Derringer for 2020 GM L5P

Banks Derringer® Diesel Tuner
Installation and Owners Manual

2020 GM 2500 L5P 6.6L Duramax
EO #: D-161-136

Part #s 66582, 66592, 66792, 66682, 66692 & 66793

Please read through the following instructions thoroughly before starting your installation. If you have any questions please visit our Support Page.

Tools required:
  • Zip-ties (6” or longer) 
  • Cutting tool (i.e. Diagonal Cutters) 
  • Standard flat-blade screwdriver 
  • Push-rivet removal tool
  • 10mm socket
  • Socket wrench
  • Electrical tape (optional)
  • Metal coat hanger (optional)

General Installation Practices

1. Before starting work, familiarize yourself with the installation procedure by reading all of the instructions.

2. The exploded views provide only general guidance. Refer to each step and section diagram in this manual for proper instruction.

3. Throughout this manual, the left side of the vehicle refers to the driver’s side and the right side to the passenger’s side. 

4. Disconnect the negative (ground) cable from the battery (or batteries, if there are more than one) before beginning work. The OEM battery clamp can be removed using a 10mm socket or wrench. 

5. Route and tie wires and hoses a minimum of 6″ away from exhaust heat, moving parts, and sharp edges. Clearance of 8″ or more is recommended where possible. 


THIS IS A HIGH PERFORMANCE  PRODUCT. USE AT YOUR OWN RISK. Do not use this product until you have carefully read the following agreement. 

This sets forth the terms and conditions for the use of this product. The installation of this product indicates that the BUYER has read and understands this agreement and accepts its terms and conditions.

Disclaimer of Liability

Gale Banks Engineering Inc. and its distributors, employees, and dealers(hereafter “SELLER”) shall in no way be responsible for the product’s proper use and service. The BUYER hereby waives all liability claims.

The BUYER acknowledges that he/she is not relying on the SELLER’s skill or judgment to select or furnish goods suitable for any particular purpose and that there are no liabilities which extended beyond the description on the face hereof and the BUYER hereby waives all remedies or liabilities, expressed or implied, arising by law or otherwise, (including without any obligations of the SELLER with respect to fitness, merchantability, and consequential damages) whether or not occasioned by the SELLER’s negligence. The BUYER is responsible to fully understand the capability and limitations of his/her vehicle according to manufacturer specifications and agrees to hold the SELLER harmless from any damage resulting from the failure to adhere to such specifications.

The SELLER disclaims any warranty and expressly disclaims any liability for personal injury or damages. The BUYER acknowledges and agrees that  the disclaimer of any liability for personal  injury is a material term for this agreement  and the BUYER agrees to indemnify  the SELLER and to hold the SELLER harmless from any claim related to the item of the equipment purchased. Under no circumstances will the SELLER be liable for any damages or expenses by reason of the use or sale of any such equipment.

The BUYER is responsible to obey all applicable federal, state, and local laws, statutes, and ordinances when operating his/her vehicle, and the BUYER agrees to hold SELLER harmless from any violation thereof.

The SELLER assumes no liability regarding the improper installation or misapplication of its products. It is the installer’s responsibility to check for proper installation and if in doubt, contact the manufacturer.

The BUYER is solely responsible for all warranty issues from the automotive manufacturer.

Limitation of Warranty

Gale Banks Engineering Inc. (hereafter “SELLER”), gives Limited Warranty as to description, quality, merchantability, fitness for any particular purpose, productiveness, or any other matter of SELLER’s product sold herewith. The SELLER shall be in no way responsible for the product’s open use and service and the BUYER hereby waives all rights except those expressly written herein. This Warranty shall not be extended or varied except by written instrument signed by SELLER and BUYER

Please see enclosed warranty information card, or go to for warranty information regarding your product. All products that are in question of Warranty must be returned shipping prepaid to the SELLER and must be accompanied by a dated proof of purchase receipt. All Warranty claims are subject to approval by Gale Banks Engineering Inc.

Under no circumstance shall the SELLER be liable for any labor charged or travel time incurred in diagnosis for defects,removal, or reinstallation of this product,or any other contingent expense.

Under no circumstances will the SELLER be liable for any damage or expenses incurred by reason of the use or sale of any such equipment.


The BUYER may promptly return this product, in a new and unused condition, with a dated proof-of-purchase, to the place-of-purchase within thirty (30) days from date-of-purchase for a full refund, less shipping and/or restocking fee.

The installation of this product indicates that the BUYER has read and understands this agreement and accepts its terms and conditions.

1.0 Installation of Wire Harness and Derringer Tuner

1.1 Derringer Tuner System Configuration

97702 Derringer 2020 GM L5P

1.2 Derringer Sensor Harness Installation


Ensure that the engine bay is cool

Remove keys from the ignition. Disconnect the battery GROUND (-) cables. Secure the cables so that they do not come in contact with the battery posts during the installation.

NOTE: If the ECU is powered on when the sensors are disconnected, your vehicle will show diagnostic trouble codes. These codes can be cleared later using the iDash.

97702 Derringer 2020 GM L5P

Sensor Location/Connection Instructions

1. GM L5P Derringer harness connects to FRP and TMAP sensors.
When disconnecting the plugs, pull only on the connector, do not pull on the wires. (No tools required) 

97702 Derringer 2020 GM L5P

2. Locate the TMAP and FRP connectors on the GM L5P engine bay.

3. On the top of the L5P engine, you will find a Temp/Manifold Absolute Pressure (TMAP) sensor mounted on the intake manifold. Disconnect the TMAP sensor plug (4 Pin) by sliding the back the grey locking tab on the OEM harness connector. After sliding back the locking tab, pull the plug from the TMAP sensor. If the connector doesn’t easily pull away from the sensor, use your thumb to slightly depress the grey locking tab. Jiggling the connector gently should allow it to slide off the sensor.

There are two similar-looking OEM connectors next to the previously mentioned TMAP sensor. The following FRP connection that will be utilized is the 8 pin connector CLOSEST to the TMAP sensor.

4. To disconnect the OEM harness from the FRP connection, slide back the OEM harness connector’s red locking tab. Use your thumb to depress the black plastic tab just in front of red tab. This will release the connector and you can pull it away from the OEM FRP connection.

5. Plug the Derringer harness connectors labeled MAP between the MAP sensor and MAP OEM harness. Next, plug the Derringer harness connectors labeled FRP between the FRP connection and the FRP OEM harness.

6. It is suggested to route the rest of the Derringer harness along the OEM harness route. Connect the Derringer module to the Derringer sensor harness. Locate a place to secure the Derringer module near or along the fender, then zip-tie it in place.

 The pictured mounting location of the Derringer Tuner is optional. It is best to mount close to the firewall and route the harness along the OEM harness.

1.3 Derringer Tuner Installation

1. Connect the Derringer Module to the Derringer Sensor Harness and the Starter Cable.

2. Rotate the locking ring towards so all marks line up at the 12 o’clock position then connect the mating ends together ensuring proper alignment using the 12 o’clock marks. Pushing the pieces together without proper alignment could result in bent pins.

97702 Derringer 2020 GM L5P

3. Rotate the locking ring clockwise towards the lock icon until you feel a click.

97702 Derringer 2020 GM L5P

4. Locate a place to secure the Derringer module near or along the fender, then zip-tie it in place. Ensure the LED indicator is viewable. If there is extra cable length, secure it out of the way with zip-ties.

NOTE: The pictured mounting location of the Derringer Tuner is optional. It is best to mount close to the firewall and route the harness along the OEM harness.

97702 Derringer 2020 GM L5P

5. Check all connectors for proper installation, then connect the battery terminal(s).

1.4 Starter Cable Firewall Installation

Starter Cable Sidewall Access

1. Route the starter cable behind the driver-side reservoir under the foam divider through the fender and retrieve it while the driver side door is open.

97702 Derringer 2020 GM L5P

2. Locate the grommet on the sidewall under the cable harness which passes through the sidewall on the drivers side door jam.

97702 Derringer 2020 GM L5P

3. Remove the grommet with a plastic pry tool. A flat-blade screwdriver can also be used, however, it’s recommended to put electrical tape over the tip to avoid scratching the paint.

4. Cut a 1/4” hole through the gromet and feed the starter cable through it.

97702 Derringer 2020 GM L5P

5. Run the starter cable through the door jam and out from the footwell and pull it out.

97702 Derringer 2020 GM L5P

1.5 In-Cab Installation

1. Plug the OBD-II Cable into the OBD-II port located under the dash.

97702 Derringer 2020 GM L5P

2. Remove the side dash cover using a plastic pry tool or screwdriver. Route the Starter Cable and OBD-II Cable to the iDash. 

97702 Derringer 2020 GM L5P

3. Use this area to store any excess wire.

97702 Derringer 2020 GM L5P

iDash Configuration

1. Connect the Starter Cable to the iDash 6-Pin Port.

97702 Derringer 2020 GM L5P

2. Check for the pre-installed Jumper Block to the iDash 2-Pin termination jumper. If this is your only iDash, leave the jumper in place. However, if you’re adding multiple iDashes, only the last iDash in the chain should have a jumper. This jumper tells the Banks Bus network where to find the end of the circuit.

3. If adding multiple iDash units, connect the Y-Cable to the 6-pin port of the first and second iDash.

A. Connect the Starter Cable to the Y-Cable as shown.

97702 Derringer 2020 GM L5P

4. Install the iDash 1.8 in an A-pillar mount or a suction cup windshield-mount gauge-pod.

1.6 Checking Derringer Tuner Connection

1. While the engine is running, check the LED indicator on the Derringer. 

A. Under proper operation the LED will steadily blink green.

B. If the LED is always off or blinking red, refer to “Section 3:  Troubleshooting

97702 Derringer 2020 GM L5P

2. On the iDash, navigate to the Gauge Layout, scroll down, then select the “Derringer” layout. Using the UP and DOWN arrow buttons to adjust the power level settings.

97702 Derringer 2020 GM L5P

If the power level cannot be adjusted, refer to “Section 3: Troubleshooting

97702 Derringer 2020 GM L5P

2.0 Derringer Tuner Operation

Setting Desired Power Level:

The Derringer is equipped with multiple power levels. You can set the desired power level while driving, however, it is recommended that you do not switch the power level under high load applications.

iDash 1.8 configuration: 

When the Derringer is connected to an iDash, there are a total of 6 power levels (level 6, 5, 4, 3, 2, and stock). The power level can be changed by pressing the UP and DOWN buttons at any time. If you have the Derringer layout loaded, you will see the power level change at the bottom left corner. If you have any other layout loaded, a message box will pop up to notify you of the power level change.

97702 Derringer 2020 GM L5P


This mode is to be used when peak engine performance is desired. This mode has been optimized for maximum power output along with improved turbo response by tuning fuel delivery and boost. 


The plus calibration is designed for use in everyday driving. This power level adds a noticeable punch under high load acceleration by improving turbo response and power. Power in this mode can be sustained for a prolonged duration. 


Stock mode turns OFF your Derringer tuner. Throttle response and power return to stock levels.

Banks ActiveSafety®

Anytime aftermarket electronics are introduced to your vehicle, it is important to know that they are not going to cause damage. Banks builds in a suite of ActiveSafety features to safeguard your vehicle:

» Software that monitors and diagnoses itself to ensure proper function.

» Self-monitoring hardware that provides automatic bypass should something malfunction.

The Derringer Tuner module monitors multiple parameters and adjusts its output controls to protect the driveline. The Derringer Tuner monitors engine coolant temperature (ECT) and will limit the additional power that it provides anytime the ECT is outside of optimal operating range to protect the engine.

Power Added (%):

When connected to an iDash while displaying the “Derringer” layout, the vertical bar graph on the right-hand side represents, in real-time, how much power the Derringer is adding. In Stock Mode there will be no change to the bar graph and in Sport Mode/Level 6 the bar graph will reach 100% under proper operating conditions. Percent power added is affected by safety features such as Engine Coolant Temperature, Exhaust Gas Temperature, Regen., and various transmission parameters, so it might not always fully reach 100%. The “Power Added” data can also be displayed on ANY layout as a numeric value by selecting it from the “Derringer” category of parameters.

97702 Derringer 2020 GM L5P

Automatic Transmission  Learning:

6.6L GM Duramax pickup trucks equipped with the Allison 1000 6-speed automatic transmission use an adaptive shift control logic. After the initial installation of the Derringer Tuner, wide-open throttle shifts may feel soft when switching to higher power levels. Also, when switching to lower power levels, shifting may feel harsher. Continued use at a single power level will provide more consistent shifting performance.

To accelerate the learning process perform the following sequence at a location where it is safe to accelerate without exceeding the posted speed limit.

1. Set the Derringer Tuner to Stock Mode power setting, start the truck and allow the engine to reach normal operating temperature.

2. Adjust the Derringer Tuner to Plus Mode/Level 3 power setting.

3. Drive your vehicle for 5-10 miles, ensuring a complete shift cycle through each gear (The transmission shift learning process requires 15-30 complete shift cycles to learn a new shift program).

4. Increase power level to Sport Mode/Level 6 and repeat Step 3.

3.0 Troubleshooting  

97702 Derringer 2020 GM L5P

Normal Operation

Your Derringer Tuner has a built-in, self-diagnostic system. The status of the Derringer system is communicated via the LED on the module. When the Derringer Tuner is functioning properly the LED will flash green. 

Derringer Not Powered

When the LED is not illuminated, the Derringer Tuner is not powered on. If the ignition is on and the LED is not illuminated, check the TMAP connections on the vehicle and ensure they are fully engaged. 

No Communication with iDash

Check that your wiring matches the figure in Section 1.1 Wiring Diagram:  iDash 1.8” Configuration or for multiple iDash 1.8 Gauges. 

Common sources of Derringer communication errors (D-ERR) are wrong caps attached to the Derringer and/or the In-Cab Termination Cable is not installed. A Black Termination Cap must be connected to the Derringer and only one In-Cab Termination Cable should be attached to one of the iDash units.

LED Error Code 

When faults are detected, the Derringer Tuner will flash a diagnostic code. These diagnostic codes are comprised of 2 digits. Each digit is expressed by the flashing red LED. 

A code can be determined by counting the number of red flashes displayed before the LED flashes green for the first digit and the number of red flashes after the LED flashes green for the second digit. After the diagnostic code is displayed, additional codes will be displayed in sequence, separated by 4 seconds with the LED off. Once all codes are displayed the Derringer will begin sending the codes again. Once you have written down all diagnostic codes being displayed, consult the following tables for a description of the code along with the action to be taken.    

iDash Display Error Code

If error code “D-ERR!” appears on the iDash, refer to the following to display the code and description:

Settings > Diagnostics > Select the module that is giving the error

Derringer Tuner (GM L5P application)

Technical Support

If you require support, call or text (800) 601-8072 during normal business hours, Monday-Friday. We can also be reached via Facebook messenger.