Open Power To Ground VCRM
The ECU detects a broken or disconnected wire in the Variable Camshaft Rocker Module (VCRM) power circuit, like a lamp with a loose power cord that won't turn on. The engine can't properly control variable valve timing because it can't send power to the solenoid.
The ECU monitors the voltage supply to the VCRM solenoid circuit and detects an open circuit (break in the power path to ground). When voltage cannot reach the solenoid or return properly to ground, the ECU recognizes the fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| VCRM Supply Voltage | 12-14 volts with solenoid engaged | 0 volts or no voltage drop when command active |
| Ground Circuit Resistance | Less than 0.5 ohms | Open circuit or infinite resistance detected |
Code P1491 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1491 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.