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Fitment notes: Heavy-duty diesel application requires high CCA rating; dual battery system available on some configurations
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Every control module on the 2020-2026 GMC Sierra 3500HD — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
📍 6L80/6L90: integrated with valve body inside transmission (TEHCM). Allison 1000: external on driver side of transmission case near pan rail. 10L80/10L90 (2020+): integrated with valve body inside tran
🔧 GM SPS2 via MDI2 with SGW unlock
⚠️ 10-speed transmission introduced 2020 on some gas models. All integrated TCMs require transmission pan removal. SGW unlock and VIN programming mandatory.
Electric Power Steering Control Module (EPSCM)2.5 hr R&Rsecurity gateway +0.5 hr▸ programming details
📍 Integrated with electric power steering gear assembly on frame, driver side below cab
🔧 GM SPS2 via MDI2 with SGW unlock
⚠️ Module integrated with steering gear; requires steering gear removal. Steering angle sensor calibration and SGW unlock required.
⚠️ Security gateway unlock code required from GM. VIN programming and theft deterrent relearn mandatory. 2024+ may have updated ECM hardware for emissions.
📍 Behind center stack touchscreen display in instrument panel
🔧 GM SPS2 via MDI2 with SGW unlock
⚠️ 8-inch standard, 13.4-inch available 2024+. VIN, SGW unlock, and feature configuration required. OnStar and navigation settings must be reconfigured. Wireless CarPlay/Android Auto on 2021+.
📍 Behind instrument panel, left of steering column, above fuse block
🔧 GM SPS2 via MDI2 with SGW unlock
⚠️ Routes communication between CAN buses. Implements security gateway requiring unlock code for programming other modules. Critical security module.
Auxiliary Heater Control Module (AHCM)1.0 hr R&Rdealer / factory tool +0.3 hrDiesel models with auxiliary cab heater▸ programming details
📍 Engine compartment, passenger side firewall area
🔧 GM SPS2 via MDI2
⚠️ Controls diesel-fired auxiliary heater for cold weather operation. Configuration required after replacement.
Magnetic Ride Control Module (MRCM)1.0 hr R&Rdealer / factory tool +0.4 hrDenali and High Country trims with Magnetic Ride Control▸ programming details
📍 Frame mounted, rear of vehicle near rear axle
🔧 GM SPS2 via MDI2
⚠️ Controls adaptive magnetic dampers. Calibration and ride height sensor relearn required. May require SGW unlock.
📍 Instrument panel, behind gauge cluster lens, accessible after steering column trim and cluster bezel removal
🔧 GM SPS2 via MDI2 with SGW unlock
⚠️ Mileage programming from BCM required. SGW unlock and configuration for installed options mandatory. 2022+ may have updated digital cluster on higher trims.
📍 Behind glove box, upper right side of instrument panel
🔧 GM SPS2 via MDI2 with SGW unlock
⚠️ OnStar subscription reactivation required. VIN, SGW unlock, and cellular provisioning mandatory. 5G capable module on 2023+ models.
Fuel Pump Control Module (FPCM)0.6 hr R&Rrelearn only +0.2 hr▸ programming details
📍 Frame mounted, driver side below cab, near fuel tank
🔧 Scan tool auto-relearn
⚠️ Controls fuel pump speed based on ECM commands. Auto-relearn typically sufficient; no VIN programming or SGW unlock required.
Seat Control Module (SCM)0.6 hr R&Rrelearn only +0.1 hrwith power seats (standard on most trims)▸ programming details
📍 Under driver and passenger front seats, mounted to seat frame
🔧 Scan tool auto-relearn
⚠️ One per power seat. Memory seat positions lost; customer must reprogram preferences. Heated/ventilated seat functions controlled by this module.
Headlamp Control Module (HCM)0.5 hr R&Raftermarket tool +0.2 hrwith automatic headlamps or LED/HID headlamps▸ programming details
📍 Behind left headlamp assembly in engine compartment
🔧 Autel MaxiSys or GM SPS2
⚠️ Controls headlamp leveling and automatic on/off. Basic configuration possible with high-end aftermarket tools.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2025 GMC Sierra 3500HD 6.6L V8 Duramax Diesel and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.