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GTECH Calibration
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P1864

Torque Converter Clutch Circuit.

  • Buick
  • 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 Buick means the transmission control unit has detected a fault in the torque converter clutch (TCC) circuit. The control unit commands the clutch solenoid or its control circuit and compares the electrical response or the resulting converter behaviour with what it expects. If the circuit reads open, shorted or out of range, the code is set. Exact test conditions and circuit layout vary by model, engine and transmission, so check the manufacturer data for the vehicle.

Symptoms

  • Malfunction indicator lamp or transmission warning lamp on
  • Torque converter clutch not locking up, or locking intermittently
  • Higher engine revs at cruising speed and worse fuel economy
  • Shudder or judder at steady speeds
  • Transmission running hotter than normal
  • Transmission held in a limited operating mode on some models

Possible causes

  • Faulty torque converter clutch solenoid or PWM solenoidlikely
  • Damaged wiring, chafed loom or corroded connector between the control unit and the solenoidlikely
  • Internal transmission wiring harness or connector faultpossible
  • Low, degraded or contaminated transmission fluid affecting the solenoid and clutch operationpossible
  • Worn torque converter clutch or internal converter faultpossible
  • Faulty transmission or powertrain control module, or a driver circuit fault within itrare

How to diagnose

  1. Read all stored and pending codes and the freeze frame data, noting speed, load and fluid temperature when the fault set
  2. Check the transmission fluid level, condition and smell, following the procedure for the specific transmission
  3. Inspect the wiring and connectors to the transmission and the control unit for chafing, heat damage, corrosion and water ingress
  4. Check battery condition and charging voltage, as low or unstable voltage can upset solenoid circuits
  5. Use a scan tool to command the torque converter clutch and watch the commanded against actual slip speed
  6. Measure the solenoid resistance and compare it with the manufacturer specification for that transmission
  7. Check the solenoid circuit for open circuit, short to earth and short to voltage with the connectors disconnected
  8. Look for any technical service bulletins or calibration updates relevant to the vehicle and code

How to fix

  • Replace the torque converter clutch solenoid if its resistance or operation is out of specification
  • Repair or replace damaged wiring, terminals or connectors in the solenoid circuit
  • Replace the internal transmission harness or connector if it is found faulty
  • Correct the fluid level or replace degraded fluid and filter as the manufacturer specifies
  • Repair or replace the torque converter if the clutch is worn or slipping mechanically
  • Repair or replace the control unit, or apply an updated calibration, only when testing confirms it is the cause

Can I keep driving?

Medium severity

The car can usually be driven a short distance to get it checked, but avoid heavy loads and long journeys. A converter clutch that slips or shudders can overheat the transmission fluid and cause further wear, so get it diagnosed soon.

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

This code for other makes

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