P0886 Code: TCM Power Relay Control Circuit Low

What the P0886 code means

The transmission control module (TCM) needs a steady, clean power supply to do its job. Some vehicles feed it through a relay that the module itself switches on, and others feed it straight from the fuse box. Either way, the module keeps an eye on its own supply voltage.

The module watches the control circuit through its own driver transistor. The P0886 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. Those are the most common causes by far.

When the supply voltage is low or unstable, the transmission shifts erratically or drops into limp mode, and you can end up with solenoid codes that are really caused by this power problem and not by bad solenoids. Check the battery, the alternator, the fuses and the grounds first.

Here is a good way to confirm the fault. Unplug the component with the key on and watch what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is fine and the component itself is pulling the signal to ground. If nothing changes, hunt for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0886 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 P0886 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 P0886 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 P0886 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

The power relay for the transmission computer is usually easy to find once you know which fuse box holds it, so start there before pulling any harness apart.

P0886 on Chrysler

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

P0886 on Ford

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

Frequently asked questions about P0886