The P0318 OBD-II trouble code means the powertrain control module has detected a problem with the signal it uses from Rough Road Sensor “A.”

The generic definition is:

P0318 — Rough Road Sensor “A” Signal Circuit

Depending on the vehicle, Sensor A may be:

A dedicated rough-road accelerometer
A chassis acceleration sensor
A signal calculated by the ABS module
Data derived from wheel-speed sensors
A message transmitted through the CAN network

P0318 does not automatically mean one ABS wheel-speed sensor has failed. It also does not prove the engine is misfiring.

The code means the expected Sensor A rough-road signal is missing, implausible, interrupted or outside the manufacturer’s acceptable range.

The PCM uses that information to distinguish genuine combustion failures from crankshaft-speed disturbances caused by potholes, gravel and other uneven surfaces. Apparently, even the computer occasionally needs help deciding whether the engine stumbled or California finally stopped repairing the road.

P0318 belongs to the powertrain-code family covered in the complete Pro Street P-code OBD-II guide.

P0318 Quick Answer

Item	Information
Trouble code	P0318
Definition	Rough Road Sensor “A” Signal Circuit
System	Rough-road detection and misfire validation
Severity	Moderate
Safe to drive?	Usually briefly, unless ABS, stability-control or severe engine problems are present
Common causes	Sensor fault, wiring, wheel-speed data, module communication or incorrect configuration
First diagnostic step	Scan the PCM and all ABS/stability-control modules
Related codes	P0317, P0319, ABS wheel-speed codes and network U-codes
Typical repair range	Approximately $100 to $1,500+, depending on the cause

What Does P0318 Mean?

Modern engine computers detect combustion misfires partly by monitoring changes in crankshaft speed.

Each healthy combustion event accelerates the crankshaft. A weak or missing combustion event causes a measurable reduction in crankshaft acceleration.

Unfortunately, driving over an uneven road can also disturb the drivetrain and create sudden changes in crankshaft speed.

Rough-road detection helps the PCM determine whether those changes are caused by:

Actual engine misfire
Potholes
Gravel
Railroad crossings
Wheel hop
Wheel slip
Chassis movement
ABS or stability-control intervention

When the PCM detects a problem with its designated Rough Road Sensor A signal, it may store P0318.

The exact code-setting conditions vary by manufacturer.

The fault may involve:

Missing signal
Signal stuck high or low
Implausible sensor output
Intermittent signal
Open circuit
Short to voltage
Short to ground
Missing ABS data
Network communication failure
Incorrect module programming

What Is Rough Road Sensor A?

“Sensor A” is a system designation, not a universal physical location.

It does not necessarily mean:

Left-front wheel-speed sensor
First sensor in the engine bay
Sensor mounted on Bank 1
A component labeled Sensor A

The manufacturer decides which signal is designated Rough Road Sensor A.

Possible implementations include:

Dedicated Rough-Road Sensor

Some vehicles use an accelerometer or dedicated sensor mounted to the body or chassis.

It may measure:

Vertical movement
Chassis acceleration
Vibration
Road-surface disturbance

ABS-Based Rough-Road Calculation

Many vehicles use individual wheel-speed sensors and the ABS module.

The ABS module compares wheel-speed changes and calculates whether the vehicle is traveling over an uneven surface. It then sends rough-road information to the PCM.

Network-Based Signal

The PCM may receive a rough-road status message from:

ABS module
Electronic Brake Control Module
Stability-control module
Chassis-control module
Body Control Module

In these systems, P0318 may be caused by a communication or configuration problem rather than a conventional sensor circuit.

Factory service information is required to determine what Sensor A means on the specific vehicle.

Why Does the PCM Monitor Rough-Road Conditions?

The PCM uses crankshaft acceleration to identify combustion failures.

A pothole or uneven road may temporarily change:

Wheel speed
Drivetrain load
Engine speed
Crankshaft acceleration
Transmission output speed

Without rough-road information, the PCM might mistake those disturbances for an engine misfire.

The Sensor A signal allows the PCM to:

Modify misfire-monitor sensitivity
Temporarily suspend misfire counting
Prevent false P0300 codes
Avoid assigning the wrong cylinder-specific code
Improve emissions-monitor accuracy

P0318 therefore affects the system used to validate misfire data. It does not automatically indicate a genuine combustion problem.

P0318 Versus P0317

P0317 and P0318 are closely related but identify different faults.

Code	Meaning
P0317	Expected rough-road hardware or information is unavailable
P0318	Rough Road Sensor A’s signal or circuit is faulty

P0317 may result from:

Missing module
Incorrect module configuration
Hardware not recognized
Communication failure
Incompatible replacement controller

P0318 focuses more specifically on the Sensor A signal path.

Possible P0318 causes include:

Failed sensor
Damaged circuit
Implausible signal
Intermittent dropout
Incorrect sensor mounting
Missing wheel-speed data
Network message fault

When both codes appear, verify vehicle configuration and Sensor A operation before replacing components.

P0318 Versus P0319

P0318 and P0319 identify separate rough-road signal assignments.

Code	Meaning
P0318	Rough Road Sensor A Signal Circuit
P0319	Rough Road Sensor B Signal Circuit

A vehicle may use:

Two dedicated acceleration sensors
Multiple chassis sensors
Separate calculated data channels
Different ABS-derived signals
Manufacturer-specific A and B assignments

Do not assume Sensor A and Sensor B correspond to left and right sides.

Use factory wiring diagrams and module data definitions to determine what each designation represents.

P0318 Versus an ABS Wheel-Speed Code

P0318 is not the same as a code identifying one failed wheel-speed sensor.

Code group	General intent
P0318	Rough Road Sensor A signal used by the PCM
C0035–C0051	Individual wheel-speed sensor or circuit faults
U-codes	Communication failure between modules

A failed wheel-speed sensor may indirectly cause P0318 if the ABS module can no longer calculate rough-road conditions.

However, the wheel-speed fault should normally be confirmed through:

ABS codes
Live wheel-speed data
Sensor waveform
Circuit testing
Tone-ring inspection

For related chassis faults, visit the complete C-code OBD-II library.

Common Conditions Associated With P0318

A vehicle with P0318 may experience:

Check Engine Light
ABS warning light
Traction-control warning
Stability-control warning
Failed emissions inspection
Disabled or limited misfire monitoring
False or inconsistent misfire codes
Intermittent warnings over rough roads
Cruise-control problems on some applications
No noticeable drivability problem

P0318 itself usually does not cause rough idle, hesitation or engine shaking.

If the engine runs poorly, diagnose the combustion problem separately.

How Serious Is P0318?

P0318 is generally moderate in severity.

The engine may continue running normally because the fault commonly affects misfire validation rather than direct fuel or ignition control.

However, the code should be diagnosed because it may indicate:

Loss of rough-road information
ABS wheel-speed fault
Disabled stability-control function
Module communication failure
Incorrect controller programming
Inaccurate misfire monitoring
Wiring or connector damage

Stop Driving or Seek Immediate Service If:

ABS and brake warning lights appear together
Braking behavior changes
Several wheel-speed signals disappear
Stability-control operation becomes erratic
The engine develops a flashing Check Engine Light
Severe shaking or power loss occurs
Multiple modules stop communicating

P0318 alone does not prove that the ABS system has stopped working. Scan the ABS module and evaluate its warning indicators.

Most Common Causes of P0318

Possible cause	Relative likelihood
Damaged Sensor A wiring or connector	High
Faulty dedicated rough-road sensor	High where equipped
Missing or erratic ABS wheel-speed data	High on ABS-based systems
Damaged tone ring or magnetic encoder	Medium
CAN communication problem	Medium
Incorrect PCM or ABS module configuration	Medium after module work
Sensor mounted incorrectly	Medium after repair
Initialization or calibration not completed	Application dependent
Low system voltage or poor ground	Medium
ABS or chassis-control module fault	Lower
Crankshaft signal fault	Lower
PCM failure	Rare

The correct diagnostic path depends on how the vehicle generates Sensor A data.

How to Diagnose P0318

Step 1: Confirm P0318

Connect a professional scan tool capable of communicating with:

PCM or ECM
ABS module
Electronic Brake Control Module
Stability-control module
Chassis-control module
Body Control Module where applicable

Record:

Stored codes
Pending codes
Permanent codes
Freeze-frame data
Manufacturer-specific codes
Module communication status
Sensor A live data where available

Do not clear the codes yet.

A basic code reader may retrieve P0318 while missing the ABS or network code that reveals the actual failure.

Step 2: Scan Every Module

Check all available modules for:

Wheel-speed sensor codes
Accelerometer codes
Lost-communication codes
Low-voltage codes
Module-configuration faults
Sensor initialization faults
P0317
P0319
Misfire codes
Crankshaft position codes

Code combinations provide direction.

Code combination	Likely diagnostic direction
P0318 only	Identify and test the Sensor A data source
P0318 plus wheel-speed code	Diagnose that wheel-speed signal first
P0318 plus lost ABS communication	Test ABS power, ground and CAN circuits
P0318 plus P0317	Verify hardware configuration and Sensor A availability
P0318 plus P0319	Look for shared power, ground, module or network faults
P0318 after module replacement	Verify programming, configuration and initialization
P0318 plus low-voltage codes	Test battery, charging system, power and grounds

Step 3: Review Freeze-Frame Data

Record the conditions present when P0318 was stored:

Vehicle speed
Engine speed
Engine load
Battery voltage
Wheel-speed values
Brake-switch status
ABS activity
Stability-control activity
Road-surface status if available

Determine whether the code occurred:

During startup
At highway speed
Over an uneven road
During braking
During a turn
Immediately after a repair
During a low-voltage event

Step 4: Review Recent Repair History

Ask whether P0318 appeared after:

PCM replacement
PCM programming
ABS module replacement
Wheel-speed sensor replacement
Wheel bearing or hub replacement
Suspension repair
Collision repair
Brake repair
Battery failure or jump-start
Wiring repair
Tire or wheel changes

A code appearing immediately after repair should direct attention toward installation, configuration and disturbed wiring.

Step 5: Identify Sensor A

Use the correct factory service information to determine:

Whether Sensor A is physical or calculated
Sensor location
Supplying module
Wiring route
Connector pinout
Expected signal type
Calibration requirements
Communication path

Possible signal types include:

Analog voltage
Frequency
Pulse-width signal
Digital sensor output
CAN message
Calculated ABS status

Do not apply resistance or voltage tests until the sensor design is known. Sending test voltage into a communication circuit is a creative way to turn one code into several.

Diagnosing a Dedicated Rough-Road Sensor

Step 6: Inspect Sensor A Physically

If the vehicle uses a dedicated accelerometer or rough-road sensor, inspect:

Correct mounting location
Correct orientation
Tight fasteners
Physical damage
Connector engagement
Water intrusion
Corrosion
Harness condition
Signs of collision damage

Sensor orientation matters. An accelerometer mounted backward, upside down or on an incorrect bracket may report an implausible signal.

Step 7: Check Sensor Power and Ground

Using the wiring diagram, verify:

Reference or supply voltage
Ground quality
Signal circuit
Shielding where used

Test grounds using voltage drop whenever possible.

A ground circuit may show continuity while developing excessive resistance under load.

Step 8: Test the Sensor A Signal

The correct test depends on sensor type.

Possible procedures include:

Measuring resting signal voltage
Monitoring voltage during controlled movement
Checking frequency
Checking pulse width
Viewing an oscilloscope waveform
Comparing scan-tool data with physical movement

A healthy signal should respond consistently according to manufacturer specifications.

Watch for:

Signal fixed at zero
Signal fixed near supply voltage
Intermittent dropouts
Excessive electrical noise
No response to movement
Implausible response direction

Do not strike or shake the sensor unless the service procedure specifically allows it.

Diagnosing ABS-Derived Sensor A Data

Step 9: Verify ABS Module Communication

Attempt direct communication with the ABS or Electronic Brake Control Module.

If communication fails, inspect:

ABS fuses
Module power supply
Module grounds
CAN high circuit
CAN low circuit
Connectors
Water intrusion
Module condition

Do not replace the ABS module before confirming its power, ground and communication circuits.

Step 10: Monitor All Wheel Speeds

View individual wheel-speed data while:

Driving slowly
Driving straight
Turning
Accelerating gently
Decelerating
Crossing a controlled uneven surface where safe

All wheel speeds should respond smoothly and remain reasonably consistent during straight-line driving.

Look for:

One wheel remaining at zero
Sudden dropouts
Implausible spikes
One wheel reading differently
Signal loss during turns
Signal interruption over bumps

An erratic wheel-speed signal may prevent the ABS module from generating valid rough-road information.

Step 11: Inspect the Wheel-Speed Sensor

Inspect the affected sensor for:

Physical damage
Loose mounting
Excessive air gap
Metal debris
Corrosion
Connector damage
Chafed wiring
Water intrusion
Incorrect installation

Testing may include:

Supply voltage
Ground
Signal voltage
Frequency
Resistance on applicable passive sensors
Digital waveform

Sensor design matters. A passive variable-reluctance sensor and an active Hall-effect sensor do not use the same test procedure.

Step 12: Inspect the Tone Ring or Encoder

Wheel-speed sensors commonly read a toothed ring or magnetic encoder.

Inspect for:

Cracked tone ring
Missing teeth
Rust expansion
Debris
Damaged magnetic encoder
Excessive wheel-bearing play
Incorrect bearing
Bearing installed backward
Sensor contact with the encoder

A wheel bearing with a one-sided magnetic encoder must be installed in the correct direction. Putting the encoder on the wrong side is an impressively efficient way to install a new part that cannot be read.

Diagnosing the Sensor A Circuit and Network

Step 13: Inspect Wiring and Connectors

Check for:

Open circuit
Short to ground
Short to voltage
High resistance
Loose terminal tension
Corroded pins
Water intrusion
Chafed insulation
Heat damage
Collision damage
Poor previous repairs

Move the harness while monitoring live data or waveform output to locate intermittent faults.

Always use appropriate terminal tools when checking connector tension. Forcing an oversized test probe into a terminal can create the loose connection being diagnosed.

Step 14: Test CAN Communication

If Sensor A information is transmitted between modules, inspect the controller network.

Check for:

U-codes
Missing modules
Incorrect CAN high or CAN low voltage
Network resistance where appropriate
Shorted communication circuits
Intermittent connectors
Water-damaged modules
Aftermarket equipment attached to network wiring

An oscilloscope may be required to identify intermittent waveform distortion.

Do not splice test lights or powered probes into a CAN circuit.

Step 15: Verify Module Configuration

After PCM, ABS or chassis-module replacement, confirm:

Correct module part number
Correct VIN
Correct software calibration
Correct ABS options
Correct stability-control options
Correct drivetrain configuration
Correct tire-size configuration
Correct rough-road sensor assignment
Required programming completed

An incorrectly configured PCM may expect a Sensor A signal from hardware the vehicle does not use.

A used module may contain option data from a completely different vehicle. It bolts in nicely, communicates politely and remains profoundly confused.

Step 16: Complete Required Calibration

Depending on the application, repairs may require:

Rough-road sensor initialization
Accelerometer calibration
Steering-angle calibration
Yaw-rate calibration
ABS module setup
Wheel-speed sensor relearn
Tire-size programming
PCM setup

Follow the exact manufacturer procedure.

Calibration should occur only after the sensor, wiring, communication and module configuration have been verified.

Step 17: Check Crankshaft Monitoring if Necessary

Because rough-road information supports misfire monitoring, check the crankshaft system when related codes or abnormal data are present.

Inspect:

Crankshaft position sensor
Sensor wiring
Signal waveform
Reluctor wheel
Variation calibration

Relevant guides include:

Do not replace the crankshaft sensor solely because P0318 is stored.

Step 18: Determine Whether an Actual Misfire Exists

If P0318 appears with a misfire code, monitor:

Individual-cylinder misfire counters
Mode $06 data
Fuel trims
Ignition operation
Injector operation
Engine compression
Exhaust rhythm

A combustion misfire that occurs consistently on smooth roads requires normal engine diagnosis.

A misfire count that appears only during rough-road events may indicate invalid or missing Sensor A information.

Step 19: Clear P0318 and Verify the Repair

After correcting the confirmed fault:

Clear PCM and chassis-module codes.
Complete required programming or calibration.
Verify communication with all modules.
Monitor Sensor A live data.
Confirm smooth wheel-speed signals.
Drive on a smooth road.
Cross a controlled uneven surface when safe.
Monitor misfire counters.
Complete the required drive cycle.
Rescan every module.

The repair is confirmed when Sensor A data remains valid and P0318 does not return.

Common P0318 Repairs and Costs

Repair	Approximate installed cost
Repair connector or minor wiring	$100–$500
Replace wheel-speed sensor	$150–$500
Replace wheel bearing or encoder hub	$300–$900
Replace dedicated rough-road sensor	$200–$800
Complete sensor calibration	$100–$400
Repair CAN wiring	$200–$1,500+
Program or configure PCM	$150–$500
Program or configure ABS module	$200–$700
Replace ABS control module	$800–$2,500+
Replace crankshaft position sensor	$150–$600

P0318 may require only a wiring repair, module setup or sensor calibration rather than component replacement.

Common P0318 Diagnostic Mistakes

Assuming Sensor A Is a Wheel-Speed Sensor

Sensor A may be a dedicated accelerometer, calculated ABS value or network message.

Replacing Sensor A Without Testing Its Circuit

Verify power, ground, signal, mounting and communication before replacement.

Ignoring ABS Module Codes

The PCM may store P0318 because another module stopped supplying valid data.

Using the Wrong Electrical Test

Active, passive, analog, digital and network-based sensors require different testing methods.

Ignoring Sensor Orientation

An accelerometer mounted incorrectly may produce an implausible signal despite being electrically functional.

Replacing the PCM First

PCM failure is rare compared with wiring, sensor, communication and configuration problems.

Ignoring Programming After Module Replacement

A replacement PCM or ABS module may require programming, option configuration and calibration.

Treating P0318 as an Engine Misfire

P0318 affects rough-road data used during misfire validation. It does not prove combustion is failing.

Clearing Only the PCM

Related codes may remain stored in the ABS or chassis-control modules.

P0318 Frequently Asked Questions

What does P0318 mean?

P0318 means the PCM detected a problem with the Rough Road Sensor A signal or circuit.

What is Rough Road Sensor A?

It is the manufacturer-designated source of rough-road data. It may be a dedicated sensor, ABS-calculated value or network message.

Is Sensor A the left-front wheel-speed sensor?

Not necessarily. The A designation is manufacturer-specific.

Can a bad ABS sensor cause P0318?

Yes. If the vehicle calculates rough-road conditions using wheel-speed data, an ABS sensor fault may cause P0318.

Can a wheel bearing cause P0318?

Yes. A damaged or incorrectly installed magnetic encoder can disrupt wheel-speed information.

Does P0318 mean the engine is misfiring?

No. It means the rough-road signal used to validate misfire data is faulty.

Can P0318 turn on the ABS light?

It may appear with an ABS warning when the underlying fault affects the ABS system.

Can PCM programming cause P0318?

Yes. Incorrect configuration may cause the PCM to expect a signal from the wrong sensor or module.

Can an ABS module replacement cause P0318?

Yes. The replacement module may require programming, configuration and calibration.

Can different tire sizes cause P0318?

Large rolling-diameter differences or incorrect tire-size programming can affect wheel-speed calculations on some vehicles.

Can I drive with P0318?

Usually for a short distance if braking, ABS, stability control and engine operation remain normal. Drive cautiously and diagnose the fault promptly.

Will P0318 clear itself?

An intermittent code may become historical if the signal returns, but it can remain stored until cleared or enough successful drive cycles occur.

Related OBD-II Codes

P0317 — Rough Road Hardware Not Present
P0318 — Rough Road Sensor A Signal Circuit
P0319 — Rough Road Sensor B Signal Circuit
P0315 — Crankshaft Position Variation Not Learned
P0335 — Crankshaft Position Sensor A Circuit
P0300 — Random or Multiple-Cylinder Misfire
C0035–C0051 — Wheel-Speed Sensor Codes
U-codes — Module Communication Faults

Explore the Pro Street OBD-II Code Libraries

Use the Pro Street cornerstone pages to find additional diagnostic trouble codes:

P0318 means the PCM detected an invalid, missing or implausible Rough Road Sensor A signal.

Begin by scanning every control module and identifying what Sensor A represents on the specific vehicle. Test the physical sensor or ABS-derived data, inspect wiring and communication, and verify module configuration and calibration.

Do not replace a wheel-speed sensor merely because the code contains the words “rough road.” The vehicle may be waiting for an accelerometer, an ABS calculation or a network message—which is the automotive equivalent of three departments insisting someone else owns the ticket.

P0318 Code: Rough Road Sensor “A” Signal Circuit