C1110

What Does Code C1110 Mean?

The diagnostic trouble code C1110 signifies an electrical fault within the Anti-lock Braking System’s (ABS) power relay coil circuit. This code is typically set by the Electronic Brake Control Module (EBCM) or Hydraulic Control Unit (HCU), which is the dedicated control unit for the ABS system, although some manufacturers may report it through the Powertrain Control Module (PCM). The EBCM is responsible for monitoring the integrity and functionality of the ABS system’s various components, including the power relay. The ABS power relay is a critical component that supplies electrical power to the ABS pump motor and/or the solenoid valves within the hydraulic modulator unit. When the EBCM detects an anomaly such as an open circuit, a short to ground, a short to voltage, or an out-of-specification resistance within the relay’s coil circuit, it interprets this as a failure, stores the C1110 code, and illuminates the ABS warning light. This fault prevents the EBCM from reliably controlling or engaging the ABS system, rendering the anti-lock braking function inoperative.

Common Symptoms

• ABS warning light illuminated on the instrument cluster.
• Traction control warning light illuminated, as these systems are often integrated and a fault in one impacts the other.
• Inoperative or reduced ABS function, meaning the wheels may lock up during hard braking similar to a non-ABS vehicle.
• Potentially a stiffer or unusual brake pedal feel under certain braking conditions if the system attempts to activate with a fault.

What Causes the Code C1110?

• Faulty ABS power relay: The relay itself may have an internal failure, such as an open or shorted coil winding, preventing it from activating or deactivating properly.
• Wiring harness issues: An open circuit (break), short to ground, or short to voltage in the wiring connecting the EBCM to the ABS power relay coil. This can be due to damaged insulation, corrosion, or a severed wire.
• Corrosion or poor connection at the relay socket: High resistance or intermittent contact at the relay’s terminals can disrupt the coil circuit.
• Blown fuse: A fuse providing power to the relay’s coil control circuit or to the EBCM’s internal relay control driver can fail.
• Faulty Electronic Brake Control Module (EBCM/HCU): Although less common than relay or wiring issues, an internal failure within the EBCM, such as a defective driver circuit for the relay coil, can also cause this code.

How to Diagnose and Troubleshoot

Diagnosis of C1110 requires a methodical approach using a digital multimeter (DMM), an appropriate OBD-II scanner, and detailed wiring diagrams specific to the vehicle.

1. Visual Inspection:
   • Begin by visually inspecting the ABS power relay, its electrical connector, and the surrounding wiring harness for any signs of physical damage, corrosion, fraying, or loose connections.
   • Locate and inspect all fuses related to the ABS system, especially those supplying power to the ABS module and the ABS relay coil. Check for continuity with a DMM if unsure.
2. Scan Tool Data Analysis:
   • Connect an OBD-II scanner capable of communicating with the ABS module. Retrieve all stored and pending Diagnostic Trouble Codes (DTCs).
   • If available, monitor ABS live data parameters, specifically looking for any relay status indicators or commands from the EBCM. Observe if the EBCM is attempting to command the relay ON/OFF.
3. ABS Power Relay Testing (DMM):
   • Relay Coil Resistance Test: With the ignition OFF, carefully remove the ABS power relay. Identify the coil terminals (typically pins 85 and 86 on a standard Bosch-style relay). Using a DMM set to ohms, measure the resistance across these two terminals. Compare the reading to the manufacturer’s specifications (usually between 60-120 ohms). An open circuit (showing “OL” or infinite resistance) or a reading significantly outside the specified range indicates a faulty relay coil.
   • Relay Activation Test: You can bench test the relay by applying 12V and ground to the coil terminals (85 and 86) and checking for continuity across the switch terminals (30 and 87). A click should be heard, and continuity should be present when activated.
4. Wiring Harness Continuity and Voltage Drop Tests:
   • Power Supply to Coil: With the relay removed and ignition ON (or as per wiring diagram), use the DMM to check for 12V at the appropriate power supply terminal for the relay coil in the relay socket.
   • Ground Control from EBCM: If the EBCM controls the ground side of the relay coil, verify continuity from the relay socket’s ground control pin to the EBCM connector. Then, with the EBCM commanded ON (if possible via scan tool) or during a self-test, check for a good ground at this pin in the relay socket.
   • Circuit Integrity: Disconnect both the EBCM connector and the ABS relay. Using the DMM, perform a continuity test between the corresponding pins of the relay socket and the EBCM connector for the relay coil circuit. Check for any shorts to ground or shorts to power in these wires.
5. EBCM Output Test (Advanced): If the relay and all wiring test good, and the EBCM is commanding the relay, but no voltage or ground is present at the relay coil circuit, the EBCM’s internal driver for the relay coil may be faulty. This requires further advanced diagnostics or a qualified technician.

Recommended Repairs and Solutions

Once the root cause of the C1110 code has been accurately identified through diagnosis, the following repairs are typically performed:

• Replace the ABS power relay: If the relay itself is found to be faulty (failed resistance test, no click during activation, etc.), replacement with a new, OEM-specified relay is the primary solution. Ensure the new relay has the correct amperage rating and pin configuration.
• Repair or replace damaged wiring: If the wiring harness connected to the ABS relay coil circuit is found to have an open, short, or high resistance, carefully repair the damaged section using appropriate automotive-grade wire, connectors, and heat shrink tubing. For extensive damage, replacing the relevant section of the harness may be necessary.
• Clean relay socket terminals: If corrosion or poor terminal tension is identified at the relay socket, carefully clean the terminals using electrical contact cleaner and a small brush. If terminals are spread, re-tension them carefully. Apply a thin layer of dielectric grease to prevent future corrosion.
• Replace blown fuses: If a fuse powering the relay control circuit is found to be blown, replace it with a new fuse of the correct amperage. Investigate why the fuse blew, as it may indicate an underlying short circuit.
• Replace the Electronic Brake Control Module (EBCM/HCU): This should be considered a last resort, only after meticulously confirming that the ABS relay, all associated wiring, and power/ground supplies are unequivocally functional. EBCM replacement often requires specialized programming or calibration procedures using a factory scan tool or equivalent, which is typically performed by a dealership or a specialist repair shop.

After any repair, clear the C1110 code using an OBD-II scanner, perform a road test under varying conditions to confirm the ABS system operates correctly, and ensure the code does not return. It’s crucial to verify the ABS warning light extinguishes and remains off.