Fried plug at fan blower switch? What causes it? "REP"

[txab]

Always replace the plug with the resistor

[ifixedit]

BINGO! I was going to mention the radio static / ignition noise when the radio is on AM but figured it had nothing to do with it, but...... then again I was thinking, who the hell makes a late model truck and offers such a poor arrangement for the radio that the truck would suffer from the old fashion ignition buzzing on AM? You are the first one to ask if the radio is making ignition noise on AM. IT IS and has been doing it for a long time! I once disconnected the plug to the radio and gave it a good coating of dielectric grease, the static and ignition buzzing went away for a few days and then it was back and has been doing it again ever since. It does seem to kind of come and go, some days real bad, others barely noticeable, usually gets much worse either at night, near electrical lines or when I drive under a bridge or a canopy as a gas station. Before I yanked the bad fan switch, if I turned the fan on or turned the headlights on manually you can hear the static "click" on the radio (like the switches are really dirty) which keeps leading me to believe it's SOMETHING going on in the dash wiring that's causing the reduced engine power mode. Or is it? Interesting but the worse the radio buzzes / ignition static is on AM the more often it has gone into REP, so I've felt all along this has SOMETHING to do with it or is at least a warning sign that's something is wrong. Even with the fan switch out and the plug cut off, the fan off, the ignition static and the static "click" if I turn on the headlights is still there, so that has yet to go away no matter what. What is the source of this? I also thank you for confirming this COULD interfere with the drive by wire, I just can't see how it couldn't, I just have to find the source of the problem now.

 

I was under the dash again this weekend looking for any signs of loose wires, water intrusion, critters, wiggled stuff while the truck was idling, checked under the power box under the hood again with is running, wiggled wires, flipped open the panel that holds all the fuses and relays, nothing, could not get it to go into REP.

 

I relocated the TAC ground I made from the lug on the firewall to the engine where the two bolts hold the metal bracket that secures the positive cable near the alternator. I performed a voltage drop test there, I get a 0 reading with the multi reader set to millivolts with engine off, but the reading goes up a little with the truck running. I am also wondering if I have a ground that gets worse as the under hood temps go up? It has always only done it once fully warmed up. Also if this is any clue, it has NEVER done it with the cruise on and activated, only when using the throttle manually.

 

By the way, what is this BCM (what does BCM stand for?) you mention? Where is it and what does it do?

 

We're making headway!

[ifixedit]

OK, I looked it up, seems BCM stands for body control module, the thing with several plugs connected to it just under the dash on the drivers side. Will inspect that tonight and look for a possible bad connection / wires or ground there as well. Is it possible something going on with the BCM is causing all the ignition static on the radio when it is on AM?

 

Anything else concerning the BCM I should be looking at?

[w3jn]

You'll hear all kinds of noise on AM - I'm suggesting you turn on the fan and see if you have a big increase in noise.

 

The body control module does a lot of things inside the car - lights, A/C etc. The problem most certainly isn't in either the BCM nor the PCM but rather electrical noise, a bad ground, etc., that's confusing one or the other. Don't worry about the BCM for now.

 

As long as you have your millivoltmeter out, check the voltage between the battery negative and the dashboard frame when the engine is running and the fan is going. If you see any appreciable voltage the dashboard doesnt have a good ground. Also find out where the fan motor is grounded and check the voltage at that point to the battery ground.

 

If yours is anything like my 02 Suburban there are some wires under the hood that are shielded (they have aluminum sheathing on them). These wires go to sensors that are particularly sensitive to electical noise - make sure they're routed correctly and the shielding is in good shape.

[gmtech4]

how old are you ifixedit ?

[ifixedit]

how old are you ifixedit ?

HA! Waaay too old to be messing around with this junk! Yes, this 03 crew cab is gonna get an M-16 soon! I'm seriously considering going back to carburetors, and something from the hey days of the muscle cars if that gives you any idea of my age.

 

I stopped at two auto parts stores on the way home, the local Carquest guy who I normally trust searched for 20 minutes and said he'd have to call his "guy" to come up with a new fan switch and to call him tomorrow with the results, the local NAPA guys also scratched their heads for 15 minutes and finally told me they only come up with a complete head unit @ $149 (mine is the one with the two round dials and the two sliders for the heat control) but didn't have one on hand, so I could not test the fan circuit tonight. So, I decided with nothing else to do that I'd take another look under the dash and in particular that BCM. I've either made things worse or perhaps have made whatever is actually casuing the problem to REALLY rear it's ugly head in spades now as the thing went totally bizerk tonight! I first disconnected the battery and proceeded to remove all the plugs from the BCM. I even took it out and inspected it, every contact looks like brand new, no corrosion or any signs of any kind of contact issues at all, I even opened it up and looked inside to see if anything was burned or out of the norm (I didn't touch anything inside) and all looks fine. I applied dielectric grease to all the plugs and worked it in to the sockets and put it all back together. I reconnected the battery and the second I turned the key to the run position the display immediately said REP (has never done that before). I cycled the key on and off a few time but still did not start the truck. The REP went away after about the third try so I proceeded to start it, it started right up and went to idle normally. I let it warm up for a few and took it for a drive, seemed to be running fine as before. I got about 3 miles from home on the highway at about 60 and bing-bing REP, but now it ALSO does it even when I let it coast (again, never did that before). Pulled over to a stop, shut it off, waited a few, started it up and all is once again fine but the check engine light stays on as it has done every time in the past after going into REP, got it home and pulled into the garage. I shut it off, wait a few seconds and turn the key to the run position (without starting it), it goes bing-bing a few times and the REP shows up again, I repeat this a few times and then it again quits displaying REP. I start it up and take it out for another drive and pretty much get the same results, quits both holding the pedal steady and while it's coasting. I come home, turn the key to run and REP again. I turn the key to run and press down on the accelerator a few times and all of a sudden it says change oil (I just did and reset it), then all of a sudden it says oil life reset. So now it's gettin really weird and it's getting all kinds of bizzare information by seemingly totally non-related things! I cycle the key a few more times and it only bings once now and can't get it to repeat the REP with the key in the run position. I also started it and let it idle while I wiggled and pulled on the wires to the BCM and other wires under the dash for good measure and could not get it to go into REP, so go figure.

 

It got too late to stop at NAPA to borrow their scanner to see what codes may now pop up, so I'm going to stop in the morning and see if it's the same old P1516 code (TAC, I've already replace the TAC with a new one) or if something new is now showing up.

 

I recently regrounded both the PCM and the TAC, I'm now wondering if I've over-did it with the grounds and it now just does not need this if there is such a thing? Whatever I did to the BCM tonight by applying dielectric grease to the plugs has sure got it doing something new it's never done before, but it's all new in a bad way. I'm driving the old backup 98 Yukon to work tomorrow, at least the damn thing runs without giving me any grief, and it has a throttle cable to boot! In my opinion drive by wire = crap! There is another 4 letter word that begins with S and ends with a T to describe it, but I'll refrain from using it.

[gmtech4]

holy crap !!!

[ifixedit]

ok, maybe some good news this morning and my messing with the BCM was a good thing afterall. I stopped by the local NAPA this morning and scanned it, of course on the drive over it just had to do one REP on me. The only code the truck has ever thrown in the past is P1516 (TAC) which in my opinion is a bit vague as since I've replace it with a new one and it has continued to only give me this code up until today that is!

 

Along with P1516 today it spit out three codes it NEVER has in the past. Codes P0220, P1518 and P2135, all directly related in one way or another to issues with the TPS (which is built in to the TB on mine) or issues with communication between the pedal and the TB.

 

So, here's three questions:

 

1. Did my applying dielectric grease resolve some kind of intermittent or poor communication between the BCM and the PCM and now the thing can finally tell us what's actually wrong? Again, before the ONLY code has been P1516, never any others.

 

2. I just installed a re-man AC Delco throttle body in the past month, what are the odds the throttle body was bad from day one? I have visions of the AC Delco rebuilder doing a few tests, cleaning it up a little and saying "yeah this one looks fine" without ever opening it up and looking inside and sending back out the door.

 

3. Being on the surface it at least appears there's possibly been some kind of issue with the BCM communicating properly for a long time, did I incorrectly diagnose a faulty new TB in the past? I did put on one new TB in February and the truck ran without issue for 4 months, then started the REP thing again which is when I decided at the time to go with the re-man AC Delco unit. The truck ran for about a week after installing the AC Delco re-man and was right back to it's old tricks.

 

I have replaced the switch on the pedal in the past with a new one along with all the other things I mention earlier and none of it helped, so I'm assuming the pedal switch is fine. The local NAPA guys agreed to once again replace the re-man AC Delco TB with a new one and refund me the difference, I also have a complete new head unit for the heat coming today as well.

[00Silverado4x4]

I've been reading this topic with interest and I came up with a question myself. I work on an '04 2500 with the Vortec and one thing that was going on with that truck was all the build up under the valve covers and the hoses leading up to the throttle body. The throttle body itself was a wreck with buildup. It was also going into REP on the guy. Once I cleaned out all the junk from valve covers (including PCV orifice), hoses, and throttle body it ran perfectly and quit going into REP afterwards. Is there a possibility you may have the same build up and blockages? Just a curiousity.

[ifixedit]

I've been reading this topic with interest and I came up with a question myself. I work on an '04 2500 with the Vortec and one thing that was going on with that truck was all the build up under the valve covers and the hoses leading up to the throttle body. The throttle body itself was a wreck with buildup. It was also going into REP on the guy. Once I cleaned out all the junk from valve covers (including PCV orifice), hoses, and throttle body it ran perfectly and quit going into REP afterwards. Is there a possibility you may have the same build up and blockages? Just a curiousity.

You know, at this point I suppose anything is possible (sigh) and worth looking at if my latest discoveries don't result in a fix, thanks for the additional tip. Upon further reading the codes P0220, P1518 and P2135 could all be wiring related from the TB back to the TAC as well and may not be a faulty TB. The NAPA guy also said one of the codes (don't remember which of the 3), could indicate some air valve that's stuck open (maybe from something else clogged?) which could fall in line with your theory.

 

What's the most weird though is what the heck did my applying dielectric grease to BCM plugs last night have to do with anything? No kidding, it has had it's occasional issues before, but after the dielectric grease thing it is now possessed! I can literally say go into REP and it follows my commands! I did replace the harness with the pigtail connector at the TB recently, but I suppose somewhere deep within the harness where it goes up and over the engine something could be amiss in there somewhere. I have read of some splice inside the harness approx. located on top of the engine that could be bad. I'm still fairly convinced the now hopefully strong connections at the BCM has allowed the truck to once and for all reveal what is really wrong being it spit out the new codes today that it never has in the past.

 

I just found and read this with great interest. I printed it out and will run the tests advised while I'm in the process of installing yet another TB tonight, but this time it's a new one, not a re-man, so I will at least know (hopefully) that the TB and any of its internal parts is not the issue. There's just no way I'd be unlucky enough to get 2 bad new ones and 2 bad re-mans all in a row.

 

http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/p0220-tp-sensor-tests-1

[gmtech4]

Do you have any service info ( DTC diag tables) to follow these codes ?

[ifixedit]

Do you have any service info ( DTC diag tables) to follow these codes ?

No, but I spent some time today researching the codes as best I could on the net and it pretty much came down to either I've got a wiring ground / short issue to the TB or the TB itself is bad.

 

I'm hoping I can now bring this long drawn out saga to an end. I started tonight by following the steps outlined in the link I provided above, testing the voltage to the TB ( had 5.2 volts), the ground test (read 12.4 volts with the key on), etc., etc. All reading were right within what the guy who put the info together outlined, I finished with the ohm test on the TB and the readings were indeed a bit erratic so I concluded the re-man AC Delco unit had given up the ghost and was the culprit, so off I went with old parts in hand to NAPA for the new ones including the new head unit for the heat / defrost. The truck once again runs great with very smooth throttle response, drove it for about 1/2 hour in a variety of conditions tonight, it runs very smooth again and the best part no REP in sight so far, time will tell I guess. I also noticed ignition noise on the radio is about 90% less than before, no engine braking at all when coasting now, the idle is smoother and the slight miss at idle in and out of gear is for the most part gone as well.

 

Lesson learned and maybe I'm all wet here: If you have gone through all the bulletins, replaced all the things I have and the problem keeps coming back, start looking under the dash, at the connections to the BCM in particular (thanks wj3n for suggesting this, you may end up being the hero of the day!). My theory of the fan switch causing the truck to go into REP was likely just one of those "the straw that broke the camel's back" situations from time to time being it was in such bad shape, and perhaps with a weak or ready to quit altogether TB coupled with poor BCM contacts and a faulty switch, all it took was an occasional short of a few hot wires here and there to bring it to it's knees and induce the REP and at other times would likely just do it because it felt like it.

 

My theory is the BCM was getting intermittent or less that optimum contact at times, likely worsened by changes in temperature and humidity and the occasional good bump or jolt would also explain why at times my back doors would refuse to unlock with the FOB (they simply would not respond at all) and often the button on the armrest as well would not activate the rear door locks amongst other weird things from time to time with interior lights, two honks instead one when I locked it with the FOB and so on.

 

Also, if the BCM does indeed communicate with the PCM and ultimately the PCM with the TB, I think because of the poor BCM contacts at the plugs that this was actually over time wrecking each throttle body I installed and would likely explain why the first TB lasted 4 months, the second one about 2 months, and the third about 2 weeks as the BCM contacts worsened and then each TB would eventually just quit working correctly altogether. I'd also guess the dielectric grease at the BCM contacts finally allowed the thing to get the full contact it needed to set the codes I actually needed in order to figure out what was wrong instead of the very vague P1516 code only which doesn't really tell you much, and I like others got suckered into buying a new TAC and it turns out was not the problem.

 

Before I forget, as suggested above I also need to test to see if the fan is drawing too much power so I can potentially avoid frying another switch. I did test for noise on the radio on AM when it is on but did not notice any extra noise due to the fan running but I still want to make sure it is not causing other problems as winter is just around the corner and I really don't want to change a fan out when it's - 20 outside.

 

Not claiming victory yet but it's looking pretty good so far. Stay tuned!

[gmtech4]

you need alldata,com for $27/yr ,no brainer imo

[ifixedit]

you need alldata,com for $27/yr ,no brainer imo

Hopefully I don't have any further problems and won't need it. Otherwise my wrenching typically only involves dirt bikes, snowmobiles, and my 77 Camaro which all thankfully do not include anything computer whatsoever. When it comes to computers I'd prefer to stick to email and the internet.

 

The truck made the 28 mile drive to work this morning and ran like a champ but not holding my breath. Could just be the electrical gremlins took the morning off!

[w3jn]

Outstanding! Hope you got it licked.

 

Problems like this are the WORST, but the feeling of elation when you finally nail it is awesome.

 

I had a somewhat similar issue years ago with an '89 LeBaron (don't laugh, 40 MPG, 5 speed manual, and got 250K out of it before my ex went over a speed bump at 50 and collapsed the subframe). Anyway, came back from a trip, car was parked at the airport, and it would run for a few seconds then quit. Couldn't do anything in the lot so had it towed to a nearby shop. Guy had it 3 months and couldn't figure it out. Finally told me it was done, problem was the alternator (hah). Drove it home and the lights kept dimming. Noticed the alternator wire wasn't plugged in - I did so and it immediately died.

 

I dicked with it for a month myself and finally had an idea - it would die when the battery voltage got up to about 13. Tried a new coil and it was even worse - then I pulled the plugs and saw they were absolutely shot.

 

What was happening is because the plugs were so bad, the wires were arcing when the battery voltage was up, and creating electrical noise in the computer which got confused and shut down the engine. 4 new plugs and a set of wires, i was good to go. The feeling of accomplishment was pretty overwhelming