Oh no. We’ve all been there. The check engine light (CEL) on your dash illuminates, and your Harley-Davidson isn’t running right. Or, what might be even more confusing, the light comes on but the bike seems completely fine. What should you do, what does it mean? Is this cause for a tow? Can the bike operate normally until you can get it into a shop?

These questions are very common when a Harley-Davidson check engine light stays on. Keep reading below for information about how to determine which trouble code is associated with the CEL.

What Does a Check Engine Light Mean?

An illuminated check engine light is an indication that the motorcycle’s onboard diagnostic system detects a current or historic trouble code, known as diagnostic trouble codes (DTC).

Once exclusive to the automotive industry, motorcycle manufacturers like Harley-Davidson rely on onboard diagnostics to assist owners and technicians when a fault occurs.

Prior to electronic fuel injection (EFI), motorcycles had few, if any, sensors or complicated electronic equipment. Over the years, manufacturers like Harley-Davidson transitioned to fuel injection for a variety of reasons, including reliability, simplicity, fuel economy/emissions, and performance.

While this transition to EFI gave riders a simpler and more enjoyable ownership experience, it also made diagnostic work more challenging. Following the trend of automotive manufacturers, motorcycle manufacturers like Harley-Davidson adopted the standardized SAE convention for identifying and labeling onboard faults.

If the vehicle’s electronic control module detects an error within the system, it “throws a code,” causing the check engine light to illuminate. A DTC is directional information for an owner or technician to begin diagnostic work. The presence of a code doesn’t mean you should start replacing parts. A Harley-Davidson dealership service department or other qualified technician is your best bet if you are not comfortable or experienced with diagnosing electrical issues.

Harley trouble codes categories: (categories may vary based on model year and options)

  • Engine Control Module (ECM)
  • Body Control Module (BCM)
  • Speedometer (SPDO)
  • Radio (RAD)
  • Anti-Lock Braking System (ABS)
  • Turn Signal Security Module (TSSM)

All fuel-injected motorcycles have the ability to communicate trouble codes. However, some bikes require an external diagnostic tool. Luckily, H motorcycles have the ability to display Harley error codes right on the dash, no tool required!

To enter the diagnostic system and retrieve a trouble code, hold down the trip reset button while turning the ignition from off to on. This will allow you to cycle through the categories, and see which one indicates a code.

Harley Davidson Code List Categories

Trouble codes fall into one of three categories:

  • Current
  • Historic
  • Pending

Current codes display when the system detects an active fault. Simply clearing the code won’t resolve the issue, as the code will return once enough drive cycles occur in which the system recognizes the fault again.

Historic codes remain saved until they are intentionally cleared or roughly 40 ignition cycles (on/off) without recurrence. Historic codes assist with intermittent issues or faults.

Pending codes record when the system detects a fault but the fault has not occurred during enough drive cycles to set at current. If the fault resolves itself, the code will become a historic code, skipping current status.

How to Display Trouble Codes

Using the trip reset button, a Harley-Davidson owner can cycle through codes in each of the code categories and note the DTC itself. Listed below are possible codes and their meanings. Please note that not all codes will apply to every model based on year and options.

How to access codes without a diagnostic tool:

  1. Start with a known good battery and secure battery terminals
  2. Set run/stop switch to run position
  3. Hold down the trip reset button while turning the ignition to on position
  4. Click the trip button to cycle through modules and hold down trip button to display codes (displayed text will vary based on year and model)

Newer bikes display abbreviations to represent each module:

  • ECM: Electronic Control Module
  • BCM: Body Control Module
  • SPDO: Speedometer
  • RAD: Radio

Older bikes display letters to represent each module:

  • P: ECM
  • SP: Speedometer
  • T: Tachometer
  • B: ABS module

The onboard diagnostic system will also display a part number that corresponds to the trouble code, and it will allow you to clear the code. This part can be a bit tricky, since the part associated with the displayed number isn’t automatically bad. Also, it’s possible to see multiple codes related to one issue.

A motorcycle student makes an adjustment to a Harley-Davidson bike in an MMI lab.

Harley-Davidson uses abbreviations in their service manual, owner’s manual and for diagnostic work with trouble codes. We’ve listed common abbreviations and their meanings below:

  • ABS: Anti-Lock Braking System
  • ACR: Automatic Compression Release
  • AFR: Air Fuel Ratio
  • AIS: Active Intake Solenoid
  • ATS: Air Temperature Sensor
  • BAS: Bank Angle Sensor
  • BCM: Body Control Module
  • CAN: Controller Area Network
  • CCM: Cruise Control Module
  • CKP: Crank Position Sensor
  • DLC: Datalink Connector
  • DTC: Diagnostic Trouble Codes
  • ECM: Electronic Control Module
  • ECT: Engine Coolant Temperature
  • ECU: Electronic Control Unit
  • EFI: Electronic Fuel Injection
  • EFP: Electronic Fuel Pump
  • ET: Engine Temperature sensor
  • FI: Fuel Injectors
  • FPR: Fuel Pressure Regulator
  • H-DSSS: Harley-Davidson® Smart Security System
  • HCU: Hydraulic Control Unit, ABS
  • HFSM: Hands Free Security Module
  • HO2S: Heated Oxygen Sensor
  • IAC: Idle Air Control actuator
  • IAT: Intake Air Temperature sensor
  • ICM: Ignition Control Module
  • IMAP: MAP + IAT in one unit
  • ISS: Ion Sensing System
  • JSS: Jiffy Stand Sensor
  • LHCM: Left Hand Control Module
  • MAP: Manifold Absolute Pressure sensor
  • MHR: Right Hand Control Module
  • RCM: Reverse Control Module
  • TCA: Throttle Control Actuator
  • TGS: Twist Grip Sensor
  • TMAP: Intake Air Temperature / Manifold Absolute Pressure equipment
  • TPS: Throttle Position Sensor
  • TSM / TSSM: (Turn Signal / Turn Signal Security Module)
  • VE: Volume Efficiency
  • VIN: Vehicle Identification Number
  • VSS: Vehicle Speed Sensor
  • WSS: Wheel Speed Sensor

These abbreviations, and the accompanying list of trouble codes, can be a great start when your Harley-Davidson check engine light comes on. As mentioned above, if you are not comfortable with electrical diagnostic work, a dealership or qualified technician can offer assistance. Please keep in mind that even though you have the ability to clear a DTC using the onboard diagnostic feature, you shouldn’t clear the code prior to your service appointment. Let the technician view and clear the codes as they troubleshoot the issue.

Expandable Lists of Trouble Codes by Category

  • ABS Codes (C)

  • COM Codes (U)

  • ECM Codes (P)

  • RAD Codes (B)

How Does This Apply to a Career in the Field?

Some Harley-Davidson owners perform their own service and repair, but most draw the line at electrical diagnostic work. Technicians who can quickly diagnose and repair electronic system faults are always in demand. Simply observing and identifying a code isn’t enough to fix a motorcycle with an illuminated check engine light, nor is swapping out parts without a thorough understanding of the root cause of the failure. Like anything else, experience and practice will allow for an entry-level technician to become a full diagnostic tech.

Train for the Motorcycle Industry at MMI

In Motorcycle Mechanic Institute’s 48-week Motorcycle Technician Training Program,7 students can learn the foundations of motorcycle, ATV, side-by-side and personal watercraft to prepare for a career as a motorcycle technician.1.1 To learn more, visit our program page and request information to talk with an Admissions Representative today.

MMI Campuses That Offer Motorcycle Mechanic Training

With classes starting every 3-6 weeks, no need to wait to start your career.
Hands-on training.Get hands on experience with the industry's leading brands.
No Pressure to commit.Get answers to your questions without any obligations.
Or Call Now 800.834.7308

1.1 ) MMI is an educational institution and cannot guarantee employment or salary.
2 ) For program outcome information and other disclosures, visit www.uti.edu/disclosures.
7 ) Some programs may require longer than one year to complete.

Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.


Take 60 seconds and find out how you can get trained.

Step 1 of 1

By submitting this form, I agree that MIAT College of Technology, Universal Technical Institute, Inc., Custom Training Group, Inc. and their representatives may email, call, and / or text me with marketing messages about educational programs and services, as well as for school-related communications, at any phone number I provide, including a wireless number, using prerecorded calls or automated technology. I understand that my consent is not required to apply, enroll or make any purchase. I further understand and agree that I may instead call MIAT at 1-800-477-1310 for Canton, MI and 1-888-547-7047 for Houston, TX or UTI at 1-800-913-7524 to request admission information. I understand that if I do submit this form, I may unsubscribe within marketing emails or opt-out of text messages at any time by replying “STOP.” Standard text message and data rates may apply.By submitting this form, I further understand and agree that all information provided is subject to UTI’s Privacy Policy available at www.uti.edu/privacy-policy and UTI's SMS Terms and Conditions available at www.uti.edu/sms-terms-conditions.