Faulty or sticking TCM power relay (or the relay contacts burnt or worn); Corroded, loose or damaged connectors and terminals in the relay or TCM supply circuit; Open circuit, high resistance or short in the relay sense or power supply wiring; Blown or poorly seated fuse feeding the TCM or relay; Weak battery, poor earth connections or charging system fault causing low or unstable voltage; Internal fault in the TCM or integrated mechatronic unit; Outdated TCM software where the manufacturer has issued a fix for the relay monitoring.

P0889

TCM Power Relay Sense Circuit Range/Performance.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0889 is the generic code for a range or performance fault in the transmission control module (TCM) power relay sense circuit. The TCM monitors the voltage at the relay output and compares it with what it expects from the relay command and system voltage. If the sensed voltage does not match the commanded relay state, or is out of the expected range, the code is set.

Symptoms

Gearbox warning light or malfunction indicator lamp on
Transmission stuck in one gear (limp mode)
Harsh, delayed or erratic gear changes
No shift or no drive engagement
Intermittent loss of gearbox function, especially over bumps or when wet
Reduced performance or poor fuel economy

Possible causes

Faulty or sticking TCM power relay (or the relay contacts burnt or worn)likely
Corroded, loose or damaged connectors and terminals in the relay or TCM supply circuitlikely
Open circuit, high resistance or short in the relay sense or power supply wiringlikely
Blown or poorly seated fuse feeding the TCM or relaypossible
Weak battery, poor earth connections or charging system fault causing low or unstable voltagepossible
Internal fault in the TCM or integrated mechatronic unitrare
Outdated TCM software where the manufacturer has issued a fix for the relay monitoringrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting battery voltage and conditions when the fault set, and check for other power supply or communication codes.
Test the battery and charging voltage, and check the battery terminals and main earths for tightness and corrosion.
Inspect the fuses and relay for the TCM supply (locations depend on model) and check for heat damage or poor contact.
Visually inspect the TCM, gearbox connector and relay wiring for chafing, water ingress, corrosion and pushed-out pins.
With the relevant wiring diagram, check the supply, earth and sense circuit for voltage drop, continuity and shorts while wiggling the harness.
Swap in a known good relay of the same specification, if it is a removable type, or test the relay coil and contacts on the bench.
Use a scan tool's live data to watch the commanded relay state against the sensed voltage while operating the ignition.
Check for any manufacturer software updates or technical bulletins for the model and gearbox before condemning the TCM.

How to fix

Replace the faulty TCM power relay with one of the correct specification.
Clean or repair corroded or damaged connectors and terminals, and secure any loose pins.
Repair or replace damaged wiring in the relay supply, earth or sense circuit.
Replace blown fuses only after finding and fixing the cause of the overload.
Restore proper system voltage by repairing the battery, earths or charging system.
Repair, replace or reprogram the TCM or mechatronic unit only once the wiring and relay are proven good, following the manufacturer's procedure.

Can I keep driving?

Medium severity

The car may be driveable in limp mode, but gearbox behaviour can be unpredictable or it may lose drive altogether. Get it checked soon and avoid long journeys or heavy loads until it is fixed.

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