P2078 indicates the powertrain control module (PCM) has detected a voltage signal from the intake manifold tuning (IMT) valve position sensor on bank 1 that is higher than the expected range. This sensor monitors the position of the variable-length intake manifold runner control valve, which optimizes engine torque across the RPM range. A high circuit voltage typically points to an open circuit, sensor failure, or wiring issue rather than a mechanical valve problem.
Internal open circuit or short to voltage within the sensor causes the PCM to read a continuously high signal.
A broken wire or disconnected terminal in the signal circuit prevents the sensor voltage from being pulled down to the normal range.
Corrosion, bent pins, or loose terminals at the sensor connector create high resistance or an open circuit.
The sensor signal wire may be shorted to a power source, pulling the voltage above the maximum threshold.
If the runner control valve sticks, the position sensor may report an out-of-range high voltage due to inability to reach commanded positions.
Rare; an internal PCM driver or input circuit failure can falsely set the code after all external wiring and sensor tests pass.
Not necessarily. The code indicates a high voltage in the position sensor circuit, which is often caused by a wiring issue or failed sensor rather than a mechanical valve failure.
The vehicle will likely run, but you may notice reduced low-end torque, rough idle, and poorer fuel economy. Extended driving is not recommended until repaired.
No. PCM failure is a rare cause; the fault is almost always in the sensor, its wiring, or the connector. Replacing the PCM without thorough circuit testing typically does not fix the code.
Clearing the code only turns off the check engine light temporarily. If the underlying circuit fault remains, the code will return once the PCM runs its monitor.