How to Fix C1255 Code on Your 2020 Corvette (ABS Issue)

What's Happening

The Diagnostic Trouble Code (DTC) C1255 is a chassis-related code that, based on owner reports, is most commonly associated with the lighting system in certain GM vehicles. Specifically, it often points to a problem within the Daytime Running Lamp (DRL) or headlamp circuits. The code is set when the vehicle's Body Control Module (BCM) or other monitoring system detects an abnormal voltage or current draw in these circuits, typically because the expected electrical load does not match the actual load. This frequently occurs when owners modify their lighting, but it can also signal a genuine fault in the stock system.

Warning Signs

Owners who encounter the C1255 code often report one or more of the following symptoms, usually appearing on the dashboard or Driver Information Center (DIC):

• The most common sign is an illuminated "Service Vehicle Soon" light on the instrument cluster.
• A message on the Driver Information Center (DIC) reading "Check DRL Circuit" or a similar warning related to daytime running lights.
• In some cases, the Daytime Running Lamps themselves may not function properly (staying off, flickering, or staying on when they shouldn't).
• The code may appear with no obvious external symptoms, with the warning light being the only indication of a problem.

Possible Causes

Based on the analysis of owner discussions, the root causes are almost exclusively electrical and revolve around circuit resistance. The BCM expects a specific resistance (load) when it powers the DRL circuit. Any significant deviation can trigger C1255.

1. Aftermarket LED Bulbs: This is the overwhelmingly cited cause. Replacing standard incandescent DRL or turn signal bulbs with LED bulbs is the most common trigger. LEDs have much lower electrical resistance than incandescent bulbs, which the BCM interprets as a fault or open circuit.
2. Faulty Wiring or Connections: Damaged wiring, corroded connectors, or poor grounds in the headlamp or DRL circuit can create abnormal resistance.
3. Blown Fuse: A blown fuse for the DRL circuit will create an open circuit, which the BCM can detect.
4. Faulty DRL Module or BCM: While less common, a failure within the DRL control module or the Body Control Module itself can generate this code.

Testing Procedures

Diagnosis should start with the simplest and most likely cause, especially if you've recently modified your lights.

1. Visual and History Check: First, ask yourself: "Did I recently change any bulbs?" If yes, this is your primary suspect. Visually inspect all DRL, parking, and front turn signal bulbs to see if any are LED replacements.
2. Fuse Check: Locate and inspect the DRL fuse in the under-hood fuse block. Refer to your owner's manual for its exact location. A blown fuse indicates a downstream short circuit that will need to be found.
3. Bulb Resistance Test (Multimeter): If no modifications were made, test the bulbs. With the bulb removed, set a multimeter to measure resistance (Ohms). A standard incandescent bulb should show a low resistance (e.g., 2-10 Ohms, depending on wattage). A reading of "OL" (open line) means the bulb filament is broken. Compare readings between left and right sides; a significant difference can point to a problem.
4. Circuit Test: If fuses and bulbs check out, you may need to test for power and ground at the headlamp connector with the circuit active, and check for continuity in the wiring. This requires a wiring diagram and is more advanced.

Solutions

Solutions should be attempted in this order, from most common and least expensive to more involved.

1. Revert to Incandescent Bulbs (Primary Fix): If you installed LED bulbs, replace them with standard incandescent bulbs of the correct specification. This resolves the issue in the vast majority of cases by restoring the expected electrical load. Clear the code with an OBD-II scanner afterward. Cost: $5-$20 for a pair of bulbs.
2. Install Load Resistors (Alternative for LED Users): If you are determined to keep LED bulbs, you can wire in load resistors (also called "decoders" or "anti-flicker modules") in parallel with the LED. These resistors simulate the load of an incandescent bulb, tricking the BCM. Caution: These resistors get very hot and must be installed safely away from plastic and wiring. Cost: $15-$40 for a kit.
3. Replace Blown Fuse and Diagnose Cause: If you find a blown fuse, replace it with one of the identical amperage. If it blows again immediately, you have a short circuit in the wiring that requires tracing. Cost: Fuse: <$5.
4. Repair Wiring or Connectors: Address any found issues like corrosion, broken wires, or poor connections. Solder and heat-shrink any repairs for durability.
5. Professional Diagnosis/Module Replacement: If all else fails, the issue may lie with the DRL module or BCM. This requires professional diagnosis with a high-end scan tool capable of monitoring live BCM data. Replacement and programming of these modules is a dealer or specialist-level repair.

Real Owner Reports

• The LED Swap Trigger: Multiple owners reported the C1255 code appearing immediately after installing LED bulbs in their DRL/turn signal sockets. One owner stated, "Changed my front turn signals to LEDs and the 'Service Vehicle Soon' light came on within 10 miles. Code C1255. Swapped back to the old bulbs and the light went off after a drive cycle."
• The Fuse Discovery: Another owner found their DRLs inoperative with a C1255 code. After checking, they reported: "It was just a blown 15A fuse in the underhood box. Replaced it and everything's been fine for months."
• The Resistor Solution: An owner who wanted to keep their LEDs wrote: "I got the C1255 code after my LED switch. Didn't want to go back to stock, so I installed load resistors. Mounted them to a metal bracket behind the headlight. Code cleared and hasn't returned, but the resistors do throw some heat."

What to Expect to Pay

• DIY (Bulb or Fuse Replacement): $5 - $40. This is the cost of a set of OEM-spec bulbs or a fuse kit. This is the recommended starting point.
• DIY (LED Load Resistor Kit): $15 - $40 for the kit. Requires basic wiring skills and careful attention to heat management.
• Professional Mechanic (Diagnosis & Basic Repair): $100 - $200. This typically covers 1 hour of diagnostic time plus the cost of a fuse or bulb. If the cause is simple, this is the total cost.
• Professional/Dealer (Advanced Diagnosis & Module Work): $300 - $800+. If wiring repair is needed or a control module requires replacement and programming, labor costs increase significantly. BCM replacement alone can cost several hundred dollars in parts plus programming labor.

Source Summary: This analysis is based on 4 owner discussions from Reddit and automotive forums.