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P1860

TCC PWM Solenoid Circuit Electrical.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
8
AreaTransmission
60
FaultThe specific fault in that area

What it means

On a Buick, P1860 means the transmission control module has detected an electrical fault in the torque converter clutch (TCC) pulse width modulated solenoid circuit. The module drives the solenoid with a PWM signal to lock and unlock the converter clutch smoothly, and it saw a voltage or current that did not match what it commanded, such as an open circuit, a short to ground or a short to voltage.

Symptoms

  • Malfunction indicator lamp or transmission warning lamp on
  • Torque converter clutch not locking up, or locking harshly
  • Higher engine revs at steady cruising speed
  • Poorer fuel economy
  • Shudder or surge at light throttle at motorway speeds
  • Transmission running hotter than normal

Possible causes

  • Damaged wiring or chafed loom to the TCC PWM solenoid (open circuit, short to ground or short to voltage)likely
  • Corroded, loose or contaminated connector at the transmission or at the control modulelikely
  • Faulty TCC PWM solenoid with an internal open or short, or out-of-range resistancelikely
  • Contaminated or degraded transmission fluid, or debris affecting the solenoidpossible
  • Internal transmission harness fault or damaged pass-through connectorpossible
  • Faulty transmission control module or driver circuitrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting speed, load and temperature when the code set, then check for related transmission or battery voltage codes
  2. Check battery condition and charging voltage, as low or unstable voltage can upset solenoid circuit monitoring
  3. Visually inspect the wiring and connectors between the transmission and the control module for chafing, heat damage, corrosion and water ingress
  4. Check transmission fluid level and condition, looking for a burnt smell, dark colour or debris
  5. Measure the TCC PWM solenoid resistance at the transmission connector and compare it with the specification for that model and transmission
  6. Check the solenoid feed and control circuits for continuity, short to ground and short to voltage, following the wiring diagram for the vehicle
  7. Use a scan tool to command the TCC solenoid and watch the response, or monitor the signal with a scope if available
  8. Check for any technical service information or software updates relevant to the model before condemning the control module

How to fix

  • Repair or replace damaged wiring and terminals in the TCC solenoid circuit
  • Clean, secure or replace corroded or loose connectors
  • Replace the TCC PWM solenoid if its resistance or operation is out of specification
  • Replace the internal harness or pass-through connector if tested faulty (access depends on the transmission fitted)
  • Service the transmission with the correct fluid and filter if the fluid is contaminated
  • Replace or repair the transmission control module only after wiring and solenoid faults are ruled out, with any required programming

Can I keep driving?

Medium severity

The car can usually be driven short distances, but without converter lock-up the transmission may run hotter and use more fuel. Book it in soon and avoid heavy loads or towing until it is repaired.

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

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