TCM Power Relay Sense Circuit High
The transmission control module's power relay isn't receiving the correct voltage signal it expects, like a doorbell that's stuck reporting the button is being pressed when it isn't. This prevents the TCM from properly monitoring its own power supply.
The TCM monitors the voltage feedback from its power relay sense circuit to verify the relay is functioning and supplying adequate power. The ECU compares this signal against expected voltage thresholds; when the voltage reads abnormally high, it indicates a wiring fault, relay failure, or PCM communication issue.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| TCM Power Relay Sense Voltage | 0.5–4.5V (relay inactive to active) | >4.5V or stuck high condition |
| Relay Circuit Resistance | <5 ohms when engaged | Open circuit or >10 ohms |
Code P0891 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, P0891 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.