Quick Answer: A 2017–2019 L5P Duramax commonly uses four CAN Bus plugs: three smaller NOx connections and one larger DEF connection. Plug 1 is in the engine bay, Plug 2 is inside the front passenger-side frame, Plug 3 is outside the frame near the front driver-side wheel, and Plug 4 is behind the rear passenger-side wheel.
Plan 45–90 minutes for the job. The connectors are easy to install once found, but road dirt, tight frame access, and similar-looking harness connections can slow down a first-time installer.
Installation Overview
| Detail | 2017–2019 L5P |
|---|---|
| Typical total plugs | 4 |
| NOx connections | 3 smaller plugs |
| DEF connection | 1 large plug |
| Difficulty | 3 out of 5 |
| Estimated time | 45–90 minutes |
| Work areas | Engine bay and underbody |
This is the earlier L5P plug layout. If your truck is a 2020–2023 model, use the 2020–2023 L5P CAN Bus plug installation guide instead.
Before You Start
- Confirm the truck is a 2017, 2018, or 2019 L5P Duramax.
- Confirm the kit contains three smaller plugs and one larger plug.
- Park on solid, level ground.
- Let the exhaust cool completely.
- Disconnect the negative terminals from both batteries.
- Photograph each connector before opening it.
- Never work under a truck supported only by a hydraulic jack.
The 2017–2019 L5P CAN Bus Plug Kit must be selected using the correct model-year option.
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Tools and Supplies
- Wheel chocks
- Safety glasses and mechanic gloves
- Work light or headlamp
- Small plastic pick
- Trim-clip tool
- Electrical contact cleaner
- Clean shop towels
- Factory-style harness clips or zip ties
- Scan tool capable of reading U-codes
- Properly rated jack stands if additional clearance is needed
2017–2019 L5P CAN Bus Plug Location Map
| Plug | Type | Location |
|---|---|---|
| Plug 1 | NOx connection | Upper rear corner of the engine bay |
| Plug 2 | Large DEF connection | Inside the frame near the front passenger-side wheel |
| Plug 3 | NOx connection | Outside the frame near the front driver-side wheel |
| Plug 4 | NOx connection | Inside the frame behind the rear passenger-side wheel |
Plug 1 Location: Engine Bay
Open the hood and stand in front of the truck. Look toward the upper rear corner of the engine compartment near the firewall, battery, and brake-fluid reservoir.
After finding the general area, move closer and identify the factory harness connection. Do not rely only on “left” or “right” wording because viewing direction can make those descriptions confusing.
Plug 2 Location: Large DEF Connection
Move underneath the front passenger side and look inside the frame near the front passenger-side wheel.
This is the largest plug in the four-plug set. Clean road dirt from the connector before trying to move the secondary lock or release tab.
Plug 3 Location: Outside the Front Frame
Plug 3 is outside the frame near the front driver-side wheel. Approach the connection from the outside edge of the frame instead of looking straight up from the center of the truck.
Do not choose the connector based only on position. Confirm the terminal count, body shape, locating keys, and locking-tab orientation.
Plug 4 Location: Rear Passenger-Side Frame
Plug 4 is inside the frame behind the rear passenger-side wheel. This is often the dirtiest connection because it is exposed to water, mud, and road salt.
Clean the connector before opening it. Avoid prying hard on the locking tab because a damaged lock can allow the plug to loosen later.
How to Install the Four CAN Bus Plugs
Step 1: Disconnect both batteries
Turn the ignition off, remove the key, and disconnect the negative terminals from both batteries. Wait several minutes for the control modules to power down.
Step 2: Lay out and identify the plugs
Separate the three smaller NOx plugs from the single large DEF plug. Do not assume that similar-looking connectors are interchangeable.
Step 3: Photograph the factory connections
Take a clear picture before disconnecting each module. Label the locations as Plug 1 through Plug 4 with masking tape.
Step 4: Clean each connection
Remove loose dirt before opening the connector. Use electrical contact cleaner when needed and allow the terminal area to dry.
Step 5: Release the secondary lock
Some connectors use a secondary lock that must be moved before the main release tab works. Pull on the plastic housing, not the wires.
Step 6: Inspect the terminals
Check for bent pins, green corrosion, water, torn seals, pushed-back terminals, cracked housings, or broken locking tabs.
Step 7: Install the matched plug
Align the locating keys and push the plug straight into the vehicle-side connector. You should feel or hear the lock engage.
Step 8: Perform a pull test
Close the secondary lock, then pull lightly on the connector housing. Do not pull on the wiring.
Step 9: Secure the harness
Keep the plug and wiring away from the exhaust, driveshaft, suspension movement, sharp frame edges, and areas where water collects.
Step 10: Reconnect both batteries
Reconnect both batteries and follow the required calibration or startup sequence for the truck’s configuration. If the build uses OBDII-based tuning, confirm the 2017–2023 L5P OBDII flash tuning interface matches the hardware path before scanning.
Step 11: Scan the truck
Read all available control modules. Record any diagnostic codes before clearing them.
Post-Installation Checklist
- Four plugs accounted for
- Large plug installed at the correct DEF connection
- Three smaller plugs installed at their correct locations
- All primary and secondary locks closed
- No terminals bent or pushed backward
- Harness secured away from heat and moving parts
- Both batteries connected and charged
- No new communication codes
If the CAN Bus plug install is part of a broader off-road or competition-use build, confirm that the exhaust hardware, EGR components, downpipe, plug configuration, and tuning path are matched before final startup. For owners who want those major parts planned together, an EGR, DPF, downpipe and CAN Bus plug L5P all-in-one kit can reduce the risk of mixing incompatible components.
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Troubleshooting 2017–2019 Installation Problems
One plug is left over
Recheck all four locations. The rear passenger-side frame connection is the easiest one to miss.
The large plug will not fit
Confirm that you are at the large DEF-related connection inside the front passenger-side frame. Do not modify the connector keys.
The truck shows multiple U-codes
Check both batteries first, then inspect the most recently handled connectors for incomplete locks, bent terminals, incorrect plug placement, or a mismatched L5P tuning path.
Codes return after rain
Inspect the frame-mounted connections for water intrusion, torn seals, or a mounting position that allows water to collect.
Explore 2017–2019 L5P Duramax Upgrades
Working on a 2017–2019 Chevy Silverado or GMC Sierra 6.6L L5P Duramax? Explore vehicle-specific CAN Bus plugs, tuning interfaces, delete hardware, CCV reroute kits, downpipes, and other upgrade options for lawful off-road or competition builds. Always check the model year, cab configuration, and product fitment before ordering.
Related Guides
- L5P CAN Bus Plug Purpose, Fitment and Model-Year Guide
- What Do You Need for an L5P Duramax Off-Road Build?
- Complete L5P Duramax Regen Guide
Legal and Use Notice
CAN Bus plugs used with emissions-system removal or bypass are intended only for off-road, closed-course, competition, export, or other legally permitted applications. Street-driven trucks should retain functioning factory emissions equipment.
FAQ: 2017–2019 L5P CAN Bus Plug Installation
Q: How many CAN Bus plugs does a 2017–2019 L5P use?
A: The earlier L5P layout commonly uses four plugs: three smaller NOx plugs and one large DEF plug.
Q: Where is Plug 1?
A: Plug 1 is in the upper rear corner of the engine bay near the firewall, battery, and brake-fluid reservoir area.
Q: Where is the large DEF plug?
A: The large Plug 2 connection is inside the frame near the front passenger-side wheel.
Q: Which plug is easiest to miss?
A: Plug 4 behind the rear passenger-side wheel is often missed because it is farther back and may be covered with road dirt.
Q: How long does installation take?
A: Plan approximately 45–90 minutes. Corrosion, mud, damaged locks, and limited underbody clearance can increase the time.
Q: Do I need a lift?
A: No, but additional clearance can make the frame connections easier to inspect. Use properly rated jack stands if the truck is raised.
Q: Can the plugs replace compatible calibration?
A: No. The plugs do not unlock or recalibrate the ECM.
Lars
Diesel Performance Engineer | 15+ Years Experience
"Empower Your Beast: Run Cooler, Pull Harder, Last Longer."
