P0890 Code: TCM Power Relay Sense Circuit Low

What the P0890 code means

The transmission control module (TCM) needs a steady power supply. Some vehicles feed it through a relay that the module itself controls, and others feed it directly from the fuse box. The module watches its supply voltage at all times.

The module monitors the control circuit through its own driver transistor. The P0890 code is set when that circuit shows low voltage, which usually means a short to ground or a loss of power. Before you replace any part, check the fuse, relay, connector and wiring, since those 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.

To confirm the fault, unplug the component with the key on and watch the reading or the code. If the value jumps to the opposite extreme, the wiring is good and the component is the one pulling the signal to ground. If nothing changes, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0890 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 P0890 code

1. Control wire shorted to ground. The component can stay switched on all the time, or the computer cuts the output to protect itself.
2. Interrupted power supply. A blown fuse, a faulty relay or a broken wire.
3. Shorted component. Its resistance is far lower than the specification.
4. Connector with moisture. Water creates a path to ground.

How to diagnose the P0890 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 P0890 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.
• Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

If the connector looks wet or the terminals are green, dry it, clean it and protect it before you do anything else. Moisture alone can create the short that sets this code.

P0890 on Chrysler

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

P0890 on Ford

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

Frequently asked questions about P0890