P0885 Transmission Control Module (TCM) Power Relay Control Circuit/Open

The P0885 trouble code is an OBD-II diagnostic trouble code related to the Transmission Control Module (TCM) power relay control circuit.

P0885 – Transmission Control Module (TCM) Power Relay Control Circuit/Open

This code means that the TCM has detected an open or interrupted electrical circuit in the control circuit used to operate the TCM power relay.

The TCM power relay supplies electrical power to the transmission control system. The relay is controlled through an electrical circuit that allows the TCM or another control module to turn the relay on and off.

If the control circuit is open, disconnected or unable to complete the required electrical path, the relay may not activate and the TCM may not receive the required power.

Possible causes include:

• Open relay control wire

• Broken wiring

• Disconnected connector

• Faulty TCM power relay

• Faulty relay coil

• Loose relay terminal

• Corroded relay socket

• Damaged fuse or fuse box

• Poor electrical connection

• Faulty ignition power supply

• Poor TCM ground

• Damaged TCM connector

• Water intrusion

• Incorrect relay

• Faulty TCM

• Previous wiring repair

The exact circuit arrangement varies by vehicle manufacturer.

What Does P0885 Mean?

P0885 – Transmission Control Module (TCM) Power Relay Control Circuit/Open

The TCM power relay normally receives a control signal that causes it to activate.

A simplified system can be represented as:

Battery → Fuse → TCM Power Relay → TCM / Transmission System

The relay also has a control circuit:

TCM → Relay Control Circuit → TCM Power Relay

When the TCM needs to power the transmission control system, it commands the relay.

If the control circuit is interrupted, the relay may remain OFF.

For example:

TCM commands relay → Control circuit is open → Relay does not activate → TCM power is unavailable → P0885

What Does “Circuit/Open” Mean?

The word “Open” means that the electrical circuit is interrupted and the expected current cannot flow through the control circuit.

An open circuit can be caused by:

• Broken wire

• Disconnected connector

• Loose terminal

• Corroded terminal

• Failed relay coil

• Damaged relay socket

• Missing power or ground

• Internal module fault

This is different from a “Low” code such as P0886.

P0885 → Open/interrupted circuit

P0886 → Control circuit voltage/signal low

What Is the TCM Power Relay?

The TCM power relay is an electrically controlled switch that supplies power to the transmission control system.

A simplified operating sequence is:

Ignition ON → TCM commands relay → Relay activates → TCM/transmission system receives power

Depending on the vehicle, the relay may supply power to:

• TCM

• Transmission solenoids

• Mechatronic unit

• Sensors

• Actuators

If the relay cannot be activated because its control circuit is open, these systems may lose their required power.

Symptoms of P0885

Because the TCM power relay may not activate, P0885 can produce significant transmission symptoms.

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Transmission warning message

• Transmission stuck in one gear

• Limp mode

• No gear selection

• Delayed shifting

• Harsh shifting

• Loss of reverse

• Loss of forward gears

• Vehicle will not move

• TCM communication failure

• Incorrect gear indication

• Intermittent transmission operation

In severe cases, the vehicle may crank and start but the transmission may not engage.

Common Causes of P0885

Broken relay control wire

A broken conductor can completely interrupt the relay control circuit.

Disconnected connector

A connector that is not fully seated can leave the control circuit open.

Corroded connector terminal

Corrosion can prevent the electrical connection from being completed.

Faulty relay

A failed relay coil can behave like an open circuit.

Damaged relay socket

The relay socket may have:

• Broken terminals

• Loose pins

• Corrosion

• Burn damage

Faulty fuse or power supply

Although P0885 concerns the control circuit, missing relay power can prevent the relay from operating.

Faulty ignition circuit

Some systems depend on ignition-switched power for relay operation.

Poor ground

Depending on the circuit design, a missing ground can prevent the relay from activating.

Water intrusion

Moisture can cause corrosion and open circuits around the relay, fuse box or TCM.

Incorrect relay

The wrong relay may not have the required internal electrical configuration.

Faulty TCM

The TCM may fail to provide the required relay control signal.

The TCM should only be considered after the wiring and relay circuit have been properly tested.

Is P0885 a Serious Transmission Problem?

P0885 can be a serious fault.

The code concerns the circuit responsible for controlling the TCM power relay.

If the relay cannot activate, the transmission control system may lose power.

This can cause:

• Loss of gear control

• Limp mode

• No shifting

• Loss of drive

• TCM communication problems

However, P0885 does not automatically indicate internal transmission damage.

A broken wire, disconnected connector or failed relay can cause the code.

Can You Drive With P0885?

Driving with P0885 is generally not recommended if the transmission is already showing symptoms.

If the vehicle operates normally and the code is stored without symptoms, a short trip to a repair facility may be possible.

Do not continue driving if:

• The transmission is stuck in one gear

• The vehicle cannot select gears

• Reverse is unavailable

• Limp mode is active

• Gear selection is unpredictable

• The vehicle loses drive

An open control circuit can cause the TCM power relay to stop functioning completely.

P0885 vs. P0886

These codes concern the same general relay control system but describe different electrical conditions.

P0885 – TCM Power Relay Control Circuit/Open

The control circuit is interrupted or open.

P0886 – TCM Power Relay Control Circuit Low

The control circuit signal is lower than expected.

In simple terms:

P0885 → Circuit interrupted

P0886 → Circuit signal too low

P0885 vs. P0887

P0887 – TCM Power Relay Control Circuit High

The control circuit voltage or signal is higher than expected.

P0885 – TCM Power Relay Control Circuit/Open

The control circuit is interrupted.

Therefore:

P0885 → Open

P0886 → Low

P0887 → High

P0885 vs. P0888

These codes concern different parts of the relay system.

P0885 concerns the control circuit used to activate the relay.

P0888 concerns the relay output/sense circuit, where the TCM detects that the expected relay output is not present.

For example:

P0885: TCM cannot properly control the relay.

P0888: Relay output is not detected when it should be ON.

A P0885 fault can therefore potentially result in a P0888 condition.

P0885 vs. P0889

P0885 – TCM Power Relay Control Circuit/Open

There is an interruption in the relay control circuit.

P0889 – TCM Power Relay Sense Circuit Range/Performance

The relay sense signal or relay operation is outside the expected range or performance characteristics.

How to Diagnose P0885

The goal is to determine where the relay control circuit is interrupted.

1. Scan all control modules

Check:

• TCM

• ECM/PCM

• ABS module

• Body control module

• Other networked modules

Record all stored and pending codes.

2. Check related codes

Look for:

• TCM power codes

• Relay codes

• Low-voltage codes

• Communication codes

• CAN network codes

• Ignition power codes

3. Check freeze-frame data

Review:

• Battery voltage

• Engine RPM

• Vehicle speed

• Transmission temperature

• Ignition status

• TCM communication status

4. Identify the relay control circuit

Use the vehicle-specific wiring diagram to identify:

• Relay coil terminals

• Power supply

• Ground

• Control wire

• TCM control terminal

The circuit configuration differs between vehicles.

5. Check the relay

Test the relay according to manufacturer specifications.

Check:

• Coil resistance

• Relay activation

• Contact operation

• Correct relay type

If the relay coil is internally open, the relay must be replaced.

6. Check relay power

Verify that the relay receives the required supply voltage.

If power is missing, trace the circuit toward:

• Fuse

• Fuse box

• Ignition circuit

• Power distribution system

7. Check the relay control signal

Determine whether the TCM or another module is providing the required control signal.

If the control signal is missing, continue testing the wiring and module.

8. Inspect the relay socket

Look for:

• Loose terminals

• Corrosion

• Burn marks

• Damaged pins

• Poor terminal tension

9. Test wiring continuity

Check the control wire between the TCM and relay.

An open circuit may be caused by:

• Broken wire

• Disconnected connector

• Corroded terminal

• Damaged harness

10. Check for intermittent open circuits

A wire may be internally broken but still make contact under certain conditions.

Move the wiring harness carefully while monitoring the circuit.

11. Check TCM ground

Inspect and test the TCM ground circuit.

A poor ground can prevent proper relay control.

12. Check battery and charging voltage

Verify:

• Battery condition

• Battery terminals

• Charging voltage

• Main grounds

• Voltage stability

13. Inspect the wiring harness

Look for:

• Chafing

• Pinched wires

• Heat damage

• Broken conductors

• Corrosion

• Poor previous repairs

14. Check for water intrusion

Inspect:

• Fuse box

• Relay box

• TCM

• TCM connector

• Wiring harness

15. Perform a voltage-drop test

Check voltage drop across:

• Relay terminals

• Control wiring

• Power connections

• Ground connections

16. Evaluate the TCM

If the relay, wiring, connectors, power supply and grounds are all correct, the TCM may require further testing.

Why P0885 Can Be Misdiagnosed

P0885 can result in unnecessary TCM replacement if the technician does not trace the circuit properly.

For example:

Broken relay control wire → Relay cannot activate → TCM power unavailable → P0885

Replacing the TCM would not repair the broken wire.

Another example:

Corroded relay socket → Open control connection → Relay remains OFF → P0885

Again, the TCM may be perfectly functional.

The complete relay control circuit should therefore be tested before replacing the module.

P0885 After Battery Replacement

If P0885 appears after battery replacement, inspect:

• Battery terminals

• Main grounds

• Battery voltage

• TCM relay

• Fuse box

• Relay box

• TCM connectors

A disturbed or loose connection can cause an open circuit.

P0885 After Transmission Repair

If P0885 appears after transmission work, pay particular attention to:

• TCM connector

• Transmission harness

• Relay box

• Fuse box

• Ground connections

• Power connections

A wiring harness or connector may have been damaged or left disconnected during the repair.

P0885 After TCM Replacement

If P0885 appears after replacing the TCM, verify:

• Correct TCM

• Correct relay

• Correct relay control circuit

• Power supply

• Ground

• Wiring

• Connector installation

• Programming

• Vehicle configuration

A replacement TCM may require programming or configuration.

Can a Bad Relay Cause P0885?

Yes.

A failed relay coil can create an open circuit condition.

However, the relay should not automatically be blamed.

The technician should also check:

• Relay socket

• Relay power supply

• Control wiring

• Fuse

• TCM connector

• TCM ground

• TCM control output

Can P0885 Cause Transmission Problems?

Yes.

If the TCM power relay cannot be activated, the transmission control system may not receive the required electrical power.

Possible symptoms include:

• No gear selection

• Limp mode

• Harsh shifting

• Loss of reverse

• Loss of forward gears

• Transmission stuck in one gear

• Loss of drive

• TCM communication failure

Common Diagnostic Mistakes With P0885

Common mistakes include:

• Replacing the TCM immediately

• Replacing the transmission

• Replacing the relay without testing the circuit

• Ignoring the fuse

• Ignoring the relay socket

• Not checking relay power

• Not checking the relay control signal

• Failing to test wiring continuity

• Ignoring TCM grounds

• Ignoring battery voltage

• Not inspecting connectors

• Ignoring water intrusion

• Not checking related communication codes

What Is the Correct Repair for P0885?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Replacing a faulty TCM power relay

• Repairing a broken relay control wire

• Repairing an open circuit

• Reconnecting a loose connector

• Replacing damaged terminals

• Repairing the relay socket

• Replacing a damaged fuse or fuse terminal

• Repairing ignition power supply

• Cleaning corroded connectors

• Repairing TCM power connections

• Repairing TCM ground connections

• Repairing water intrusion

• Correcting battery or charging-system problems

• Replacing the TCM if confirmed faulty

• Programming or configuring the TCM where required

After completing the repair, clear the diagnostic codes and perform a complete transmission road test.

Final Thoughts on P0885

P0885 – Transmission Control Module (TCM) Power Relay Control Circuit/Open indicates that the TCM has detected an open or interrupted circuit in the electrical system used to control the TCM power relay.

The most important areas to inspect are the relay, relay socket, fuse, relay power supply, control wiring, connectors, TCM ground and TCM control circuit.

The key point is that P0885 does not automatically mean the TCM or transmission is defective. A broken wire, disconnected connector, corroded terminal or failed relay can prevent the power relay from activating.

A systematic electrical diagnosis should be performed before replacing the TCM or any internal transmission components.