HDET Mechanic D

From my research there many people one gm forums that have brought their truck into the dealership (for months) for this issue, they changed the battery, starter, underhood fuse panel, the fuel pump module, the steering column module, ignition switch, harnesses and they still don't have it fixed.that video above is another perfect example of a the dealer doing the parts cannon to troubleshoot. The result is the customer is frustrated about wasting there time/ not having a truck, the dealer and engineering are scratching their heads on an issue that is labour intensive to figure it. Thats why I will never bring my truck to the dealer. If you ask chatgpt which is the most unreliable truck for every year from 2019 to 2024, the answer for every year is the gmc/chev 1500. Ford doesn't use corrosion prone ground straps. For those years the f150 was at the top of the reliability rankings. So what is the solution to all these problems? Having a truck that didnt want to start start 50 times in 4 years with 85k km of ownership has left me severely regretting choosing a brand that I thought was reliable at the time of buying it.

GMC Bullitin for ECM wire rubbed out.pdfThe screen shots above are from that bullitin here.

I fixed all my problems Cleaning the fretted ecm connectors definantly fixed my issue.Basically because they put the truck together with no dielectric grease from the factory. The vibration between the unlubricated male and female ECM terminals cause wear, which caused dust to accumulate between the contacts (this dust is only visible in the first close up pic). That dust is the resistance that caused the bad connection when it was cold. I had no issues starting repeatedly for 2 weeks at -20C to -35C after I only cleaned the ecm male terminals and replaced the ECM Ignition relay. My starting success rate was 10% before doing that when it would be colder than -20C. See the pics of the brutal terminal fretting. here. https://drive.google.com/drive/folders/1XUT38ks-bXoX2nkBImeKDQfxghTkoD82?usp=sharing I found more issues with my truck bellow which would of caused me to loose my power steering and brake boost due to my severly corroded ground which had 84000KM (on my 2019 just like in the video ) on it in the salt belt (theres a bulletin on this) For anyone that wants to see pictures of the ECM harness MOD I did (reroute so it doesn't wear/ hydraulic hose wrap mod), every ground location in alldata diagrams, the new weather resistant ground straps I made to replace the gm corrosion prone straps and the location of my corroded ecm wire, check out my google drive pics link. https://drive.google.com/drive/folde...XI?usp=sharing I drilled a few holes in the ecm plastic mounting bracket to feed zipties threw the holes to secure harnesses to the ecm bracket that were previously just wearing on the bracket previously due to the poor routing (its the oem way) of the harness. The corroded grounds behind the right front fender liner are well hidden as I never spotted them everytime I was under the truck with it on the hoist since owning the truck. Thanks to silveradosid in helping me resolve this problem. Both straps were corroded, Engine to cab and Cab to Frame. See the all data pics for exact ground locations in the link above. I spent 2 days inside the engine bay with the airbox out, taking apart the ecm harness, inspecting for opens, soldering the coroded ecm wire for ECM switched ground for HIGH speed cooling fan (temporary fix), putting the ecm harness back together properly, securing the harness, so it wont wear on anything. The loose wires inside the harness are now taped tightly together .If I have anymore issues I will be buying a new ecm harness.which is arround 750 CAD. The problems I noticed with the GM's jackpot ECM/TCM/ FAN harness routing are: After 4 years of driving, the engine harness cable trays succured to each stut frame mount on both sides of the engine, were unsecured flopping arround with every bump, all the zipties holding the harness to the black plastic cable trays were loose.Meaning the harness was free to move with the cable tray that was free to move. There were rocks between the harness and the cable tray poking at the harness.This didn't seam to cause any damage to the harness, I have not opened that up yet for inspection. I used flange nuts to tighly secure the cable trays to the existing studs from the stut mounts (see in the pic). I used hydraulic hose wrap on the cables in those trays and anywhere there is a jackpot of harness that can wear everywhere. I rerouted the Fan harness from the ecm harness so it can't wear, also secured it to the ecm bracket (made holes in it for zipties). The octopus jackpot section of the ecm harness next to the ecm was taken apart for inspection. I noticed none of the wires were tighly taped together inside the harness bundle. Which is no good considering that the harness is always getting tugged on when the engine torque raises the engine/flexing the engine mounts, pulling on the harness which is connected to a fixed frame object (ECM). The fan harness wore on the corner of the plastic ecm mounting bracket. The chaffing from 4 years of driving did not penetrate the tape arround the harness, it caused the loosely danging wire inside the harness to wear and corrode severly a wire which was the switched ecm ground that sends the High speed signal for the cooling fan. (no code for this ever) The ecm mount seemed quite flimsey/to flexible (maybe so it flexes when the engine pulls on the harness?) which was likely causing more vibration between the ecm and its harness terminals.(possibly why my ecm male terminals were fretting) I used a HD strap pull the ecm down tighter to the frame. Great spot for an ecm, gm will probably save a billion dollars in recalls if there is no data log to investigate for crashes caused by something that would require a recall . The ecm is behind the bumper, it will likly be immidiatly be destroyed during frontal impacts. I took apart, cleaned and inspected the ecm/ tcm connectors, all other connectors nearby, and applied dielectric grease (since it was assembled with no dielectric grease in mexico) which should prevent any future fretting between terminals. I learned that fretting is caused by not using dielectric grease. Every ground underhood was installed on a painted surface. I removed the paint and cleaned and dielectric greased every under hood ground. After I did all that. While driving, I noticed the OBD voltage is no longer all over the place, no longer noticably lower in voltage than all the ecm ignition voltages and all the ecm ignition voltages are not irratic anymore. The truck cranks a bit faster and I have had no codes or cold starting issues at all now. I will be cleaning the grounds in the cab and checking out the BCM connector pins for corrosion/fretting as salty winter boots are constantly bringing in fresh salt into the cab.

ignition switch has gone down to 4 volts while cranking. https://drive.google.com/file/d/1hKHaxVVgkPPGSsFp4RUj5-T505kh6EOZ/view?usp=sharing BTW, this is above is normal. RTFM! This is looking at the ecm while trying un unsucessful remote start https://drive.google.com/file/d/1XdMIVrnz-VvjkFSGfI135NiN_A--XMyL/view?usp=sharing

I have been getting some help from justanwsers Known Issues and what the gm tech told me to check. Fault Codes that were always the issue before and not now after trouble shoting: Active: P2535 U0100 as of today Pending: none as of today New codes that are the only ones active after troubleshooting are : p2535,U0100. Now after disturbed the entire ecm harness, cleaned all the pins of the ecm, replaced K77 (ECM IGN) and K70 (starter). There still is No CEL but there are still 2 different active faults that I was not getting before and now am consistently getting (p2535 and U0100). The pending faults from 2 days ago are gone. Triggered Conditions: Fault occurs only below -20°C and starts with a remote start attempt or just a manual start attempt. Past Troubleshooting: Extensive testing of ECM connections, voltage, continuity, harness inspections, and replacing relays. I also suspect issues related to aftermarket modifications, though these seem unlikely. Suggested Steps by the GM TECH 1. Focus on Key Wires During Fault ConditionsSince the ECM is comparing its battery feed (B+) to multiple ignition feed voltages, you'll need to monitor: B+ Wire at ECM: Confirm consistent voltage at all times. Ignition Wires (IGN): IGN1, IGN2 (common in GM vehicles). Trace specific ignition wires referenced in the service manual or circuit diagram. Use AllDataDIY or a factory wiring diagram to identify which IGN wires the ECM monitors. Monitor these with back probes while duplicating the fault (cold start conditions, -20°C or below). 2. Address New Fault Codes P2535: Likely related to the ignition switch RUN/START circuit. Check if the ignition voltage fluctuates under colder conditions. This aligns with potential ECM comparisons. U0100: Loss of communication with ECM, which may indicate harness issues or power supply interruptions. P0685: ECM/PCM Power Relay Control Circuit. P0700: Generic transmission fault indicator but might stem from the same communication issues. P25A2: Secondary fault, possibly tied to voltage discrepancies affecting modules. 3. Inspect and Test Specific Components ECM Harness and Connections: Focus on the 6 inches of ECM harness you haven't inspected. Inspect for micro-chafing or cold-related expansion/contraction causing intermittent faults. Battery and Grounding: Test and clean grounds (G114 and others relevant to ECM). Use a thermal imaging camera (if possible) to identify weak connections under load. Light Bar Wiring: Disconnect completely, even if unlikely. Aftermarket accessories can introduce unexpected behaviors. Relays and Modules: Test the BCM and ECM modules for updated software. Check BCM software versions, as per TSB PIT5735B. 4. Advanced Testing ECM Live Data: Monitor ECM ignition voltages and compare them with expected values during cold cranking. Use a diagnostic scanner capable of live data during fault replication. Voltage Oscilloscope Testing: Use an oscilloscope to observe voltage stability on IGN and B+ lines during remote start attempts in cold conditions. 5. Evaluate Software Updates Even if the BCM and ECM updates seem unrelated, apply them if available. Some updates address intermittent faults that aren't explicitly documented. Plan for New Codes TroubleshootingWhen you return: Disconnect the light bar. Back probe IGN wires during cold cranking attempts. Test the new fault codes systematically: P2535: Ignition switch testing and voltage at ECM RUN/START circuit. U0100: Harness inspections near ECM and modules. Replicate the fault with ECM harness slightly disturbed to rule out latent mechanical wiring issues. Next StepsIf these steps don't isolate the issue: Consider ECM replacement under the powertrain warranty. Perform a dealer-level diagnosis to rule out any advanced firmware or hidden issues. Today, 7:12 AM I was looking for a ground on the right front when I was under there. I will check that out first thing when I get back home in a few days. A ground issue would explain all these random codes. I have only confirmed G114 has no issues underload in a warm garage. But maybe when its cold its having contact issues. There is a ground strap behind the right front wheel liner that I haven't found and checked yet. Okay so Its pretty rare in the last 2 months that my truck starts with out any issues when its colder than -20C.(like maybe 1 of every 5 start attempts it will start with out any issues).So thats 2 cold starts in a row at -37 that it fires right up with no issue.So I'm starting to think I may have done something to improve this problem I did noticed when running the truck this morning that The ECM (42) Voltage was at 15.53V and the Obd adapter Voltage was all over and would go down to 15.1V. Looking at the ecm Print again I noticed I missed one ignition feed (accessory wake up serial data circuit wake up voltage). Which is pin 33 of X2 at ECM. The BCM sends power to wake up the ECM and TCM when the Ignition switch is put in ACC or RUN position or fob start is requested. I don't think its relevant because if their was a an open or short it would throw a code for that circuit. I did once get U0101 and U00146 in the past. I didn't look them up yet.But I will. Which exact IGN pins do you want me to back probe, their are many (10) on X2,X1. Or back probe and monitor all of them. I wasn't completly certain which IGN wires the ecm are actually comparing to B+ to determin and trigger the fault. I would assume (hate doing that) its the wires stated in the DTC guide I attached which are 14,15& 16 on X2 at ECU and 48 and 49 of X1 at ECU. Today, 7:23 AM I will do everything the tech stated. I have not actually looked at the troubleshooting guide or troubleshot the new active codes yet. p2535 and U0100. Those are the only 2 active codes I have now. .I am sourcing out a GM MDI2 and GDS2 software as I will likely need it if I want to be able to keep and fix this truck. So you want me to test the ignition switch when its cold and when the codes are active.There is a section of ECM harness I have not inspected yet. I must removed the airbox to do the complete inspection properly. I will bring it to the dealer asking for the Latest ECM and BCM update. I know they updated it probally 2 years ago so I'm sure there is new versions. I will completly disconnect the light bar from everywhere. I want to buy a scanner if there is one that allows me to see all ECM inputs and output of every wire. Autel Maxisys Ultra or Lunch 432 Pro or elite may allow me to do this but I am currently looking into this. I have a Oscilloscope on my 24 hour data logger blutooth multimeter that I will use to to backprobe the ecm. I was quite rough with the 6 inches of harness from the ecm while continuity testing. but beyond that it was to well secured to pull and bend it or even see it. I must remove the airbox next to shake test/ inspect it properly. I think I must readjust my troubleshooting guide towards the 2 new active codes. Your response was very helpfull. to perform a Perform a dealer-level diagnosis to rule out any advanced firmware or hidden issues. I must have GM diagnostic software and hardware to really do this step correct? If so I may have to bring them the truck. I looked up all of those active codes That i did have in the past, all loss of communication of each modules. U0284 Airshutter Module, U0101 TCM, U0146 Serial Data Gateway Module. They probabbly all have a a common ground that could be bad. I have not cleaned any grounds yet. Just sprayed 2 with fluid film.

Thank you for suggesting that to me, I was looking for a ground on the right front when I was under there. I will check that out first thing when I get back home in a few days. A ground issue would explain all these random codes. I have only confirmed G114 has no issues underload in a warm garage. But maybe when its cold its having contact issues. Okay so Its pretty rare in the last 2 months that my truck starts with out any issues when its colder than -20C.(like maybe 1 of every 5 start attempts it will start with out any issues). So thats 2 cold starts in a row at -37 that it fires right up with no issue.So I'm starting to think I may have done something to improve this problem. I disturbed the entire ecm harness, cleaned all the pins of the ecm, replaced K77 (ECM IGN) and K70 (starter). There still is No CEL but there are still 2 different active faults that I was not getting before and now am consistently getting (p2535 and U0100). The pending faults from 2 days ago are gone. I did noticed when running the truck this morning that The ECM (42) Voltage was at 15.53V and the Obd adapter Voltage was all over and would go down to 15.1V. Looking at the ecm Print again I noticed I missed one ignition feed (accessory wake up serial data circuit wake up voltage). Which is pin 33 of X2 at ECM. The BCM sends power to wake up the ECM and TCM when the Ignition switch is put in ACC or RUN position or fob start is requested. I don't think its relevant because if their was a an open or short it would throw a code for that circuit. I did once get U0101 and U00146 in the past. I didn't look them up yet.But I will.

Can I post all the relevant Pdf technical service bulletins and all data troubleshooting docs/ schematics that I used to trouble shoot with out violating any forum rules? My intention is to help anyone else by providing the resources I have used. As well as provide the schematic for anyone else that wants to look at and peovide their thoughts.

These are the codes I would get every year when its colder than -20c. There are some random codes but p1682 active and pending p16a7 and p16bc are the codes that always come up everytime i I get a crank no start fault.

These are the new codes I cant clear after all the trouble shooting. 3 days ago. Most are gone now, Its just P2535 and U0100 That are left active now.

1GTR9CED3KZ198419 2019 gmc sierra 1500 new body 5.3 double cab. : The code I get is basically the ecm comparing its battery feed to its multiple ignition feed voltage, If there is to big of a voltage gap it will trigger a code and I get a crank no start condition. This usually starts when I try a remote start which triggers the code, then I try manually starting it which I then get a crank no start and a Cel that appearsafter the remote start attempt. The condition is: for the last 3 years, any time it gets colder than -20c. I get a ingition related code which causes a crank no start condition. The cracking will always be fast ( like there is a good battery reserve), and when I press the start button, it will get stuck cranking for as long as possible, till I repeatedly press the start button multiple times to get it to stop cranking. Its not due to a low battery as I have a charger on the battery the whole night charging the battery and the problem will still occur. And every time its warmer than -20c, I never have any trouble or any codes. Meaning in the last 3 years, every winter i have this problem and same codes and every spring summer fall (3 years) I have no codes and no problems. Every winter when it gets colder than -20C, I would get these same DTCs: p16a7 would always be active and these 2( P1682,P16BC) always pending when the fault occurs. Recently the problem has been more frequent, and a new condition has occured: no crank no start after hitting start ignition button after multiple attempts. To resolved this new condition that only happen once at-30c, I disconnected the battery and reconnect it and it fired right up no starting issues with the cel then going on. Other times it ooccured, if I would just let the truck sit for 5 mins (after a failed attempt to manually start it), it would fire right up with no issues and CEL would then go on with those same 3 codes (active: p16a7, pending:P1682,P16BC) I have used alldatadiy D16a7 dtc troubleshooting guide, and 3 relevant technical service bullitins to extensivly troublehoot this problem. I have run out of things to check for litterature for troubleshooting the active code p16a7. I Inspected and done all of the requirements in the bullitins relevant to my 5.3 cover codes I have, which may have been caused by bad crimp at H6 terminal of X3 connector under the fuse box, and 3 know locations of ecm harness chafing points which I have all rulled out. I have done everything but replace the ecm and bring it to the dealer to check if I need an ecm firmware update. All I have left is a a powertrain warranty. What I have done in 10 hours of troubleshooting: load tested battery, checked charging system, checked all the fuses underhood, removed and took apart the fuse box to check for any terminal thats corroded, poorly crimped or unseated from its connector.All appeared perfect. tested kr35 relay, its coil circuit from the ecm when the falt actually occurs. When it wont start i rulled out the the fuse panel as the problem. I did all inspection and testing requirements in the attached technical service bulletins attached. I inspected only 6 inches of harness from the ecm for damage (non visible as it was properly secured to spec). With all 3 ecm connectors removed, inspected all male and female pins, did a pin draw test to see if there were any worn female terminals of the k20 3 ecm connectors. with ecm disconnected, while shaking squizing, bending 10 inches of ecm harness from the plugs, I was continuity testing each ignition, batt wire from the ecm plugs to the Ignition relay terminal 3 whicj was was relays output. All were 0.0hms. Since that is useless static test, I did a static voltage with no load then with a introduced load on each wire (ecm not connected). With key on, ignition in service mode with a charger on the battery, with the 3 K20 ecm connectors disconnected. I did a static voltage test at the ecm plug, first compared the B+ feed to the ecm plug to each ignition feed wires to each of the 3 ecm connectors. No voltage difference. Then I did the same test again, but this time I put a 8 amp load on each wire (to rule out corroded wires). I compared the loaded voltage drop of the B+ ecm feed to the loaded voltage drop of each IGN wires feeding the ecm. All had an identical voltage drop under load. For that 8amp loaded test, I used one of the 2 ecm grounds one at a time, those ground fed to ecm are from I think it was G114. All of this voltage testing is done when the problem was not present because its in a warm garage.At this point I was no longer going to remove the airbox to futher inspect the ecm harness behind the left front strut mount. l Replaced the ignition ecm relay kr35 (k77) and the starter relay with gm parts. I brake cleaned and blew dry the ecm and its connector pins and closely inspected each pin a second time. The next thing I was going to do was install back probes in the ecm connectors to monitor the ign and b+ voltage at ecm connectors while the fault actually occurs. I need you to tell me which IGN wire to monitor as there are many going to the 3 ecm connectors. I dont exactly know which ignition wires the ecm is comparing to its battery feed voltage to cause the DTC I get. So after doing all this. I turned off the ignition and immediately torqued the left front tire. Which may have triggered this new set of codes according to this bullitin (#PIT5735B). The bellitin says if the the tires slightly rotate shortly after igntion is turned off it could generate these codes I got, which I never had ever before. A body control module software update may correct it but I think a latest update for the bcm and ecm my not be relevant to fix any of my problems. I currently do not have a CEL on, but 2 of my code scanners see these codes, which I cannot clear any of them manually, before during and after a 6 hour drive.So I did disturb the ecm harness the night before, The New active codes are p2535, p25a2,U0100. Pending codes are p0685, p0700.I will be back home in 5 days to continue troubleshooting but till then I need a new plan to troubleshoot these new codes. The new plan may include a full jerry can of fuel. Jk I will be disconnecting my lightbar completly to reference bulletin #PIT5743 which states aftermarket mods tied into the ignition circuit of the fuse box or IP causes a crank no start condition. I tied my light bar relay coil 85 power feed from ignition source in the instrument panel RAP ign source I think it was. I doubt this is the issue, if it was it would cause me crank nonstart issues year round and not just when its -20c or colder.