What Does P3491 Mean?
The PCM detects abnormally low voltage or short to ground in cylinder 12's intake valve control circuit. Excessive current flow or ground fault is preventing proper valve control system operation.
Common Causes
40%
Short to ground in wiring harness between PCM and intake valve control solenoid
30%
Internal short to ground within intake valve control solenoid coil
15%
Chafed or pinched wire contacting engine block or chassis ground
10%
Moisture or oil intrusion in connector creating low resistance path to ground
5%
Failed PCM driver circuit with internal short
Diagnostic Steps
1
Step 1: Disconnect intake valve control solenoid and measure resistance from control wire terminal to ground; should read infinite resistance
2
Step 2: Measure solenoid coil resistance to ground; low resistance indicates internal short requiring solenoid replacement
3
Step 3: Inspect entire wiring harness for damage, especially near heat sources, moving parts, and sharp edges
4
Step 4: Check for fluid contamination in connectors that could create conductive paths; clean and seal if necessary
5
Step 5: Monitor current draw on circuit with amp clamp during operation; excessive current confirms short circuit
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The PCM detects abnormally low voltage or short to ground in cylinder 12's intake valve control circuit. Excessive current flow or ground fault is preventing proper valve control system operation.
The most common cause of P3491 (Cylinder 12 Deactivation/Intake Valve Control Circuit Low) is: Short to ground in wiring harness between PCM and intake valve control solenoid
Typical repair costs for P3491 range from $150 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle can be driven but cylinder deactivation will not function. Short circuit condition may cause PCM damage if not repaired; address promptly to prevent cascading electrical failures.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P3491 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cylinder Deactivation/Variable Valve Timing System
Difficulty
Type
Generic (SAE)
Recommended Tools
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