Marleay

Sorry no pictures of the filter. However the main clue was how heavy the old filter was - as if it was full of sand, for reference sakes. The bottom of the pan had sludge from the plates.

To wrap this post up for future reference: the apparent problem after changing out the oil sensor without any change to the original issue was a clogged transmission filter. Although the fluid level was ok, colour seemed good and did not smell burnt - when we dropped the pan to drain the transmission fluid we found a clogged filter. When the filter was replaced and new ATF was put in the truck is now running normal. The MAF sensor solved one problem. The oil pressure sensor solved another but it was a lack of regular transmission maintenance that caused the now not-so-baffling issue. Thanks for the help.

Yeah fascinating.

I thought maybe the torque converter originally but the guy at the transmission shop said that torque converters either work or they don't - I wouldn't be able to drive for 2-3 minutes and then it start free-wheeling. He suggested checking for flow at one of the cooler lines. One thing to add is that if I start the truck and leave it to warm up for a couple of minutes and then get in to go it will be already in the free revving mode and won't move. Seems more like a time based problem than a driven mileage one.

At this point there no codes except the oil sensor failure. All other modules scanned come up fine.

Okay, totally understand that. I think it comes down to 2 separate problems. In the past few months the truck was running rough. Pulling up to a stop the revs would go down and then surge causing the truck to move forward. Daughter complained but nothing was addressed at the time. Service engine light was on. Last week she phones to say that the truck starts and runs but then won't move when in gear. I have her bring it to the shop and put a diagnostic reader on and clear codes. Codes were symptomatic type i.e. intake, combustion, exhaust out of range. Cleared codes. Test drove it. All drive fine for 2 minutes or so and then acts like trans in neutral. Codes that remain are MAF sensor and oil pressure sensor (shorted). Replaced MAF sensor. Put injector cleaner in fuel. Engine runs fine but after 2minutes it is all revs and no go. Shut engine off. Start again. Runs and accelerates through the gears ok for about 2 minutes. Repeats the same sequence over and over again. So MAF was one problem which I think is fixed. Engine starts and runs smooth now. Lack of motion after a couple minutes is the baffling conundrum now.

I haven't changed the oil sensor yet. It is in a bit of bad place on the 4.8L engine so I'm putting that off to last. I have all the fluids to do the transmission and both front/back differentials now. will try to get to that in next 2 days. I don't drive the truck so I don't know when the sensor/gauge started acting up. it is an input to the engine management system so maybe there is an output that causes these symptoms. The baffling part is the engine revs to redline without an issue during this problem. I would have thought the ECU would have limited the engine revs in 'limp' mode and let the vehicle limp home.

What surprises me is that I've talked to a mechanic and a transmission rebuilder and now posted here and nobody seems to have heard or seen anything similar happening to a GM truck. The exception being a brother-in-law who had similar happen to him and the fix was the ignition switch.

The oil gauge is pegged at high. Diagnostic said the oil pressure sensor was "shorted". I've tried the drivetrain in forward, reverse, 3,2,1, 4WH and 4WL. I thought maybe the torque converter but that was eliminated from the driving tests. I'm not a mechanic but grew up fixing what I drove.(1963 Ford Fairlane 2 door Sports Coupe was my first car) Dad was a petrolhead in England and would build full cars from bits and pieces after the war. I have an electrical contracting company now. Jack of all trades...master of some!

Thanks for the late advice...I was feeling around in the area a couple of days ago and now have scratches from knuckles to half way up my forearm! I have all the tools and the 1-1/8" deep socket but waiting to change the sensor. I need to get the running problem figured first. Ive had/have lots of GM vehicles and never experienced a 'limp mode' with any of them. My only experience with that mode was in my Mercedes Sprinter van RV with turbo diesel going over the Coquihalla highway pass coming out of Vancouver. Minor issue but a big tow bill!

Having trouble typing replies on this site... really bad lag. I have a good diagnostic code reader with Bluetooth connection to iPhone app. No codes from any modules. I have the oil pressure sensor which I will change out but it is in a hard to reach place. I can't see that causing the problem but the gauge doesn't work so it is worth replacing it.

Thanks. I think it is an aftermarket auto starter and it did have an alarm system installed as well. We don't use either of those but there is some wiring under the dash associated with those systems. The truck was one my company trucks that got passed on to the kids - so had it for a long time, almost since new. It was running rough and some of the original codes were to do with tht The new MAF sensor fixed that. My guess is that it is the main ECU but I have a diagnostic code reader

2006 Chevy Silverado with 4.8L V8. Daughters truck. She calls and says the truck is revving but hardly moving then if she turns off the engine and starts again it runs fine for a minute or two and then goes into 'limp' mode and then like it is in neutral. I put a code reader on and it had some codes. I cleared them and then was left with MAF sensor issue and oil pressure sensor failed. Replaced the MAF sensor. Still have problem. Someone suggested the ignition switch so I replaced the ignition switch module (not the actual key part). Still have problem. Transmission fluid is up, looks and smells fine. It also does a strange thing when reconnecting the battery - the engine tries to start and dies on its own 3 times - scary when it happens! Help please...