Faulty TCC solenoid or TCC pulse width modulation solenoid inside the transmission; Damaged, chafed or corroded wiring between the transmission and the control module, or an internal transmission harness fault; Poor connection at the transmission connector or control module connector, with corrosion, bent pins or water ingress; Contaminated, degraded or incorrect level of transmission fluid affecting solenoid operation; Fault in the transmission control module or its driver circuit; Mechanical fault in the torque converter or valve body causing a related performance fault.

P1864

Torque Converter Clutch Circuit.

GMC
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

P1864 on a GMC means the transmission control module has detected a fault in the torque converter clutch (TCC) circuit. The TCC solenoid or its control circuit is not behaving as commanded, for example through an open circuit, a short, or an electrical reading outside the expected range. The exact test the module runs and the way the fault is detected vary by model, engine and transmission.

Symptoms

Malfunction indicator lamp or transmission warning lamp on
Torque converter clutch not locking up, with higher engine revs at cruising speed
Worse fuel economy on steady motorway driving
Shudder or surging at light throttle and steady speed
Transmission running hotter than normal
Transmission may be held in a default mode or shift quality may change

Possible causes

Faulty TCC solenoid or TCC pulse width modulation solenoid inside the transmissionlikely
Damaged, chafed or corroded wiring between the transmission and the control module, or an internal transmission harness faultlikely
Poor connection at the transmission connector or control module connector, with corrosion, bent pins or water ingresslikely
Contaminated, degraded or incorrect level of transmission fluid affecting solenoid operationpossible
Fault in the transmission control module or its driver circuitrare
Mechanical fault in the torque converter or valve body causing a related performance faultrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting the speed, load and temperature when the fault set, and check for any related codes
Check transmission fluid level, condition and smell against the manufacturer's procedure, looking for burnt fluid or debris
Inspect the wiring and connectors from the transmission to the control module for chafing, heat damage, corrosion, moisture and pin tension
Check the supply and ground to the TCC solenoid circuit with a multimeter, following the wiring diagram for the specific model and transmission
Measure the TCC solenoid resistance at the transmission connector and compare it with the specification for that transmission
Use a scan tool to command the TCC and watch the commanded duty cycle against the actual response and the slip speed
Check for any technical service bulletins or calibration updates relevant to the vehicle
If the circuit and solenoid test correctly, investigate the valve body and torque converter as the procedure for that transmission directs

How to fix

Repair or replace damaged wiring and fix any short or open circuit found
Clean or replace corroded or damaged connectors and terminals
Replace the TCC solenoid, or the solenoid assembly, if its resistance or operation is out of specification
Correct the fluid level, or change the fluid and filter if it is contaminated, using the specified fluid
Update or replace the control module only if testing proves it faulty or an outdated calibration is a known cause for that model
Repair or replace the valve body or torque converter if mechanical faults are confirmed

Can I keep driving?

Medium severity

The vehicle can usually be driven for a short time, but the book-in should be soon. Running without converter lock-up can overheat the fluid and cause extra transmission wear, so avoid towing and long, high-speed journeys until it is repaired.

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