Quick Answer: A 2020–2023 L5P Duramax commonly uses three CAN Bus plugs: two smaller NOx-related connections and one larger DEF connection. One plug is in the engine bay, while the other two are positioned along the underbody and frame harness.
Plan about 30–75 minutes. The revised layout uses fewer plugs than a 2017–2019 truck, but the underbody connectors can still be difficult to identify when they are covered by road dirt or previous wiring work.
Installation Overview
| Detail | 2020–2023 L5P |
|---|---|
| Typical total plugs | 3 |
| NOx connections | 2 smaller plugs |
| DEF connection | 1 large plug |
| Difficulty | 3 out of 5 |
| Estimated time | 30–75 minutes |
| Work areas | Engine bay and underbody |
This guide is only for the revised 2020–2023 layout. Owners of earlier trucks should use the 2017–2019 L5P four-plug installation guide.
Before You Start
- Confirm the truck is a 2020, 2021, 2022, or 2023 L5P Duramax.
- Confirm the selected kit is the 2020–2023 configuration.
- Compare the two smaller plugs with the larger DEF plug.
- Park on level ground and chock the wheels.
- Allow the exhaust to cool completely.
- Disconnect the negative terminals from both batteries.
- Photograph the factory connections before opening them.
Select the correct model-year option when ordering the 2020–2023 L5P CAN Bus Plug Kit.
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Tools and Supplies
- Wheel chocks
- Safety glasses and mechanic gloves
- Work light or headlamp
- Small plastic pick
- Trim-clip removal tool
- Electrical contact cleaner
- Clean shop towels
- Harness clips or zip ties
- Compatible scan tool
- Properly rated jack stands if more clearance is required
2020–2023 L5P CAN Bus Plug Location Map
| Plug | Connection type | Typical area |
|---|---|---|
| Plug 1 | NOx connection | Rear or upper engine-bay wiring near the firewall |
| Plug 2 | Underbody NOx connection | Frame-mounted underbody harness |
| Plug 3 | Large DEF connection | Underbody DEF-related harness |
Plug 1 Location: Engine Bay
Look near the rear and upper area of the engine bay close to the firewall, intake tube, and upper wiring harness.
Use the picture to find the correct area, then verify the connector body, locating keys, and terminal arrangement. Do not force an earlier-model plug into this connection.
Plug 2 Location: Underbody NOx Connection
Move underneath the truck and follow the related NOx sensor wire toward its electronic module and vehicle-side harness connection.
Cab length, bed length, and previous exhaust work can change the visual reference points. Following the sensor wire is more reliable than measuring from a wheel or crossmember.
Plug 3 Location: Large DEF Connection
The third connection is the larger DEF-related plug. Identify it by its larger connector body, terminal arrangement, locating keys, and locking mechanism.
A correctly matched plug should connect with firm hand pressure. If it requires heavy force, stop and recheck the selected kit and connector location.
How to Identify the NOx Sensor and Module
The metal NOx sensor threads into the exhaust. Its cable leads to the black electronic module and then to the vehicle-side harness connection.
How to Install the Three CAN Bus Plugs
Step 1: Disconnect both batteries
Turn the ignition off, remove the key, and disconnect both negative battery terminals. Wait several minutes for the control modules to power down.
Step 2: Separate the plugs by size
Lay out the two smaller NOx plugs and the larger DEF plug. Compare their body shapes and locating keys before working under the truck.
Step 3: Locate all three connections
Find the engine-bay connection first, then trace the underbody sensor wiring to the remaining two vehicle-side connections.
Step 4: Photograph and label them
Take a picture before disconnecting each module. Label the connections as Plug 1, Plug 2, and Plug 3.
Step 5: Clean the connector housings
Remove road dirt before releasing a lock. Use electrical contact cleaner when required and let the connector dry.
Step 6: Release the secondary lock
Move the secondary lock before pressing the main release tab. Pull on the connector housing rather than the wires.
Step 7: Inspect the terminals
Check for bent pins, corrosion, moisture, pushed-back terminals, torn seals, or cracked housings.
Step 8: Install the matched plug
Align the locating keys and push the plug straight into the vehicle-side connector. Close the secondary lock and perform a light pull test.
Step 9: Secure the wiring
Keep the harness away from the exhaust, driveshaft, suspension travel, sharp frame edges, and areas where water can collect.
Step 10: Reconnect and verify
Reconnect both batteries, follow the required startup or calibration sequence, and scan all available modules for diagnostic codes. If the build uses OBDII-based tuning, confirm the 2017–2023 L5P OBDII flash tuning interface matches the selected hardware path before final verification.
Post-Installation Checklist
- Three plugs accounted for
- Two smaller NOx connections correctly matched
- Large DEF connection correctly matched
- All primary and secondary locks closed
- No bent or pushed-back terminals
- Harness secured away from heat and movement
- Both batteries charged and connected
- No new U-codes or warning messages
Explore 2020–2023 L5P Duramax Upgrades
Working on a 2020–2023 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.
Troubleshooting 2020–2023 Installation Problems
The kit contains the wrong number of plugs
Confirm that the 2020–2023 configuration was selected. Do not use the four-plug count from an earlier-model guide.
The engine-bay plug will not fit
Verify the connector shape and locating keys. The revised engine-bay harness differs from the 2017–2019 layout.
The large connector will not lock
Clean dirt from the secondary lock and inspect it for damage. Confirm that the large DEF plug is being used at the correct connection.
The truck shows several U-codes
Check battery voltage and both battery connections first. Then inspect each recently handled connector for an incomplete lock, bent terminal, incorrect plug, or a mismatched L5P tuning path.
Codes appear after wet weather
Inspect the underbody seals and mounting positions for water intrusion. Do not leave the connections hanging where water can collect.
If the three-plug install is one part of a larger off-road or competition-use setup, verify the plug count, exhaust layout, downpipe choice, EGR hardware, and tuning support as one system before final verification. For owners comparing a bundled path, an EGR, DPF, downpipe and CAN Bus plug L5P all-in-one kit may be easier to match than buying each major component separately.
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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: 2020–2023 L5P CAN Bus Plug Installation
Q: How many CAN Bus plugs does a 2020–2023 L5P use?
A: The revised layout commonly uses three plugs: two smaller NOx connections and one larger DEF connection.
Q: Does a 2020 L5P use the same plugs as a 2019?
A: No. The model-year groups use different layouts and may use different connector configurations.
Q: Where is the first connection?
A: Plug 1 is in the upper engine-bay wiring area near the firewall and intake tube.
Q: How do I find the underbody NOx connection?
A: Start at the exhaust-mounted NOx sensor and follow its cable toward the electronic module and vehicle-side harness.
Q: Which plug is the DEF connection?
A: The DEF-related connection uses the larger plug in the 2020–2023 set.
Q: How long does installation take?
A: Plan approximately 30–75 minutes. Dirt, corrosion, damaged locks, and limited access can extend the job.
Q: Can the plugs replace tuning?
A: No. CAN Bus plugs do not unlock or recalibrate the ECM.
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
Lars
Diesel Performance Engineer | 15+ Years Experience
"Empower Your Beast: Run Cooler, Pull Harder, Last Longer."
