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Dec 19, 2013
Fort Worth, Texas
Oh well....Someone got to fix 'em crzy 2004 Chevy Suburban 1500 Flex Fuel, 5.3L/4L60E. Was bought buy one of my car lot clients, Said he got it for scrap value. Pretty clean with new tires & only 86,xxx miles. *Compliant is that it's doesn't run, He tried to start it with a jump box & it won't even crank. *Of coarse the battery is beyond dead, So I put a charger on it for a couple hours while I handled other business. *That's when I noticed a bunch of Foil Tape on the ECM, And I mean a BUNCH, Like 2 rolls of it!! Here we go! *I also noticed a piece of Romex, Prolly 2/10 spliced into the harness & running under the throttle body over to the Refrigerant Pressure Sensor. *The Low Pressure Switch & Coolant Temp Sensor have butt connectors. *Got the battery up, And the battery is only a few months old BTW & passed a load test with flying colors. *Hooked up my trusty Snap-on Solus Ultra to read DTC's, No communication. Replace blown Cigar Fuse. *Has a hard P1631 which means the Vehicle Anti Theft Password is incorrect. Tech Tip....Always check the VIN in the ECM & make sure it matches the Vehicle VIN! The VIN's did not match, BUT it was a 2004 Flex Fuel 5.3L ECM & only the last sequence numbers didn't match. With the VATS active it will not crank. *I have HP Tuners & unlimited credits for 2004 Gen III truck ECM's...."F" IT, I'm not going to spend money on GM SPS (reprogramming the ECM) when I don't much of anything about this truck!! So I hooked up HPT to it & simply turned the VATS off for now. *Truck starts & runs fine with no check engine light, No current or pending DTC's, Can it really be this easy? *Took it for a test drive, Nope...Not going to be that easy! Transmission doesn't shift out of low gear & the Speedometer is inoperative along with no VSS reading in scan data. *Turn around, Get to back to the shop & jack up the back wheels. *Need to access the ECM connectors, That when I get to cut 2 pounds of foil tape off the ECM. Not real enthuzed at this moment & didn't get a picture of the mess. *Find a T-Tap on one of the ECM Battery hots & it's jumped (Unfused) over to the Alternator/Jump Start Junction. Okay I'll fix that later as it's not currently smoking or on fire LOL *Removed both ECM connectors & noticed the plastic Pin Locks/Pin covers stayed behind in the ECM. That's different! *Locate the 2 VSS circuits & unpinned them from the ECM connectors. *Dug the Pin Locks out of the ECM & did a quick visual scan of the ECM pins for being bent, Didn't see anything obvious. *The plastic tabs that hold the Pin Locks to the ECM connectors are broken & figured that's why they stayed behind in the ECM. No big deal As Long as you put them over the connectors BEFORE engaging the connectors into the ECM as they act as a guide over the pins. *Hooked my Snap-on Vantage Pro up to the VSS circuits, Set on A/C graphing scale. This is a A/C Sine Wave VSS sensor that produces it's own voltage. Put the truck in drive & the sensor produced a nice A/C waveform that increased in frequency with driveshaft speed. *Performed a "Pin Drag Test" on both VSS circuit pins & it passed. *Moved the harness around & watch for a drop out in the signal....None found. *At this point.....I'm thinking that it's possibly the PCM & I absolutely HATE that as a conclusion to my diagnostic approach. The fact I've never seen this exact issue with a Delco P59 controller makes it sting even more as I know them so well. *I need some coffee & a break from this pile, So I ran up to QT for some brain fuel. *Decided to examine the ECM further with some good light, Which is fluorescent for my eyes. LED tends to be a little to bright & concentrated. *That's when I saw that some of the ECM pins where pushed straight back into the ECM.....WOW. It takes a lot of force to do that & theoretically should have pushed the connector pins out & broke the flimsy plastic tab locks! *Took the ECM apart & pulled the pins back out to their original position with a pair of hemostats. Had to solder up a couple broken joints on the board as well, One of them being a VSS circuit. *Further inspection revealed that the Pin Locks were mangled up pretty good on the "Key Slots"....What prevents trying to install the connectors in the wrong slot/position. Fixed them with a razor blade. *Had to fix a couple pushed out pins in the connectors that I found after looking closer. One lock did fold over like I thought would happen instead of pushing the pins back into the ECM. *The jumped hot wire was added because the PCM-B fuse was blown. And T-tapping in a unfused wire was easier than replacing a fuse??? *Test drove the truck again, Trans shifts great & the speedometer works. But WAIT....That's not all!! *It was kinda warm today & the A/C didn't work.....It will be right back in my lap if I don't fix it now! *Scan data revealed that the Refrigerant Pressure Sensor was reading Zero PSI, Hooking my gauges up showed 100 PSI. Not really surprised as this is where the Romex is spliced in. *I so happen to have a 2004 Silverado engine harness, I peeled the Refrigerant Pressure Sensor circuits out of it instead of making new ones OR putting at least 6 splices in the original harness just to most likely run into MORE issues. The Silverado harness had already stripped of it's split loom & tape so it was pretty easy! *Run the new Refrigerant Pressure Sensor harness along it's original path after split looming & taping it up. *Try to start the truck.....Will not start, Just cranks! *Scan tool reveals 20-30 DTC's, Listing them wouldn't be helpful! *Unplug the Refrigerant Pressure Sensor & test the voltages & their fine. *Left the Refrigerant Pressure Sensor unplugged, Cleared the DTC's, Truck now starts & runs with no DTC's. *Long story short.....The Refrigerant Pressure Sensor is internally shorted thus bringing down the 5-Volt Reference network. *Upon further investigating.....The Romex hack was actually wired correctly & should have brought down the 5-Volt network just like my replacement/patch harness did. BUT, They used a connector off something else, I know this because the wire colors were wrong. The connector terminals was so heavily corroded with green crusties that it didn't make contact with the Refrigerant Pressure Sensor pins. *New Refrigerant Pressure Sensor fixed the short, Then I found the A/C Compressor relay missing, Replaced that....Now has ice cold air! I believe that the shorted Refrigerant Pressure Sensor is what got this whole MESS started in the first place, To bad I had to work backwards through all the hacking to find it. Not to worry because I OVER charged for this one!!!!!!!!! Pushed in ECM pins..... [Linked Image from] [Linked Image from]
Wow. Remember when we had points and carburetors? Now-a-days you almost gotta be a electrical/mechanical engineer to work on these things. Romex.......... duh Awesome job clinebarger!!! You have the patience of a Saint!!!
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Originally Posted by FordBroncoVWJeta
I wouldn't even had wasted my time on that truck. That sounds like a complete nightmare!
I know that back in my consumer car repair days, after awhile I liked a challenge. I suspect that's true of lots of Mechanics. It keeps the work interesting.
In the late 80s we had trouble-cars like that in our shop (as the support for the engine management supplier). I admire your tenacity. The worst we had, which the dealer and factory couldn't fix, weren't even ¼ as bad as the one you described! And we had all the components flying around for try and error. I wrote checking procedures. I admire the people who worked on that car until you got it. They definitely had a strategy... Just not as strong as yours. Like a weak chess player vs a good one. My first post. Greetings from South Africa!
Originally Posted by oldhp
Wow. Remember when we had points and carburetors? Now-a-days you almost gotta be a electrical/mechanical engineer to work on these things. Romex.......... duh Awesome job clinebarger!!! You have the patience of a Saint!!!
And this is an ancient 16 year old vehicle. Systems now are 100x more complex. I have spent entire days working with nothing but an oscilloscope and break out box.
Great work! Jobs like that can really go on your nerves but they have to get done. I am facing a similar horror trip with a Saab that someone hacked the wiring because they didn't have a Tech2 and started cutting wires trying get things to work that had been turned off in the system. Its going to be a huge PITA. On these cars I use a Tech2 to change the VIN in the ECM to install parts that have been previously used in another vehicle, you know the divorce and marry parts to this ecm by VIN or they are not recognized thing, would the Tech2 change the VIN in this truck also? Do these US GM vehicles require security access to change some settings also?
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