P2608 indicates that the PCM has detected a voltage higher than expected in the intake air heater B circuit. The intake air heater is used to warm incoming air during cold starts to improve combustion and reduce emissions.
The heater coil or resistive element has shorted internally, causing excessive voltage draw that the PCM interprets as a high‑circuit condition.
Chafed, pinched, or corroded wires can create a short to battery voltage, raising the circuit voltage seen by the PCM.
A fuse that has opened or a relay that sticks closed can alter the voltage supplied to the heater, triggering the high‑voltage code.
Poor grounding or loose terminals at the heater, PCM, or splice points can cause voltage spikes or intermittent high readings.
Although sometimes suggested, the PCM rarely causes this code; it should be considered only after all wiring, heater, fuse, and relay checks are normal.
No. The PCM is rarely the cause of this code. Most P2608 faults are due to a failed heater element, wiring short, or fuse/relay issue. Replace the PCM only after those components have been verified good.
You can usually drive, but you may experience hard starts or rough idle in cold weather until the heater circuit is repaired. Prolonged operation with a faulty heater may increase emissions during cold starts.
No. The intake air heater warms the incoming air charge, whereas glow plugs heat the combustion chamber directly in diesel engines. They are separate systems.