P0889Generic code

P0889 Code: TCM Power Relay Sense Circuit Range/Performance

The P0889 code means the power or ground feeding the transmission computer power relay circuit is outside the expected range. It can send the transmission into limp mode or cause erratic shifting. Check the fuse, relay and grounds before you condemn any component.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$10 to $400
Difficulty
Medium
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0889 code means

The transmission control module (TCM) needs a steady power supply. Some vehicles feed it through a relay that the module controls, and others feed it directly from the fuse box. The module keeps checking its own supply voltage.

The module watches the control circuit through its own driver transistor. The P0889 code is set when it detects a fault in the power or ground of that circuit, in this case a reading that falls outside the expected range. Before you replace any part, check the fuse, relay, connector and wiring. They are the most common causes.

When the voltage is low or unstable, the transmission shifts erratically or goes into limp mode, and solenoid codes can appear even though the solenoids are good. Check the battery, the alternator, the fuses and the grounds first.

Measure the voltage at the connector with the component working. A big drop compared with the battery points to a power feed or a ground with too much resistance. Measure the voltage drop on the ground wire too. It should be under 0.2 volts under load.

P0889 code symptoms

  • Check engine light or another warning light on.
  • Transmission in limp mode or shifting erratically.
  • Erratic shifts, with gears that come at the wrong time or not at all.
  • Limp mode, usually stuck in a single gear.
  • Several transmission codes stored at the same time.

Likely causes of the P0889 code

  1. Blown fuse or relay. The fuse may be open, or the relay contacts may be worn.
  2. Loose or corroded ground. It adds resistance to the circuit.
  3. Damaged power wire. Heat or rubbing wears through the insulation.

How to diagnose the P0889 code step by step

  1. Command the component with the scan tool and check whether it responds.
  2. Check the fuse and the relay. Measure voltage on both sides of the fuse, and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when the component is commanded.
  4. Measure the resistance of the component and compare it with the manual. Also check its insulation to ground.
  5. Check the control wire. Confirm continuity all the way to the computer and make sure there is no short.
  6. Measure battery voltage and charging voltage.
  7. Measure the voltage drop across the module grounds. It should be under 0.2 volts.

How to fix the P0889 code

  • Repair the connector, the wiring or the power supply feed.
  • Replace the transmission computer power relay or its supply component if it does not respond even with correct power and control signals.
  • Clear the codes and road test the vehicle to verify the repair.

Technical reference data

  • Supply voltage: battery voltage, which is 13.5 to 14.7 volts with the engine running.
  • Voltage drop across a ground under load: below 0.2 volts.
  • Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

A reading that is out of range, and not completely missing, often means a connection that is weak but not fully broken. Wiggle test the harness while watching live data to catch it.

P0889 on Chrysler

On many Chrysler vehicles the transmission relay sits in the fuse box in the engine compartment.

P0889 on Ford

On many Ford vehicles the transmission relay sits in the fuse box in the engine compartment.

Frequently asked questions about P0889

Can I drive with a P0889 code?
Yes, but with caution. The transmission may shift erratically or enter limp mode, so keep trips short and have it checked soon.
What does the transmission computer power supply do?
The transmission computer needs a steady supply to work. Some vehicles feed it through a relay the module controls, and others feed it directly from the fuse box. The module monitors that supply voltage and sets a code when it looks wrong.
Do I always have to replace the part?
No. Check the fuses, relays, connectors, wiring and grounds first. They are the usual causes and cost much less than a new component.
How much does it cost to fix P0889?
As a rough guide, between $10 and $400. A fuse or a ground cleanup is cheap, while a wiring repair or a new relay costs more.
What does the P0889 code mean?
The P0889 code is a generic OBD2 code that means the power or ground of the transmission computer power relay circuit is outside the expected range. That points to a fuse, relay, wire or ground problem.
Will a P0889 code clear itself?
Only if the cause was a one-time event. A worn relay or a poor ground will bring the code back and keep the light on.
What is the most common cause of P0889?
A blown fuse, a worn relay, a loose or corroded ground, or a power wire damaged by heat or rubbing.

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