Faulty TCM power relay (contacts stuck or internal fault); Wiring fault in the relay control circuit, such as a short to voltage or damaged insulation; Corroded, loose or damaged connectors at the relay, fuse box or TCM; Low or unstable battery or charging system voltage affecting the circuit readings; Faulty TCM (internal driver circuit failure); Water ingress into the TCM, relay box or wiring connector; Outdated TCM software where a known fault with relay monitoring has been documented by the manufacturer.

P0887

TCM Power Relay Control Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0887 is a generic powertrain code meaning the transmission control module (TCM) has detected a high voltage state on the control circuit for its power relay. The TCM commands the relay on or off and monitors the circuit, and it set the code when the circuit voltage did not match the commanded state, for example staying high when it should have been pulled low. Exact relay layout and how the circuit is monitored vary by model and transmission.

Symptoms

Transmission warning light or malfunction indicator lamp on
Transmission stuck in one gear (limp mode)
Harsh, delayed or erratic gear changes
No gear changes or no drive in some cases
Gearbox failing to select ranges or engage after restart
Reduced performance or poor fuel economy

Possible causes

Faulty TCM power relay (contacts stuck or internal fault)likely
Wiring fault in the relay control circuit, such as a short to voltage or damaged insulationlikely
Corroded, loose or damaged connectors at the relay, fuse box or TCMpossible
Low or unstable battery or charging system voltage affecting the circuit readingspossible
Faulty TCM (internal driver circuit failure)possible
Water ingress into the TCM, relay box or wiring connectorrare
Outdated TCM software where a known fault with relay monitoring has been documented by the manufacturerrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including battery voltage and when the fault occurred
Check battery condition and charging voltage, as low or unstable voltage can cause false circuit faults
Inspect the relevant fuses and the TCM power relay for damage, heat marks or corrosion
Visually inspect the wiring and connectors between the relay, fuse box and TCM for chafing, water ingress, green corrosion or pushed-back pins
Swap in a known good relay of the same type, if the manufacturer's wiring diagram confirms it is interchangeable, and retest
With the relay removed or the harness disconnected, test the control circuit for short to voltage, short to earth and continuity against the wiring diagram
Check the relay supply and earth feeds under load using a voltage drop test
Check for manufacturer service bulletins or software updates relating to the TCM and relay, then clear the code and road test to see if it returns

How to fix

Replace the faulty TCM power relay
Repair or replace damaged wiring in the relay control circuit
Clean or replace corroded or damaged connectors and terminals
Repair the battery or charging system fault
Replace or repair the TCM if it is confirmed faulty, and have it coded or programmed as required for the vehicle
Update the TCM software only if the manufacturer lists it as a fix for this fault

Can I keep driving?

Medium severity

The car may be driveable in limp mode, but gearbox behaviour can be unpredictable, so have it checked soon. If it will not select gears or loses drive, stop driving and arrange recovery.

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