01 Why Spare Parts Shops Are One of the Most Profitable Busine… • 02 Signs Your Car Needs an Oil Change and Oil Top-Up: Warnings… • 03 How Bad Is It to Drive with a Leaking Head Gasket? • 04 How to Improve Fuel Efficiency in Cars: Tips and Techniques • 05 B0053: Deployment Commanded with Loop Malfunctions Present • 06 Battery Troubleshooting: When to Replace or Recharge • 07 What Happens If You Shift to Reverse While Driving at High … • 08 The Sneaky Mechanical Piece That Increases Fuel Consumption… • 09 The Meaning of Major Dashboard Light: A Comprehensive Guide • 10 This Everyday Habit Might Be Slowly Killing Your Transmissi… •

DTC codes / P08xx · Transmission / P0891

P0891TCM Power Relay Sense Circuit High

P0891 means the transmission control module (TCM) has detected an abnormally high voltage on the sense circuit that monitors the power relay feeding the TCM and its solenoids. The TCM expects this sense line to sit at a specific voltage when the relay is commanded on, and a reading above the calibrated threshold tells it the relay circuit is not behaving as designed.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Illuminated check engine light or transmission warning lamp, often with no other symptoms besides the warning light
  • Transmission stuck in a default or limp mode with harsh or delayed shifts
  • No power feed to the transmission solenoids, causing the vehicle to stay in one gear or fail to engage drive
  • Intermittent loss of transmission function that clears after the ignition is cycled
  • Other modules logging low-voltage or communication codes because the TCM lost its power feed
  • A no-crank or no-start condition on vehicles where the same relay also feeds the TCM at key-on

Common causes, most likely first

  1. A failing TCM power relay whose contacts have burned or welded, holding the sense line high
  2. Corroded, loose, or backed-out terminals in the relay socket or TCM harness connector
  3. A short to voltage on the relay sense wire where it rubs through against another power circuit
  4. A faulty TCM with an internal driver or sense-circuit fault reading the line incorrectly
  5. Water intrusion into the relay box or TCM connector causing conductive corrosion paths
  6. A blown or improperly rated fuse in the relay feed circuit altering the sense voltage
  7. Poor ground at the TCM or relay mounting point that shifts the sense reference voltage

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data for P0891 plus any companion codes before touching anything
  2. Locate the TCM power relay in the underhood or interior fuse box and swap it with an identical known-good relay to see if the code changes
  3. Inspect the relay socket and TCM connector pins for corrosion, heat damage, and loose terminals, then clean and reseat them
  4. Measure voltage on the relay sense circuit at the TCM connector with the key on and compare it to the manufacturer's expected range
  5. Wiggle-test the harness while watching live sense-circuit data to expose an intermittent short to voltage
  6. Check the TCM ground and relay feed fuses with a voltage drop test rather than a simple continuity check
  7. If wiring and relay test good, substitute a known-good TCM or perform the manufacturer's relearn procedure before condemning the module

Why the relay is not always the culprit

  • A high sense voltage often comes from a short to voltage on the sense wire rather than a failed relay, so replacing the relay first frequently does not clear the code.
  • Technicians commonly overlook the TCM ground; a lifted ground raises the reference voltage on the sense line and mimics a relay fault.
  • This code can set intermittently from water intrusion in the relay box, so a code that clears after a dry spell still needs the connector inspected.
  • On some platforms the TCM power relay also feeds other modules, so a single failed relay can set several unrelated communication codes alongside P0891.
  • A scan tool that only reads generic OBD-II data may not show the TCM sense voltage, so manufacturer-level live data is needed to confirm the circuit behavior.

Can I keep driving with P0891?

The vehicle may enter limp mode or lose transmission function while driving, so limit travel to a short distance to a safe repair location and avoid highway speeds or towing until the circuit is diagnosed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage