Dirty or carbon-fouled throttle body causing the plate to stick or move sluggishly; Faulty throttle body or internal throttle motor or position sensors; Damaged wiring, corroded terminals or loose connector at the throttle body or accelerator pedal sensor; Faulty accelerator pedal position sensor giving implausible readings; Low or unstable supply voltage or poor earth, from a weak battery or charging fault; Fault within the powertrain control module or its throttle driver circuit.

P1589

Throttle Control Unit Unable To Control Desired Throttle Angle.

Mercury
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
5: AreaVehicle speed, idle control and auxiliary inputs
89: FaultThe specific fault in that area

What it means

P1589 on a Mercury means the throttle control unit could not make the throttle plate reach the angle the powertrain control module asked for. The electronic throttle system compared the requested angle with the position fed back by the throttle position sensors and found a mismatch it could not correct. The car will usually drop into a reduced-power fail-safe mode.

Symptoms

Engine warning light on, often with a throttle or power reduced warning
Limited engine power or the car stuck in a restricted 'limp' mode
Poor or delayed throttle response
Unstable, high or low idle, or stalling
Hesitation or surging when pulling away

Possible causes

Dirty or carbon-fouled throttle body causing the plate to stick or move sluggishlylikely
Faulty throttle body or internal throttle motor or position sensorslikely
Damaged wiring, corroded terminals or loose connector at the throttle body or accelerator pedal sensorpossible
Faulty accelerator pedal position sensor giving implausible readingspossible
Low or unstable supply voltage or poor earth, from a weak battery or charging faultpossible
Fault within the powertrain control module or its throttle driver circuitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note any related throttle, pedal or voltage codes
Check battery condition and charging voltage, and inspect the main earths and power feeds
Inspect the throttle body wiring and connector, and the pedal sensor connector, for damage, corrosion, water ingress or poor pin tension
Look at the throttle plate and bore for heavy carbon build-up or sticking, following the model-specific procedure for the throttle body
With a scan tool, compare requested and actual throttle angle and the pedal and throttle sensor readings through the full range of travel, looking for jumps or dropouts
Wiggle-test the harness with live data showing, to find intermittent faults
Check the throttle motor drive circuit and sensor reference and signal circuits for resistance, shorts and voltage against the wiring diagram for your model and engine
Where the throttle body is replaced or cleaned, carry out the throttle relearn or adaptation that the model requires

How to fix

Clean the throttle body carefully using a method suited to electronic throttles, then perform the relearn procedure
Repair or replace damaged wiring, terminals or connectors found in the throttle or pedal circuits
Replace the throttle body if the motor or sensors are faulty or the plate sticks, then complete the relearn
Replace the accelerator pedal assembly if its sensor readings are implausible
Restore proper battery, charging and earth condition if voltage is the cause
Repair or replace the powertrain control module only after all other causes are ruled out, with any needed calibration update

Can I keep driving?

Medium severity

The car may be limited in power and can respond unpredictably, so avoid driving it except to reach a workshop. Stop driving if the throttle sticks, the idle is erratic or the engine stalls, as this is a safety risk in traffic.

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