher · Post by **c17loadsmasher** » Sat Jul 10, 2004 6:53 pm

Isolate the flasher as the problem. Clear the faults in the truck, reconnect the wires as they were before the flasher was installed and see if the fault codes trip, and the behavior continues. Then you know for sure whether it's the flasher or not. Maybe something else got disturbed during the work on the power center.

dbcomm · Post by **dbcomm** » Sun Jul 11, 2004 7:39 am

I forgot to mention, I took it to the dealer, and it never threw any codes. I just hope this is a big coincidence.

KitN1MCC · Post by **KitN1MCC** » Sun Jul 11, 2004 7:53 am

that is one reason why it is not recomended that u install any find of flasher on the newer chevy.

2 options get the whelen soft plug in halogen 50 watt bulbs

or install clear strobes

commtek · Post by **commtek** » Sun Jul 11, 2004 8:16 am

I remember jim posting the answer to this problem on another forum. There are two versions of DRL on these vehicles, and the solution revolves around which one you have.

As was stated before, remove the flasher and start from point zero.

Friends don't let friends use Galls products.... Contact Sound Off at http://www.soundoffinc.com who builds REAL flashers.

dbcomm · Post by **dbcomm** » Sun Jul 11, 2004 12:11 pm

maybe I just don't understand what the deal is with the DRL's. They are an entirely different assembly all together. What do the DRL's have to do with installing a flasher on the high beam circuit?

c17loadsmasher · Post by **c17loadsmasher** » Sun Jul 11, 2004 2:37 pm

commtek wrote:Friends don't let friends use Galls products.....

I thought that went without saying.

The flasher I have in my 2002 TrailBlazer is a Whelen UHF2150A...no problems. I just replaced a Galls headlight flasher in our squad truck that went Tango Uniform a few weeks ago with another UHF2150A and it works juuuusstt fine.

bnn121 · Post by **bnn121** » Sun Jul 11, 2004 2:43 pm

I had the same problem on two 2003 Tahoe's.

Its been a while..but if I'm not mistaken. There are two versions of this flasher. One that is positive ground switched and the other a negitive ground switched headlight system.

I cant remeber which model was which.

Something to look into.

But I did end up having the wrong version to start with and got the correct one and it works like a champ. I'll see if I can get the model humber of the one that works and post back here.

commtek · Post by **commtek** » Sun Jul 11, 2004 4:49 pm

dbcomm wrote:maybe I just don't understand what the deal is with the DRL's. They are an entirely different assembly all together. What do the DRL's have to do with installing a flasher on the high beam circuit?

2003 was a bastard year and the high beam switching could be determined by which DRL scheme they used. I don't remember the specifics, would have to look at one again.

FMROB · Post by **FMROB** » Sun Jul 11, 2004 7:07 pm

Do yourself a favor....

1) Determine (without a doubt) how your hi beams are switched.

2) Buy yourself the appropriate WHELEN head light flasher.
Either a UHFPOS or UHFGND

In this particualr model GM truck the DRL are in a separate light fixutre and circuit, and do not have anything to do with the hi beams. The flasher should be isolated from the DRL circuit if installed as per the directions. All it is is just two wires to the one driver side HL.

good luck

dbcomm · Post by **dbcomm** » Sun Jul 11, 2004 8:08 pm

The fs005 flasher installed is positive switching. The highbeam headlights on both sides have a constant ground and BOTH have an isolated wire that terminates in the power center. By applying 12VDC, using a standard test probe, to the relay in the power center, the relay closes and provides 12VDC to each of the high beam lamps (driver and passenger). As stated earlier, both wires connect to the same block in the power center. The FS005 flasher I used is "DRL compatible" so it has a relay that is NC while off and open when the flasher is activated. As shown in the diagram in the first post (which was crude-sorry, I had just gotten up) I used the NC relay circuit to TOTALLY isolate the flasher from the vehicle when the flasher is off. To the Tahoe, it should appear that everything is factory. Anyway, I'm baffled.

I did isolate the flasher just to check, but same thing. Again, hoping it's a coincidence.

dbcomm · Post by **dbcomm** » Mon Jul 19, 2004 6:51 pm

Well, when having a Chevy serviced for a toally unrelated repair (intermediate steering shaft.....major problem for later model chevy/GMC's) always make sure that the service tech with a 4th grade education RE-ATTACHES THE GROUNDING WIRE FROM THE ENGINE BLOCK TO THE CHASSIS!!! After four trips to the dealer, somebody noticed it. I'm not totally sure why it was removed in the first place.

apco25 · Post by **apco25** » Mon Jul 19, 2004 8:59 pm

Commtek, any chance you looked up which switch which in 03?

dbcomm · Post by **dbcomm** » Tue Jul 20, 2004 10:31 am

Apco-

I reinstalled the +switching flasher after determining the problem was in fact the ground strap from the block to the chassis. Even though it's a Galls flasher, it appears to be functioning correctly now. I am using the built in relay in the flasher to isolate it from the electrical system while operating.