Transmission Control System MIL Request Circuit Low
The transmission control module is trying to turn on the check engine light, but the signal wire to do so is reading too low in voltage. It's like a light switch that's broken and won't send the "on" command properly.
The ECM monitors the MIL request circuit voltage from the transmission control module to verify the ability to trigger the malfunction indicator lamp. When this circuit voltage drops below the minimum threshold, it indicates a wiring fault, short to ground, or TCM communication failure. The ECM expects a high voltage signal; a low voltage indicates an open circuit or short condition.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| MIL Request Circuit Voltage | Above 10 volts | Below 5 volts or shorted to ground |
| Circuit Resistance | Less than 5 ohms | Greater than 10 ohms or open circuit |
Code P0898 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, P0898 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.