P0318 – Rough Road Sensor “A” Signal Circuit means the engine control unit has detected a fault in the rough-road detection signal coming from Sensor “A.” This system helps the ECU distinguish between true engine misfires and vibrations caused by rough or uneven road surfaces. When the signal is missing, erratic, or out of range, misfire detection becomes unreliable and the ECU sets P0318. This guide explains what P0318 means, the symptoms, causes, diagnosis steps, and the most effective repair solutions to restore proper system operation.
What Does P0318 Mean?
P0318 is a generic OBD-II trouble code indicating the ECU is receiving an invalid or missing signal from the rough-road sensor “A.” Depending on the vehicle, this sensor may be a suspension-mounted accelerometer, a body-mounted G-sensor, or a processed signal from the ABS/ESC system through wheel speed variation analysis.
Without this input, the ECU cannot properly filter out road-induced vibrations, which may lead to false misfire readings, incorrect diagnostics, or reduced stability control accuracy.
Quick Reference
- OBD-II Family: P-Code (Powertrain)
- Scope: Generic
- System: Rough Road Detection / ABS / ESC / Sensor Input
- Difficulty Level: Moderate
- Estimated Repair Cost: €80–€300+
- Last Updated: 8 December 2025
Real-World Example / Field Notes
A crossover SUV arrived with P0318 and intermittent misfire codes that did not match drivability symptoms. The rough-road accelerometer connector under the rear seat had corrosion. After cleaning and applying dielectric grease, the sensor signal returned to normal and P0318 cleared.
Another vehicle set P0318 after suspension work. The wiring harness near the front strut had been stretched and partially torn. Repairing the harness and securing it properly restored the rough-road signal, eliminating false misfire codes.
Symptoms of P0318 – Rough Road Sensor “A” Signal Circuit
- Check engine light: Most common symptom.
- False misfire codes: ECU may misinterpret bumps as engine misfires.
- Intermittent traction or ABS warnings: If the signal interacts with ESC logic.
- Erratic misfire detection: Hard acceleration or rough surfaces may trigger false faults.
- No noticeable drivability issues: Engine typically runs normally.
Common Causes of P0318
Most Common Causes
- Faulty rough-road sensor (accelerometer or G-sensor)
- Damaged sensor wiring or corroded connectors
- ABS module not transmitting proper rough-road data
- Incorrect or missing sensor calibration after repair
- Loose or unplugged sensor connection
Less Common Causes
- Incorrect wheel/tire sizes causing incorrect vibration interpretation
- Failed ABS/ESC module
- Software mismatch after PCM or ABS programming
- Chassis wiring harness damage (rust, impact, debris)
- Sensor “A” internal failure from moisture or vibration
Diagnosis: Step-By-Step Guide
Whether the sensor is standalone or ABS-integrated, diagnosing P0318 requires checking wiring, signal integrity, and module communication.
Tools You’ll Need
OBD-II scanner with ABS/ESC access, multimeter, wiring diagrams, scan tool capable of module coding, and basic hand tools.
- Check freeze-frame data: See when the fault occurred and at what speed or road condition.
- Scan the ABS/ESC system: Look for wheel speed or accelerometer-related codes.
- Locate rough-road sensor “A”: Usually mounted on the body, frame, or suspension.
- Inspect wiring and connector: Look for corrosion, broken wires, moisture intrusion, or loose connections.
- Test sensor voltage supply: Verify power and ground are within specification.
- Check signal wire: Use a multimeter or oscilloscope to confirm stable sensor output.
- Check ABS module communication: Ensure rough-road data is being transmitted to PCM.
- Verify module coding: After ABS or PCM replacement, coding may be required.
- Inspect suspension wiring: Ensure no damage from recent repairs or terrain impact.
- Road test on smooth and rough surfaces: Monitor sensor data for proper signal response.
Pro Tip: Many rough-road sensors are shared with stability control systems—ABS codes often point directly to the underlying cause of P0318.
Possible Fixes & Repair Costs
- Replace rough-road/accelerometer sensor: €80–€180
- Repair corroded or damaged wiring: €50–€150
- Replace wheel speed sensor (if ABS-derived): €40–€120
- Reprogram or initialize ABS module: €80–€150
- Replace ABS/ESC module: €150–€300+
Can I Still Drive With P0318?
Yes, the vehicle typically drives normally. However, misfire detection accuracy is reduced, meaning the ECU may incorrectly set misfire codes or fail to detect real misfires. Traction and stability control function normally unless other ABS-related faults are present. It’s safe to drive temporarily, but proper diagnosis should not be delayed.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
Key Takeaways
- P0318 indicates a fault in the rough-road sensor “A” signal circuit.
- The most common causes are wiring issues, sensor failure, or ABS communication faults.
- Driving is usually safe, but misfire detection becomes unreliable.
- Fixing ABS/ESC or wiring problems often clears the code automatically.
FAQ
What is the rough-road sensor?
It is an accelerometer or stability sensor used by the ECU to distinguish road vibrations from actual engine misfires.
Is P0318 related to ABS problems?
Often yes. Many vehicles use ABS wheel speed data as the rough-road input, so ABS faults can trigger P0318.
Can incorrect tire sizes cause P0318?
Yes. Mismatched tires can distort vibration interpretation and disrupt rough-road logic.
Does P0318 cause misfires?
No. The engine may run perfectly, but the ECU cannot properly validate misfire readings without rough-road data.
How do I fix P0318 permanently?
Repair the sensor wiring, replace the faulty rough-road sensor, or correct ABS/ESC communication issues. Module reprogramming may also be required.