P0318
Rough Road Sensor A Signal CircuitP0318 is a generic OBD-II powertrain diagnostic trouble code: Rough Road Sensor A Signal Circuit. It is logged by the engine control unit when the misfire monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0318 means
P0318 — "Rough Road Sensor \"A\" Signal Circuit" — is set when the PCM detects an electrical fault in the signal circuit of the primary (channel A) rough road sensor. The rough road detection system prevents the misfire monitor from flagging wheel-hop-induced crankshaft velocity variations as engine misfires. Depending on the platform, the sensor may be a dedicated accelerometer, or the signal may be derived from ABS wheel speed sensors via the Electronic Brake Control Module (EBCM).
Unlike P0317 (hardware not present), P0318 means the hardware exists but its signal circuit has a measurable electrical fault — such as an out-of-range voltage, open circuit, or short. The PCM monitors the sensor output during the drive cycle; if the signal falls outside expected parameters or is absent when the vehicle is moving, the code is stored. The MIL typically does not illuminate on all platforms for this code, though related warning lights such as traction control or ABS may appear.
Diagnosis requires verifying the sensor supply voltage and signal output against manufacturer specifications. The EBCM should be checked for its own fault codes on platforms where it acts as the rough road data source, since an EBCM fault can manifest as a P0318 on the PCM side. Addressing wiring issues before replacing sensors is always the recommended first step.
Common causes
Most-frequently reported root causes when P0318 is logged.
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1
Open circuit or broken wire in the rough road sensor \"A\" signal line between the sensor and PCM.
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2
Short to ground or short to voltage on the sensor signal circuit.
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3
Corroded, damaged, or loosely seated electrical connector at the rough road sensor or EBCM.
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4
Faulty rough road accelerometer sensor with degraded internal signal output.
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5
EBCM malfunction causing invalid or absent rough road data on systems using ABS-derived input.
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6
Damaged wiring harness routed near heat sources or sharp edges causing intermittent opens.
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7
PCM input circuit fault preventing correct reading of the sensor signal.
Symptoms drivers notice
How to diagnose P0318
A typical diagnostic flow when this code is present.
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1
Retrieve all stored codes with a scan tool; note any ABS, traction control, or misfire codes alongside P0318.
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2
Inspect the rough road sensor \"A\" connector and wiring harness for corrosion, damage, or loose pins.
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3
Measure supply voltage and ground reference at the sensor connector with the ignition on; compare against manufacturer specifications.
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4
Use a digital multimeter to test signal circuit continuity and check for shorts between signal, power, and ground wires.
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5
Monitor the rough road sensor \"A\" PID on a live data scan tool while driving over varied road surfaces to confirm signal presence and range.
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6
If the platform uses the EBCM as the rough road data source, retrieve EBCM codes and verify EBCM communication health.
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7
Replace the rough road sensor only after wiring and connector integrity are confirmed — retest after replacement to verify the fault is cleared.
Related powertrain codes
Frequently asked questions
What is the difference between P0317 and P0318?
P0317 means the PCM cannot find rough road hardware at all — it is absent or unconfigured. P0318 means the hardware (channel A sensor) exists and is expected, but its electrical signal circuit has a measurable fault such as an open, short, or out-of-range voltage.
Why does P0318 sometimes not turn on the Check Engine Light?
Some manufacturers calibrate the PCM to store P0318 as an informational or type-B code that requires two consecutive failed drive cycles before illuminating the MIL. The ABS or traction control warning may appear instead if the fault originates in the EBCM.
Can a bad ABS module cause P0318?
Yes. On vehicles where the rough road signal is derived from ABS wheel speed data via the EBCM rather than a standalone accelerometer, an EBCM fault or communication loss will cause the PCM to see an invalid channel A signal and set P0318.
Is it safe to drive with P0318?
Short-term driving is generally safe, but without a functional rough road signal the misfire monitor may generate false misfire codes on uneven surfaces, complicating diagnosis. It is advisable to repair the fault promptly to keep the misfire monitor reliable.
Disabling P0318 in software
RaceTune can permanently disable P0318 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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