P0891: TCM Power Relay Sense Circuit High

What it means

The TCM detects a voltage level above the expected range in the power relay sense circuit.

At a glance

• Usually lights the check-engine light

How it works

The TCM power relay supplies power to the transmission control module, and the sense circuit reports whether that supply is present. The TCM sets P0891 when the sensed voltage is higher than its expected range, which can happen if the sense wire is shorted to voltage or the relay remains closed.

Common causes

Most likely first.

1. Short to voltage in the sense circuit
2. Power relay stuck closed
3. Faulty relay or TCM

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Record freeze-frame data and check for related power-supply or transmission codes to see when the relay sense voltage went high.
2. With the vehicle safely parked, inspect the TCM power relay and its connector for damage, corrosion, or signs that the relay is stuck closed.
3. Check the sense-circuit wiring for a short to a powered wire, pinched insulation, or a poor connection.
4. Use a scan tool or meter to compare relay command and sense-circuit readings with the manufacturer's specification.
5. If the wiring and relay test correctly, check the TCM power and ground connections, then assess the TCM circuit.

Common fixes

• Repair a damaged sense-circuit wire or connector that is shorted to voltage.
• Clean or secure a poor relay or TCM connector.
• Replace a power relay that is stuck closed or fails testing.
• Repair the TCM circuit or replace the TCM if testing confirms an internal fault.

Can I keep driving?

Avoid long trips or hard acceleration if shifts are harsh, delayed, or slipping, since abnormal shifting can worsen transmission damage. If the vehicle is stuck in one gear or loses drive, stop in a safe place and arrange assistance.