Faulty torque converter clutch solenoid or PWM solenoid, open or shorted internally; Damaged wiring or corroded connector between the transmission and the control module, including the internal harness on some models; Contaminated, degraded or incorrect transmission fluid affecting the solenoid and valve body; Faulty transmission control module driver circuit; Poor power or earth supply to the control module or solenoid, or low battery voltage; Worn valve body or internal hydraulic fault preventing correct TCC operation.

P1864

Torque Converter Clutch Circuit.

GM
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
8: AreaTransmission
64: FaultThe specific fault in that area

What it means

On GM vehicles P1864 means the transmission control module has found a fault in the torque converter clutch (TCC) circuit. It sets when the commanded state of the TCC solenoid or its driver does not match the electrical feedback, which points to an open circuit, short or failing component. The exact test and the circuit layout vary by model and transmission.

Symptoms

Malfunction indicator lamp on, sometimes with a transmission warning lamp
Torque converter clutch not locking up, so engine revs stay higher at cruising speed
Poorer fuel economy on steady motorway driving
Shudder or surging at light throttle if the clutch applies erratically
Transmission running hotter than normal
Possible stalling or a harsh feel when stopping if the clutch stays applied

Possible causes

Faulty torque converter clutch solenoid or PWM solenoid, open or shorted internallylikely
Damaged wiring or corroded connector between the transmission and the control module, including the internal harness on some modelslikely
Contaminated, degraded or incorrect transmission fluid affecting the solenoid and valve bodypossible
Faulty transmission control module driver circuitpossible
Poor power or earth supply to the control module or solenoid, or low battery voltagepossible
Worn valve body or internal hydraulic fault preventing correct TCC operationrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting speed, load and gear when the fault set, and check for related transmission or engine codes
Check the transmission fluid level, condition and smell, and compare against the manufacturer specification for your model
Inspect the wiring and the transmission connector for chafing, heat damage, water ingress, corrosion and bent or pushed-back pins
Check battery condition and charging voltage, plus power and earth supplies to the control module
Measure the TCC solenoid resistance at the transmission connector and compare it with the specification for that transmission
Test the solenoid circuit for continuity, short to earth and short to voltage between the connector and the control module
Use a scan tool with bidirectional control to command the TCC and watch the response and the slip speed
Check for applicable service bulletins and calibration updates for the vehicle and transmission

How to fix

Repair or replace damaged wiring, terminals or connectors found in the TCC circuit
Replace the TCC solenoid, or the solenoid assembly where it is not sold separately, if it is out of specification
Renew the transmission fluid and filter to the correct specification if it is contaminated or degraded
Repair power and earth supply faults and correct any battery or charging problem
Replace or repair the transmission control module only after the wiring and solenoid are proven good, and apply any manufacturer calibration update where it is a known cause

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but book it in soon. A TCC that stays unlocked or applies erratically can overheat the transmission fluid and worsen wear, so avoid heavy loads and long journeys.

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