P1864

Code

GMC P — Powertrain

Torque Converter Clutch Circuit

Brand: GMC

Type: P — Powertrain

Views: UK: 22 EN: 50 RU: 57

AI status

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Page language: EN

Causes

Open or shorted wiring in the TCC solenoid circuit
Corroded, loose, or damaged connector at the transmission or PCM/TCM
Failed TCC solenoid (stuck or electrically faulty)
Poor ground or low battery/charging system voltage
Blown fuse or faulty relay in transmission control power feed
Internal transmission valve body or hydraulic failure preventing TCC engagement

Symptoms

MIL (Check Engine) lamp illuminated
TCC not locking or converter slipping under load
Reduced fuel economy
Harsh or delayed shift feel
Transmission may enter limp mode or hold gears
Stored transmission fault codes and possible limp-home behavior

What to check

Read freeze frame and full code list with a capable scan tool; note any related transmission codes
Check battery state of charge and charging system voltage (stable ~12.6–14.4 V)
Visually inspect TCC solenoid connector and wiring for damage, corrosion, or pin push-out
Use scan tool to command TCC ON/OFF and watch live data (TCC requested vs TCC applied)
Measure voltage at the solenoid connector while commanding; check for PWM or switched 12V
Measure solenoid coil resistance at connector and compare to specification

Signal parameters

Nominal solenoid coil resistance: typically 10–50 ohms (spec varies by model) — check service spec
Supply voltage at solenoid when commanded ON: near battery voltage (~12 V) or PWM varying 0–12 V
Backfeed/idle voltage when OFF: near 0 V (or specified inactive level)
Command signal type: PWM duty cycle from PCM/TCM (frequency and duty vary by vehicle)
Expected current draw when energized: typically 0.3–3 A depending on solenoid design

Diagnostic algorithm

Verify: Retrieve P1864 and related codes; record freeze-frame and live data. Clear codes and attempt to re-create according to freeze-frame conditions.
Battery/Scan Tool: Confirm battery and charging system healthy. Use a scan tool to perform an active test on the TCC (command ON/OFF) while observing live parameters.
Visual Inspection: Inspect wiring harness from PCM/TCM to transmission, paying attention to chafing, pin corrosion, connector security, and water intrusion.
Voltage Test: With connector connected, backprobe the TCC solenoid harness. Command TCC ON and measure voltage at the solenoid power/command circuits. Compare to battery voltage and expected PWM.
Resistance Test: Isolate the solenoid connector and measure coil resistance with multimeter. Compare to service spec. An open or shorted coil indicates solenoid replacement.
Continuity/Short Test: Check continuity between the solenoid connector and PCM/TCM pins. Check for short to ground or battery on the control and power circuits.
Ground Check: Verify transmission case ground(s) and PCM/TCM ground(s) are clean and tight. Repair/clean as needed.
Functional Test: If wiring and PCM outputs are good but behavior persists, remove and bench-test or replace the TCC solenoid, or swap with a known-good solenoid if available.
Valve Body/Mechanical: If electrical components test good, inspect valve body and hydraulic circuits for stuck valves or internal leakage that prevent TCC engagement.
Finalize: After repair, clear codes, perform road test and monitor TCC operation with scan tool to confirm the fault does not return.
Safety note: Follow vehicle-specific procedures. Isolate battery when advised and avoid applying voltage to circuits unless using proper jigs and safety protections.

Likely causes

Damaged harness or pin corrosion at the transmission connector
TCC solenoid electrical failure (open or shorted coil)
Bad ground at transmission case or PCM/TCM connector
Intermittent connector contact (water intrusion / bent pins)
PCM/TCM output driver has failed (less common)

Fault status

⚠️ Status

Stored DTC P1864 — Torque Converter Clutch circuit fault detected. The PCM/TCM commanded the TCC but detected an open, short, incorrect voltage, or improper response from the TCC solenoid or circuitry. Inspect wiring, connectors, solenoid, grounds, and control module outputs.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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