Motorcycle Ignition Systems: What Are They and How Do They Work?
When it comes to working on motorcycles, there's a lot to know! Learn about motorcycle ignition systems, what CDI boxes are and why they're important.
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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 – including a handy Harley-Davidson code list!
Key Summary Points
- An illuminated CEL on a Harley-Davidson motorcycle indicates that the onboard diagnostic system has detected a current or historic trouble code, signaling a potential issue with the motorcycle’s systems.
- Harley-Davidson motorcycles use a standardized system of diagnostic trouble codes (DTCs) to help owners and technicians identify and diagnose faults within the motorcycle electronic control module and other systems such as the body control module (BCM), speedometer (SPDO) and anti-lock braking system (ABS).
- Owners can access these trouble codes without the need for an external diagnostic tool by holding down the trip reset button while turning the ignition from off to on, allowing them to cycle through the categories and note the DTCs displayed on the dash.
- Trouble codes are categorized into current, historic and pending, with current codes indicating active faults, historic codes saved until cleared or after roughly 40 ignition cycles without recurrence, and pending codes indicating faults that have not occurred frequently enough to be set as ‘current’.
- For those not comfortable with electrical diagnostic work, it is recommended to seek assistance from a Harley-Davidson dealership service department or a qualified technician, as interpreting and addressing these codes requires specific knowledge and experience.
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What Does a Check Engine Light Mean?
An illuminated check engine light indicates that the motorcycle’s onboard diagnostic system detects a current or historic trouble code, known as a diagnostic trouble code (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 code categories (categories may vary based on model year and options) include:
- 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, Harley motorcycles have the ability to display error codes right on the dash – no tools 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.
Read: What Is a Motorcycle Transmission & How Does It Work?
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:
- Start with a known good battery and secure battery terminals
- Set run/stop switch to run position
- Hold down the trip reset button while turning the ignition to on position
- 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
- S: TSM/TSSM
- 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.
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.
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How to check codes on a Harley
To check codes on a Harley-Davidson motorcycle, you will need to use the diagnostic port located under the seat or near the ignition. Here’s a step-by-step guide:
- Gather your tools: You will need a compatible diagnostic scanner or a code reader specific to Harley-Davidson models to access the onboard diagnostics.
- Locate the diagnostic port: Remove the seat or any covers necessary to access the diagnostic connector. This is typically a 2-pin or 6-pin connector.
- Connect the scanner: Plug the diagnostic scanner into the port. Ensure that your motorcycle is turned on, but the engine doesn't need to be running.
- Retrieve codes: Follow the instructions provided with your scanner to retrieve any error codes. The scanner will communicate with the motorcycle's onboard computer and display any existing codes that indicate issues.
- Interpreting codes: Reference the Harley-Davidson service manual or the code table provided with your scanner to understand what the codes mean. Each code corresponds to specific faults or issues in the motorcycle’s systems.
- Clear codes (if necessary): After taking note of the codes and addressing any issues, you can clear the codes using the scanner, resetting the system.
Following these steps can help you monitor the health of your Harley and ensure it runs optimally.
Expandable Lists of Trouble Codes by Category
ABS codes (C)
- P1142: Left front ABS wheel speed sensor input
- P1143: Right front ABS wheel speed sensor input
- P1144: Left rear ABS wheel speed sensor input
- P1145: Right rear ABS wheel speed sensor input
- P1252: ABS pump motor fault
COM codes (U)
- P1575: Security module input voltage high
- P1541: Data radio error
- P1584: Data link connector communication error
- P1554: Faulty communication with ECM/TCM
ECM codes (P)
- P0300: Random/multiple cylinder misfire detected
- P0113: Intake air temperature sensor high input
- P0131: O2 sensor circuit low voltage (bank 1)
- P0201: Injector circuit/open (cylinder 1)
RAD codes (B)
- P0480: Fan 1 control circuit
- P0481: Fan 2 control circuit
- P1492: ECT sensor circuit low
- P1495: Engine coolant temperature under-temperature
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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, so skilled, trained 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.
Harley-Davidson Code FAQs
1. What do the codes on a Harley-Davidson mean?
The diagnostic trouble codes (DTCs) on a Harley-Davidson indicate specific issues detected by the motorcycle's electronic control systems. Each code signals a potential fault within various systems, such as the engine, braking or body control module, helping with further diagnostic work.
2. How can I check the codes on my Harley-Davidson?
To check the codes on your Harley-Davidson, ensure the ignition is in the "on" position while holding down the trip reset button. This allows you to cycle through the modules on the dashboard, revealing any stored trouble codes that need to be addressed.
3. Are there any common Harley-Davidson codes I should be aware of?
Yes, some common Harley-Davidson codes include those related to the anti-lock braking system (ABS), engine control module (ECM) and fuel injection faults. Being familiar with these codes can help you identify and troubleshoot issues before they require professional service.
4. How can I prevent my Harley-Davidson from generating error codes?
Regular maintenance and timely inspections are essential in preventing your Harley-Davidson from generating error codes. Keeping the motorcycle's systems well-tuned, addressing minor issues promptly and ensuring the electrical connections are secure can help reduce the likelihood of trouble codes appearing.
5. Why is my Harley-Davidson's check engine light on?
The check engine light on your Harley-Davidson is on because of a detected fault within its onboard diagnostic system. This can be due to various reasons, from minor issues to significant faults. It’s essential to identify the associated trouble code to diagnose the problem accurately.
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Train for the Motorcycle Industry at MMI
If you want to become a motorcycle mechanic, then you’ve got to understand what to do with a Harley Davidson code list, as well as other key industry topics. Interested? Apply for Motorcycle Mechanic Institute’s 48-week Motorcycle Technician training program!7
While enrolled, you’ll be taught the foundations of motorcycle, ATV, side-by-side and personal watercraft systems to prepare to pursue a career as a motorcycle technician.1.1
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