C1920

What Does Code C1920 Mean?

The diagnostic trouble code C1920, typically a manufacturer-specific code (often related to Body, Chassis, or Network systems rather than Powertrain), signifies a “LED #1 Circuit Failure”. This indicates that a specific control module within the vehicle has detected an electrical fault within the circuit responsible for illuminating a particular Light-Emitting Diode (LED), designated as “LED #1”. The identity and function of “LED #1” are entirely dependent on the vehicle manufacturer and model, but it commonly refers to an indicator lamp within the instrument cluster, a control panel, or another interior/exterior lighting indicator controlled by a dedicated module. The controlling module, which could be the Body Control Module (BCM), Instrument Cluster Control Module (ICM), or a specialized Lighting Control Module (LCM), monitors the electrical characteristics of this circuit, such as voltage drop, current draw, or resistance. When these parameters fall outside the programmed acceptable range – indicating an open circuit, a short to ground, a short to voltage, or an incorrect load – the module registers the C1920 code and stores it in its memory.

Common Symptoms

• The specific indicator LED (LED #1) fails to illuminate when commanded.
• Intermittent illumination or flickering of the affected LED.
• Other related warning lights or indicators within the same module might malfunction due to shared power or ground circuits, or an internal module fault.
• Error messages or warnings displayed on the vehicle’s multi-function display (MFD) or instrument cluster, indicating a lighting system fault.
• In rare cases, if the fault is a significant short, it could lead to other electrical component issues or fuse failures if not adequately protected.

What Causes the Code C1920?

• Faulty LED Component: The LED itself may have failed due to an internal break, burnout, or degradation, resulting in an open circuit or altered resistance.
• Wiring Harness Faults: An open circuit (break in the wire), a short circuit (wire touching ground or another voltage source), or excessive resistance within the wiring harness connecting the control module to the LED.
• Corroded or Loose Electrical Connections: Poor pin tension, corrosion, or contamination at the connector terminals for the LED or at the control module, leading to intermittent contact or high resistance.
• Faulty Control Module: The internal driver circuit or output stage within the Body Control Module (BCM), Instrument Cluster Control Module (ICM), or relevant lighting control module responsible for powering LED #1 has failed.
• Incorrect Component Installation: Installation of an aftermarket or incompatible LED or component assembly with incorrect electrical specifications, causing the module to detect an abnormal load.

How to Diagnose and Troubleshoot

Diagnosis of C1920 requires a methodical approach, often involving a manufacturer-specific diagnostic scanner and a digital multimeter (DMM).

1. Retrieve Freeze Frame Data: Connect a suitable OBD-II diagnostic scanner capable of accessing Body/Chassis codes. Note any associated freeze frame data, which may provide clues regarding the operating conditions when the fault occurred.
2. Identify LED #1: Consult the vehicle’s specific factory service manual or wiring diagrams to precisely identify which physical LED corresponds to “LED #1” and which control module is responsible for its operation. This is critical as the generic code does not specify its location or function.
3. Visual Inspection:
   • Carefully inspect the identified LED and its surrounding assembly for visible damage, discoloration, or signs of burning.
   • Examine the wiring harness leading to the LED and the control module for any signs of chafing, pinching, corrosion, or breaks. Pay close attention to areas where the harness passes through grommets or near moving parts.
   • Inspect all associated electrical connectors for corrosion, bent pins, loose connections, or improper seating.
4. Electrical Circuit Testing with DMM:
   • Continuity Test (Open Circuit Check): With the battery disconnected and both ends of the circuit (at the control module and the LED assembly) unplugged, use the DMM to check for continuity of the power and ground wires between the control module connector and the LED connector. Any reading of OL (Open Line) indicates a break in the wire.
   • Resistance Check of LED: If the LED is accessible and separable, measure its resistance. Compare this reading to factory specifications. An open circuit (OL) indicates a failed LED. (Note: LEDs are diodes, so resistance may vary depending on polarity, but an open circuit is typically clear).
   • Short to Ground/Voltage Check: With the circuit disconnected from the module and the LED, use the DMM in resistance mode to check for continuity between the LED circuit wires and vehicle chassis ground, and between the LED circuit wires and any constant/switched 12V supply wires. Any low resistance reading indicates a short.
   • Voltage Supply Check: With the control module connected and powered (and the LED commanded ON via scan tool if possible), use the DMM to verify that the specified voltage (typically 12V or a lower regulated voltage) is present at the LED’s power input terminal and that a proper ground exists at its ground terminal.
   • Voltage Drop Test: If the circuit appears to have continuity but the LED is dim or non-functional, perform a voltage drop test across sections of the circuit, including connectors, while the circuit is active. Excessive voltage drop (>0.2V) indicates high resistance.
5. Control Module Actuator Test: If your diagnostic scanner supports it, attempt to perform an “actuator test” or “output control” to command LED #1 ON/OFF. If the module reports successful activation but the LED does not illuminate, the fault lies in the LED or its wiring. If the module reports a failure to activate, the fault is likely within the module itself or the immediate wiring from the module.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Repair or Replace Wiring: If the DMM tests confirm an open circuit, short, or high resistance in the wiring harness, the damaged section of the wire should be repaired using proper automotive wiring repair techniques (e.g., soldering and heat shrink tubing) or the entire harness section replaced if the damage is extensive.
• Clean and Secure Connections: If corrosion or loose terminals are found, disconnect the battery, thoroughly clean the affected terminals using electrical contact cleaner and a small brush, and ensure the connectors are fully seated and securely latched. If pins are bent or splayed, carefully reshape or replace them.
• Replace Faulty LED or Assembly: If the LED itself is confirmed to be failed (e.g., open circuit), it should be replaced. Depending on the vehicle, this may involve replacing an individual LED, a small circuit board containing the LED, or a larger assembly such as the entire instrument cluster or control panel where the LED resides.
• Replace Control Module: If all wiring and LED components test good, and the control module’s internal driver circuit is suspected to be faulty (e.g., failed actuator test where the module reports failure to activate), the relevant control module (BCM, ICM, LCM) will need to be replaced. Be aware that module replacement often requires programming or calibration using a specialized factory scan tool.
• Verify Repair: After any repair, clear the C1920 code from the control module’s memory, operate the vehicle and the affected LED repeatedly to ensure proper function, and re-scan for codes to confirm the fault does not return.