P2491 indicates the Powertrain Control Module (PCM) sees a high voltage on the EGR cooler bypass control circuit for Bank 2, meaning the circuit is stuck above the expected voltage level. This is typically caused by a short to power, an open ground, or a failure of the bypass valve itself. The code often results in a check‑engine light and may affect idle quality and emissions.
The valve’s internal solenoid may short to battery voltage or fail mechanically, causing the circuit to read high.
A chafed wire, corroded terminal, or broken connector can create a short‑to‑power condition, pulling the circuit voltage high.
If the fuse for the valve circuit is open or the relay is stuck, the voltage reading can be abnormal.
An inadequate ground can prevent the PCM from pulling the circuit low, leaving it at a high voltage state.
Rarely, the PCM’s output transistor for the bypass valve may fail, but this is the least common cause and should be verified after other components are checked.
No. The PCM’s driver rarely fails; most cases are caused by the bypass valve itself, wiring problems, or a blown fuse. PCM replacement should be considered only after the more common causes are eliminated.
You can drive, but the engine may run roughly and emissions could increase. It’s advisable to address the issue promptly to avoid potential catalytic converter or emissions test failures.
If the valve is faulty, replacing it usually resolves the code. However, you should also inspect the wiring and connectors for damage, as an underlying short can cause the new valve to fail.
An intermittent wiring issue—such as a loose connector or a wire that rubs under engine movement—can cause the code to recur. A thorough visual inspection and, if needed, a wiggle test can reveal these intermittent faults.