River, Don't want to jump the gun but this seems mostly solved. The problem at hand was that it was stuck in reduced engine power with no solution in sight. I really appreciate your help. It got my truck restoration project unstuck and moving forward again. Was figuring a 6 - 12 month time frame for the project when i bought the truck last January. ( It's a patient process. ) The very front of the truck needs some work. Was planning on replacing the front bumper & power steering cooler anyway so might as well pull the grill and open the front right up. You know ... give it all a good degreasing, inspect the entire wiring harness for damage, remake all of the ground contacts and so on. ( Whatever it needs to bring it up to spec.) It's a good bit more work and expense but it's worth it. The work holds if it's done right the first time. I might not have to go back in there for as long as i own the truck. Again ... many thanks for your help and guidance.
Pulled headlight assembly and inspected wiring in that area. No visible damage. Broke two electrical harness connectors and no sign of corrosion. (Side note: Discovered that the power steering cooler has a leak at the top. That area is a bit of an oily mess.) Pulled bulb: The truck started and shut down normally. Throttle response a bit sluggish but it was there. No power to dash cluster. Re-installed bulb: Dash cluster out, but the truck appeared to be in reduced power mode. No throttle response and truck shut down abnormally.
Sounds good. Pulling the Lo HDLP-R fuse had no positive effect. Pulling the Lo HDLP-L fuse had a positive effect. The left ( driver side) headlight & dash cluster were knocked out but the truck started and shut down normally. There was throttle response so it's probably safe to assume that the truck wasn't in reduced engine power mode.
Ok .. i went to the under hood relay center and pulled all the non-essentials one at a time. When i removed the HDLP-LOW relay the truck started up and shut off normally. No reduced engine power message and the throttle works just fine. This is the first sign of progress in months.
2004 GMC Sierra 2500HD 6.0l 4wd auto trans Awhile back the truck went into reduced engine power mode on startup one morning. I turned the key to the off position and removed it. The engine kept running and the dashboard lights flashed. Discovered that i can stall the engine with key in run position by turning on the high beams. The driver side headlight is dim with DRL running. Got trouble code U0107 Normally this would seem pretty straightforward. It's saying that there's a problem with the throttle control system somewhere. The thing is that the issue of the engine not shutting off with the key removed complicates things. It suggests that something else is going on. I originally posted this question in the wrong section as i'm a newbie here. There's a bit more background in that thread. https://www.gm-trucks.com/forums/topic/226118-stubborn-problem/ Anyway ... been going round and round with this one for awhile now. Have researched the heck out of it and tried all kinds of things but not making any progress. Maybe i'm too close to it and missing the obvious ? Maybe somebody else has seen this before ? Any suggestions on what else i might try ?
Allright ... so i pulled the under hood fuse / relay box. There's no sign of any damage to the wiring. No corrosion on any of the contacts. No sign that a critter was living in there. I pulled all of the relays and tested them just because i was there anyway. The only thing i did find was that pin 30, where the ignition relay plugs in, showed about 12.5 volts. Is that supposed to be de-energized with the ignition off and the key removed ?
Okay, i just performed a fresh diagnostic so that all of the trouble codes would be current. I used BlueDriver all systems check with engine on and transmission in park. 1 Confirmed Trouble Code U0107 Lost communication with Throttle actuator "A" control module. 2 Pending trouble codes P0141 O2 sensor heater circuit bank 1 sensor 2 U0107 Lost communication with throttle actuator "A" control module 2 Powertrain codes P0141 U0107 1 Shared Address Module Code B1440 Status: History, Power mode master input circuits mismatch 1 airbag code U1000 Status: History, Class 2 data link malfunction 2 Radio codes U1000 B1035 That's about everything that i have for now in the way of trouble codes. I've got some time today so i will go pull the underhood relay center and check for any problems there. There was evidence that something small and furry pulled out some of the fiberglass on the engine side of the firewall when it was a company truck. I think they caught that one early. Found a small nest of made of insulation under the plastic cowl that sits on top of the engine. (It might have resettled under the relay center.)
Probably is the tranny but maybe check a few basics first ? 1: Tansmission fluid level & condition. 2: Any stored or pending trouble codes ? 3: Maybe double check the transmission cable adjustment to insure that the transmission is fully seated in the drive position. (You can get some wear in the place that the cable connects to the transmission.)
Hi Guys, I'm brand new to the forum. 1st. post. I've run into a problem that's got me stumped for the moment. Vehicle info: 2004 GMC Sierra 2500 HD, 6.0l. auto trans,4WD, 44,000 miles Background: It was a company truck used for mostly plowing a paved parking lot & hauling the trash trailer to the dump. I picked it up as a project truck about six months ago. It's in reasonably good shape for it's age but needs a number of small fixes to pass state inspection. The heft of the wear & tear seems to be around the steering column. The key cylinder isn't quite right and the spring on the transmission shift lever broke. It would occasionally throw a passlock and there might have been a parasitic battery drain. It became SOP to disconnect the negative battery terminal when the truck wasn't in use. I rebuilt the instrument cluster and that apparently cleared up the battery drain issue. The problem at hand: I went out to start the truck a few months ago and it went into reduced engine power mode. I turned the key to the off position, removed the key, and the truck kept running with the cluster lights flashing. I can't seem to get past this problem. Remedial measures taken to date: 1: Checked all fuses for continuity. 2: Cleaned up every ground that i can find. 3: Replaced the ignition switch. 4: Replaced the headlight switch. 5: Replaced the TPS and it's electrical connector. 6: Downloaded the trouble codes. They relate to the throttle body TPS & transmission solenoid 7: Replaced the PCM ( The trouble codes soon returned after the passlock re-learn procedure performed.) Summary: It seems to be a power issue of some kind at this point. Maybe something is backfeeding ? Maybe something that controls the power is sending it in the wrong direction at the wrong time ? Could it possibly be the BCM ? At this point i'm leaning toward wear & tear in the ignition lock cylinder & ignition lock cylinder housing as being the culprit. Maybe the gearing in there is worn and not engaging the ignition switch correctly ? I wish i knew more about how it all works. Could really use the advise of someone that works in the trade every day and has seen this problem in the 2004 model range trucks before. Maybe there were some TSB's released on the issue ? Any help would be sincerely appreciated.
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