nateg20

Update: Water pump was the point of failure. The oil substance in the wheel well was the dex coolant, which there is none of that left in the overflow anymore. Engine hasn't really lost any oil, but it smells very burnt. No signs of water in the oil.

I made some bad decisions and believe I destroyed the 6.2 in my 2020 AT4 with just over 86k miles. The truck was great, it didn't use/lose any oil, had good power and got ~19 mpg. It was after midnight. I was 11.5 hours into a 12 hour drive with the family riding along and saw the finish line. It told me that I should pull over but I didn’t believe it because the warnings were just instant and it wouldn’t let me see any real data. Unfortunately I didn't make it. Lots of smoke from the tail pipes, and sprayed oil all over into the drivers side wheel well. It still starts but sounds horrible and blows white/blue oil from the tail pipes. On the side of the road I realized all of these warnings were because it had blown the serpentine belt off for some reason. Bottom line, I severely overheated the engine. I sent it to a local shop and am unsure of the exact condition of the engine at this point. Hope to know more on that this coming week. I’m pretty confident I’ll need to replace the engine. No warranty of any kind so I’ll be funding this replacement myself. IF my existing engine doesn’t have any new external inspection ports or other signs of block damage I believe the most cost effective option is likely to get a GM 19420611 remanufactured engine and have the shop swap it out while hoping that I get most of that $7000 core fee returned. That core fee seems like a huge gamble at this point. If the engine has any signs of damage (ie where did all that oil come from?!... maybe the oil cooler/ cooler lines?) I’ve been exploring other options to replace the engine. The first option that comes to mind is finding another L87 from a salvage yard or from eBay. This option only seems viable if I’m sure I won’t get the core fee returned as these engines seem to have a premium price tag. In addition I’ve now got an engine with an unknown history. Rolling the dice. A slight improvement from this option may be getting a reman L87 from a vendor other than GM. This price seems competitive with salvage yard engines with better warranty. I’m referring to vendors such as spprecision, michiganmotorz, fraserengineco, accurateengines, promarengine, and perhaps jasper. I have no experience with any of these companies and do not know how long they would take to ship. Many of them claim to have some in stock. All of the other options almost certainly require giving HP Performance a fair amount of money to get a tuning package. I’ve always been quite skeptical of the DOD on this engine but it really hasn’t caused me any sort of issue. It would be nice to be able to build a reliable engine and gain some power but I put a fair amount of miles on this thing and would like to continue to do so. I’d probably want to go straight to deleting the DOD and would be ok with losing a few mpg in order to gain reliability. I do not even know what options are available and or feasible. I believe all of the GM 6.2 crate engines with direct injection also have DOD. So that means I couldn’t go with a GM 19435108 (6.2, no DOD). The only non DOD gen V engines appear to be the 6.6 cast iron block versions. Maybe an L8T with a cam? AKA L8P. Keeping all of the OEM truck functionality (IE keeping GM Global A happy) with any engine other than the L87 seems like a daunting task for even an experienced tuner which I’m not sure that I’ve got access to. Sorry for the long message, I sincerely appreciate you reading this and really hope somebody who has read it has some insight that I presently do not. Thank you again. To summarize, if your truck tells you to pull off the road you should listen to it. Don’t be like me. It seems like a very poor time to damage an L87 engine.

Thanks bamorris2 for sharing this new TSB. I got these CEL codes a few weeks ago. At this time I read a TSB similar to bamorris2 's post (but not nearly as detailed) and interpreted it as if the TCM sees a wheel speed before it thinks it should (or after apparently too) it "disqualifies" that sensor, then the bus disqualifies the controller. Must re-qualify it pretty darn quickly though. I suspect this check is occurring when the systems are initializing (starting the engine). I realized I was slamming the truck into gear right after pushing the start button, especially if it was already warm. For about the past 2 weeks I've really tried to let the gauges sweep on every start before I put the truck into gear. So far, since then no CEL. My BT scanner read this CEL twice within a week. But to prove or disprove my theory folks getting the codes, maybe try letting the gauges sweep during startup before putting it in gear and see if the codes go away. Maybe even set the park brake every time you turn it off too. ============1============== U0101 Raw code: C101 ECU: 7ED Status: Pending OBDII: Data bus, transmission control module (TCM) - no communication GMC: Lost Communication With Transmission Control Module Invalid Data ============2============== U0100 Raw code: C100 ECU: 7ED Status: Pending OBDII: Data bus, engine control module (ECM) A - no communication GMC: Lost Communication With Engine Control Module Invalid Data; Lost Communication With Engine Control Module Message Counter Incorrect; Lost Communication With Engine Control Module Bus Signal Checksum Error ============3============== U0146 Raw code: C146 ECU: 7ED Status: Pending OBDII: Data bus, gateway A - no communication ============4============== P25A2 Raw code: 25A2 ECU: Engine control unit Status: Pending ============5============== U0101 Raw code: C101 ECU: 7ED Status: Confirmed OBDII: Data bus, transmission control module (TCM) - no communication GMC: Lost Communication With Transmission Control Module Invalid Data ============6============== U0100 Raw code: C100 ECU: 7ED Status: Confirmed OBDII: Data bus, engine control module (ECM) A - no communication GMC: Lost Communication With Engine Control Module Invalid Data; Lost Communication With Engine Control Module Message Counter Incorrect; Lost Communication With Engine Control Module Bus Signal Checksum Error ============7============== U0146 Raw code: C146 ECU: 7ED Status: Confirmed OBDII: Data bus, gateway A - no communication ============8============== P25A2 Raw code: 25A2 ECU: Engine control unit Status: Confirmed