What it means
The TCM power relay reports a sense circuit range/performance condition. TCM supply control is impaired.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The TCM power relay sense circuit reports the relay's electrical output so the TCM can verify its power supply. P0889 sets when the feedback is outside its expected range or does not behave as expected, which can result from drifting relay contact resistance, an unstable feedback signal, or a degraded sensing element.
Common causes
Most likely first.
- Contact resistance drifted
- Feedback voltage drifted
- Sensor element aged beyond calibration window
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
- Save freeze-frame data and compare live relay command and sense readings to find when the feedback moves outside its expected range.
- Inspect the relay and feedback-circuit connectors for corrosion, loose fit, heat damage, or pins that have moved back.
- Check the feedback wire for damage and measure continuity through the circuit against the manufacturer's specification.
- Monitor the sense signal as the relay is commanded and compare its behavior with the manufacturer's specification.
- If wiring and connections are sound, test relay contact behavior and the TCM sense input for drift using the manufacturer's procedure.
Common fixes
- Clean and secure corroded or loose feedback-circuit connections.
- Repair a damaged or high-resistance sense wire.
- Replace a relay with contacts whose resistance is outside the manufacturer's specification.
- Replace or repair the sensing component or TCM input only if testing confirms it is out of calibration.
Can I keep driving?
If the transmission shifts normally, keep trips short and watch for worsening behavior. Avoid driving if shifts become harsh or delayed or limp mode begins, since inconsistent relay feedback can disrupt transmission control.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.