C1117

What Does Code C1117 Mean?

DTC C1117 signifies an “RPM Input Circuit Failure,” indicating that a specific control module, typically the Anti-lock Brake System (ABS) module, Traction Control System (TCS) module, or another chassis-related module, has detected an issue with the electrical circuit providing engine RPM (Revolutions Per Minute) data. This is a chassis-specific code, meaning the fault lies within the communication or signal acquisition path for engine RPM data to a chassis system, rather than a primary engine control (P-code) directly related to the engine’s RPM sensor function itself. The module setting this code expects a reliable engine RPM signal to perform its functions, such as engine torque reduction during traction control events, stability control interventions, or for proper transmission shift logic. When the module detects an RPM signal that is absent, erratic, implausible, or outside of its calibrated operating range for a specified duration or under specific driving conditions, it will set the C1117 code. This detection is based on monitoring the voltage or digital signal input on the dedicated RPM circuit or the CAN (Controller Area Network) bus for consistency and validity.

Common Symptoms

• Illuminated Warning Lights: The most common symptom is the illumination of the ABS warning light, Traction Control System (TCS) warning light, or Stability Control System (SCS) warning light on the instrument cluster.
• Reduced Engine Performance or Limp Mode: In some vehicles, the ABS/TCS module may request the Powertrain Control Module (PCM) to reduce engine power (limp-home mode) if it determines it cannot safely manage traction without accurate RPM data.
• Inoperative Traction Control/Stability Control: The ABS/TCS system may be disabled, preventing it from intervening during wheel slip or loss of stability.
• Incorrect Transmission Shifting: Some transmission control modules rely on engine RPM data for accurate shift points. If the chassis module’s RPM input is compromised, it could indirectly affect transmission performance, leading to harsh shifts or incorrect gear selection.
• Lack of Engine Torque Reduction: During wheel spin, the system might fail to reduce engine torque, potentially leading to uncontrolled acceleration or instability.

What Causes the Code C1117?

• Wiring Harness Issues: An open circuit, short to ground, short to power, or excessive resistance in the dedicated RPM signal wire(s) leading to the module setting the code (e.g., ABS module) or in the CAN bus wiring.
• Corroded or Loose Connectors: Poor electrical contact at the engine RPM sensor connector, PCM connector, or the module’s connector itself (e.g., ABS control module).
• Faulty Engine RPM Sensor (Crankshaft Position Sensor – CKP or Camshaft Position Sensor – CMP): While C1117 is a chassis code, if the sensor’s signal is directly fed to the chassis module (less common in modern vehicles) or if its primary signal failure prevents the PCM from broadcasting correct RPM data, it can be an indirect cause. More commonly, a good sensor signal isn’t making it to the specific module.
• Internal Module Failure: A defective component within the module setting the code (e.g., ABS control module, TCS module) rendering it unable to correctly receive or interpret the RPM input signal.
• CAN Bus Communication Failure: An issue on the CAN bus network preventing the module from receiving engine RPM data broadcasted by the PCM. This could involve damaged bus wires, incorrect terminating resistors, or a faulty module interfering with bus communication.

How to Diagnose and Troubleshoot

Diagnosis of C1117 requires a systematic approach, often involving an advanced scan tool and a digital multimeter (DMM).

1. Retrieve All DTCs and Freeze Frame Data: Connect an OBD-II scanner and retrieve all active and pending Diagnostic Trouble Codes (DTCs), especially U-codes (network communication issues) and any related P-codes (powertrain codes). Analyze freeze frame data to understand the operating conditions when the C1117 was set.
2. Visual Inspection: Carefully inspect the wiring harness and electrical connectors associated with the engine’s Crankshaft Position Sensor (CKP) and Camshaft Position Sensor (CMP), the Powertrain Control Module (PCM), and the module setting the C1117 code (e.g., ABS control module). Look for signs of damage, chafing, corrosion, loose pins, or environmental ingress.
3. Scan Tool Live Data Monitoring: With the engine running, monitor live data streams from the PCM for “Engine RPM” and, if available, monitor the RPM input signal received by the module that set C1117 (e.g., ABS module). Compare these values. Look for discrepancies, intermittent drops, or frozen readings in the chassis module’s RPM input.
4. Wiring Continuity and Resistance Testing:
   • Isolate the circuit: Disconnect the relevant connectors (e.g., ABS module connector and PCM connector, or CKP sensor connector).
   • Check for Opens: Use a DMM to check for continuity on the signal wire(s) from the PCM or CKP sensor to the module. An open circuit will show infinite resistance.
   • Check for Shorts: Test for shorts to ground and shorts to battery voltage on the signal wire. A short to ground will show very low resistance to ground; a short to power can be identified by measuring voltage on the signal wire with the ignition on and relevant circuits powered.
   • Check for Excessive Resistance: Measure the resistance of the signal wire(s). High resistance can attenuate the signal. Consult service information for expected resistance values.
5. CAN Bus Integrity Check (If suspected): If the RPM signal is transmitted via CAN bus, use a DMM to measure the resistance between CAN High and CAN Low wires at the DLC (Diagnostic Link Connector). Expect approximately 60 ohms with the ignition off, indicating proper bus termination. Discrepancies may indicate a wiring issue or a faulty terminating resistor.
6. Oscilloscope Analysis (Advanced): For intermittent or erratic signals, an oscilloscope (lab scope) is invaluable. Connect the scope to the RPM input signal wire at the module. Observe the waveform for proper amplitude, frequency, and any dropouts or noise while wiggling the harness or during a test drive.
7. Module Pin-Out and Power/Ground Verification: Using service information, verify that the module setting the code has proper power and ground inputs at its connector. Incorrect voltage or ground can affect its ability to process signals.

Recommended Repairs and Solutions

The repair strategy for C1117 depends directly on the root cause identified during diagnosis.

• Repair or Replace Damaged Wiring/Connectors: If visual inspection or DMM testing reveals damaged wires, corroded pins, or loose connections, repair them using appropriate automotive-grade connectors and wiring. Ensure all splices are properly sealed to prevent future corrosion.
• Replace Faulty Engine RPM Sensor: If diagnostic steps indicate that the primary Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP) is directly at fault (e.g., incorrect signal output confirmed with an oscilloscope), replace the sensor. Always use an OEM-equivalent or genuine part for critical sensors.
• Address CAN Bus Issues: If a CAN bus communication fault is identified (e.g., incorrect bus resistance, voltage irregularities), repair the damaged bus wiring, replace faulty terminating resistors, or identify and replace any module that is actively interfering with bus communication.
• Replace Faulty Control Module: If all wiring, sensor outputs, and communication lines are verified to be in perfect working order, and the module setting the C1117 code still fails to receive or process the RPM input, the module itself (e.g., ABS control module) is likely defective. Replacement of such modules often requires specialized programming or calibration using a factory-level scan tool.
• Clear Codes and Verify Repair: After any repair, clear all DTCs from all affected modules. Perform an extended test drive under various operating conditions to ensure the code does not return and that all systems are functioning correctly. Pay close attention to the conditions under which the original code was set (as per freeze frame data).