Faulty or failing TCM power relay (worn contacts or coil); Corroded, loose or damaged connectors and terminals at the relay, fuse box or TCM; Wiring fault in the relay control circuit, such as a short to earth or high resistance; Low battery voltage or poor charging system performance; Blown or poor-contact fuse in the relay supply or output; Internal fault in the TCM relay driver; Water ingress into the transmission connector or harness.

P0886

TCM Power Relay Control Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
86: FaultThe specific fault in that area

What it means

P0886 means the transmission control module (TCM) has detected a low voltage signal in the control circuit for its power relay, which is the relay that supplies switched power to the TCM or transmission solenoids. The TCM compared the commanded state of the relay circuit with the voltage it actually saw and found it lower than expected. The exact circuit layout, and whether the relay is separate or built into another module, depends on the vehicle.

Symptoms

Gearbox warning light or malfunction indicator lamp on
Transmission stuck in one gear (limp mode)
Harsh, delayed or flared gear changes
No shifting or loss of drive in severe cases
Gear selector position not shown correctly or erratic on the display
Intermittent fault that comes and goes with vibration or temperature

Possible causes

Faulty or failing TCM power relay (worn contacts or coil)likely
Corroded, loose or damaged connectors and terminals at the relay, fuse box or TCMlikely
Wiring fault in the relay control circuit, such as a short to earth or high resistancelikely
Low battery voltage or poor charging system performancepossible
Blown or poor-contact fuse in the relay supply or outputpossible
Internal fault in the TCM relay driverrare
Water ingress into the transmission connector or harnessrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including battery voltage, to see when the fault set
Check battery condition and charging voltage, as low system voltage can set or mimic this fault
Visually inspect the relevant fuses, relay and fuse box for heat damage, corrosion or water ingress
Inspect the TCM, relay and transmission connectors for bent, pushed-out or corroded terminals
Check the relay itself using the manufacturer's procedure, including coil resistance and contact operation, or swap with a known good identical relay if the layout allows
Using the wiring diagram for the model, test the relay control circuit for short to earth, open circuit and voltage drop
Check the relay supply and earth feeds to the TCM under load
Clear the code and road test, monitoring live data to see if the fault returns

How to fix

Replace the faulty TCM power relay with a correct specification part
Clean or repair corroded terminals and connectors, and secure any loose pins
Repair or replace damaged wiring in the relay control circuit
Replace blown fuses only after finding and fixing the cause of the overload
Recharge or replace a weak battery and repair any charging system fault
Repair or replace the TCM if testing proves the relay driver is faulty, followed by any programming the manufacturer requires

Can I keep driving?

Medium severity

The car may enter limp mode or lose drive without warning, so avoid long journeys and book a diagnosis soon. Stop driving if the gearbox will not select gears or shifts become harsh or unsafe.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.