What Does P1318 Mean?
P1318 indicates that the ABS rough road signal line is stuck high or transmitting an erroneous high-voltage signal to the powertrain control module. The ABS module sends wheel speed variation data to the PCM to help distinguish road-surface-induced crankshaft speed fluctuations from actual engine misfires. A stuck-high signal corrupts this compensation.
Common Causes
30%
Short to voltage in the rough road signal wire between ABS and PCM
25%
ABS control module rough road output circuit failure
20%
Damaged wiring harness in the ABS-to-PCM communication link
15%
Corroded connector at the ABS module or PCM
10%
PCM rough road input circuit failure
Diagnostic Steps
1
Check for ABS-related DTCs that may indicate a broader ABS module issue.
2
Inspect the wiring between the ABS module and PCM for the rough road signal line — look for chafing, shorts, or water damage.
3
Measure the rough road signal voltage at the PCM connector — it should vary with vehicle speed and road conditions, not be stuck high.
4
Disconnect the ABS module connector and check if the signal line voltage drops, isolating whether the fault is in the ABS module or wiring.
5
Verify connector pin integrity at both the ABS module and PCM ends.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
P1318 indicates that the ABS rough road signal line is stuck high or transmitting an erroneous high-voltage signal to the powertrain control module. The ABS module sends wheel speed variation data to the PCM to help distinguish road-surface-induced crankshaft speed fluctuations from actual engine mi...
The most common cause of P1318 (ABS Rough Road Line High Fault) is: Short to voltage in the rough road signal wire between ABS and PCM
Typical repair costs for P1318 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This fault affects misfire detection accuracy — the PCM may either miss real misfires or flag false ones on rough roads. ABS braking function itself is typically unaffected. No immediate safety hazard but repair is recommended.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1318 to identify the root cause.
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Quick Info
Category
Powertrain
System
ABS / Misfire Detection Interface
Difficulty
Type
Manufacturer
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