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Im at a loss...

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Old July 13th, 2018, 3:00 AM
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Hello everyone, New to the forum and am hoping that I can get some help with an issue that has me completely at a loss. I made a post a couple days ago but I guess something went wrong and its gone, idk... Customers Vehicle is a 2003 Suburban 5.3 Vortec, 4x4 z71 with all the bells and whistles. The issue I am having with it, began with a complaint that the PRND321 selector display had gone out and the high bean indicator stayed on and flickered when the headlights were not in use and the display for the radio would come and go. Shortly after this problem, the owner complained of a high and rough idle 1 day before the vehicle set multiple codes. Codes were as follows: P0120, P0220, P1516, P1518, P2135. So I begin researching on the www and come to the conclusion that its a grounding issue. So I start digging in the wiring harness to locate the ground for the TPS, discovering that a rodent had gotten up into the engine bay and chewed 2 wires going from the TAC module to the TPS, 1 wire from TAC to ECM, and the B+ wire on the left of the fuse block, and a little bit of the B+ on the right side. Wonderful. So I repaired all of these wires with rosin core solder and polyolefin tubes. had to put a 3 inch extension on one of the wires, cant remember which though. Thought that was the fix, but no. All codes remained. So I figured the rat must have caused a short to the tps, so I replaced the TPS and its pigtail appx. 12" back into the wiring harness. Clear the codes and it fired right up and ran great. Took it for a test drive, and on my way back to my shop it died on me and threw a code, started right back up though. Scanned it again to find P1518, P0220 and P0120. So I replaced the accelerator pedal sensor and inspected the wire harness leading from aps to the TAC module. In doing so, I noticed a burned wire smell coming from the TAC module, so I removed it to be sure the smell was coming from it and confirmed it was, especially if I knocked on it. So I replaced the TAC module and double checked all of my soldering work. While re checking the wires around the fuse block, I decided to have a good look see under the block to find some serious corrosion and burn marks on the underside of the block. I then replaced the entire fuse block,disassembled the old one to have a look see out of curiosity and found burned and broken circuit wires inside.This rat really did a number on it. Reassembled everything again, and decided to relocate the TPS ground to a more convenient location on the front of the engine, as well as adding a new ground strap from the drivers side block to firewall and added another strap cause why not. I located the 3 grounds under the drivers door on the chassis and cleaned those up real nice, and cleaned the B+ mains to chassis and block as well. During this time, the info display on the instrument cluster went out, and I read that the original complaint of the PRND321 display going out was a sign that the cluster was failing. Replaced it. After all this, you would think it was done, but you would be wrong... I started it up, and it ran great, but I was skeptic. So I shut it down and re started it, and it ran great again. I did this about 20 times before the "Reduced engine power" showed up again and it threw P1518 and P0220 again, and no response from the accelerator pedal, as usual. The weird thing is, if I clear the codes, it starts up and runs great again. Until I shut it off, then maybe the code will come back, maybe it wont. It is totally random. I am going to limp it to a dealership and have them test the ECM and make sure it is functioning properly as well. I am at a loss, and am hoping someone can give me an idea or something to go on. Help?
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Old July 13th, 2018, 3:18 PM
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My guess is the ecm. The prndl cluster is a given issue with the dash lights, you can get that updated with sending in your cluster, due to the odometer. Since I read your post, seems you have electrical experience. I'd recommend on the 1518 with an ohm meter, check the variable resistance from the throttle actuator, could be, even new a problem with it. I'd try checking it for linearity at 0-1/4, 1/2, and full stroke.
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