C1955

What Does Code C1955 Mean?

Diagnostic Trouble Code C1955 indicates an open circuit condition within the Steering Angle Sensor (SAS) circuit. The Steering Angle Sensor is a critical input device for various vehicle dynamic control systems, primarily the Electronic Stability Control (ESC) module (also known as the ABS/ESC module). This sensor measures the rotational position of the steering wheel and transmits this real-time data to the control modules, often via a CAN (Controller Area Network) bus. An “open circuit” signifies a complete break in the electrical continuity of the sensor’s wiring, its internal components, or its connector. This interruption prevents the necessary electrical signal or power from reaching the sensor or the control module, effectively rendering the sensor inoperative from the module’s perspective. When the ABS/ESC module detects this absence of signal or an abnormal electrical characteristic consistent with an open circuit on the SAS input, it sets code C1955. This code directly impacts the functionality of safety systems that rely on steering input, such as ESC, Traction Control System (TCS), and in some vehicles, Electric Power Steering (EPS) and Advanced Driver-Assistance Systems (ADAS) like lane-keeping assist or adaptive cruise control.

Common Symptoms

• Electronic Stability Control (ESC) Light / Traction Control System (TCS) Light Illuminated: This is the most prevalent symptom, as the SAS is fundamental to these systems.
• Antilock Brake System (ABS) Warning Light Illuminated: Since the ESC system often integrates with the ABS module, a fault in a critical sensor like the SAS can trigger related ABS warnings.
• Inoperative or Degraded Electronic Stability Control/Traction Control: The vehicle’s ability to prevent skidding or wheel slip will be compromised due to the lack of steering input.
• Difficulty with Steering or Erratic Power Steering Operation: On vehicles with Electric Power Steering (EPS) that utilize SAS data for assist calculations, an open circuit can cause reduced assist or unpredictable steering feel.
• Deactivation of Advanced Driver-Assistance Systems (ADAS): Features like lane departure warning, lane keeping assist, or adaptive cruise control may become unavailable.
• Steering Wheel Feels Loose or Unresponsive: While less common for an open circuit directly, a loss of EPS functionality tied to the SAS can indirectly lead to this perception.

What Causes the Code C1955?

• Faulty Steering Angle Sensor (SAS): Internal electrical failure within the sensor, leading to an open circuit.
• Damaged Wiring Harness: A physical break, chafing, or corrosion in the wires connecting the SAS to the ABS/ESC module or other relevant control units.
• Corroded or Loose Electrical Connectors: Poor contact or corrosion at the SAS connector itself, or at the module connector, creating an open path.
• Faulty Clock Spring: The clock spring assembly, which allows for continuous electrical connection to components on the steering wheel while it rotates, often houses or provides the circuit path for the SAS. An internal open circuit within the clock spring can cause C1955.
• Blown Fuse: Although less common for a specific “open circuit” code, if the power supply circuit to the SAS is fused and that fuse blows, it will prevent the sensor from operating and signal generation, effectively causing an open circuit condition from the module’s perspective.

How to Diagnose and Troubleshoot

Diagnosing C1955 requires a methodical approach, utilizing a digital multimeter (DMM) and an advanced OBD-II scan tool capable of accessing ABS/ESC module data.

1. Retrieve All DTCs: Use an advanced scan tool to read all Diagnostic Trouble Codes from the ABS/ESC module and other relevant modules (e.g., PCM, EPS). This can reveal if there are other related codes that might point to a broader electrical issue or module failure.
2. Visual Inspection:
   • Inspect the wiring harness leading to the Steering Angle Sensor (typically located behind the steering wheel or within the steering column assembly) for any visible damage, chafing, cuts, or signs of corrosion.
   • Carefully inspect the electrical connectors at the SAS and the ABS/ESC module for bent pins, corrosion, or looseness.
   • Check for any recent work done on the steering column or airbag system that might have disturbed the SAS or its wiring.
3. Steering Angle Sensor (SAS) Live Data Check (if accessible): With the scan tool, attempt to view live data from the SAS. If the circuit is truly open, the sensor’s value will likely show a static, abnormal reading (e.g., 0 degrees, a fixed maximum value, or simply no data).
4. Digital Multimeter (DMM) Testing:
   • Disconnect Battery: For safety, especially when working near airbags and clock springs, disconnect the vehicle’s battery.
   • Isolate the SAS: Disconnect the electrical connector from the Steering Angle Sensor.
   • Power and Ground Check: Using the vehicle’s wiring diagram, identify the power and ground pins at the SAS connector (vehicle side). Reconnect the battery temporarily, turn the ignition to ON (engine OFF), and check for appropriate voltage (typically 5V or 12V, consult diagram) and a good ground signal using your DMM. If power or ground is missing, troubleshoot the respective circuit back to its source (fuse box, module).
   • Continuity Test on SAS Wiring Harness: With the battery disconnected and both the SAS and the ABS/ESC module connectors disconnected, identify the signal wires for the SAS. Test for continuity of each wire from the SAS connector to the ABS/ESC module connector. An “open circuit” will show infinite resistance (OL or ‘Open Line’ on most DMMs), indicating a break in that specific wire.
   • Steering Angle Sensor Internal Resistance Check: If specifications are available, measure the resistance across the SAS’s internal pins (sensor side). An open circuit within the sensor itself will show infinite resistance.
   • Clock Spring Continuity Check: If the SAS signal or power runs through the clock spring, disconnect the clock spring’s connectors and test for continuity of the relevant circuits through the clock spring as per the wiring diagram. An open in the clock spring’s internal ribbon cable can cause C1955.
5. Fuse Inspection: Locate and inspect any fuses that supply power to the Steering Angle Sensor or the clock spring. Replace any blown fuses, but be aware that a blown fuse often indicates an underlying short circuit.

Recommended Repairs and Solutions

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

• Repair or Replace Damaged Wiring: If the visual inspection or continuity tests reveal a break or damage in the wiring harness, repair the specific section using appropriate automotive wiring repair techniques (soldering, heat shrink tubing) or replace the entire harness if damage is extensive.
• Clean or Replace Corroded Connectors: If corrosion or poor contact is found at the SAS or module connectors, attempt to clean them thoroughly with electrical contact cleaner. If pins are severely corroded or bent, the connector (or relevant pigtail) should be replaced.
• Replace the Steering Angle Sensor: If DMM tests indicate an internal open circuit within the SAS itself, the sensor is faulty and requires replacement. Ensure you obtain the correct part number for your vehicle.
• Replace the Clock Spring: If continuity tests through the clock spring indicate an open circuit, the clock spring assembly must be replaced. This often involves airbag system disassembly, which should only be performed by qualified personnel following strict safety procedures.
• Perform SAS Calibration: After replacing the Steering Angle Sensor or clock spring, it is almost always necessary to perform a steering angle sensor calibration (or zero-point calibration) using an advanced scan tool. Failing to do so will often result in persistent warning lights and improper system operation, even if the hardware fault is resolved.
• Clear Codes and Road Test: After completing repairs and calibration, clear all DTCs from all modules. Perform a comprehensive road test to confirm that C1955 does not return and that all affected systems (ESC, TCS, EPS, ADAS) are functioning correctly.