P1860: TCC PWM Solenoid Circuit Electrical (GM)
Severity: medium
What it means: On many GM vehicles, the computer sees an electrical fault in the torque converter clutch (TCC) solenoid circuit. That solenoid controls the clutch that locks the torque converter at cruising speed for better mileage.
Safe to drive? Usually drivable for short trips, but the computer may stop locking the converter, which can raise transmission temperature and lower mileage. Get it checked soon.
Common symptoms
- Check-engine light
- Converter never locks up (higher rpm at cruise)
- Worse fuel economy
- Other transmission codes may be stored too
Likely causes, ranked
- Open or shorted wiring, or a poor connectorShop
- Blown ignition fuse feeding the solenoidDIY
- Faulty TCC PWM solenoidShop
- Computer (PCM) driver fault (rare)Shop
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Vehicle-specific notes
- 1995–1999 Buick Riviera: A 1997 Riviera 3.8 supercharged owner had P0753, P0758 and P1860 together; new shift solenoids and fluid didn't help and the shop said the transmission needed replacing. Read the full answer · Source
DIY or shop?
Checking the fuse and fluid is DIY. The solenoid sits on the valve body inside the transmission, so testing and replacement are usually shop work.
Before you replace parts
- Check transmission fluid level and condition first.
- Read all stored codes. Several solenoid codes at once can point to shared wiring, a fuse or the connector rather than every solenoid.
- Have the solenoid circuit and resistance tested before replacing parts.
- Check your VIN for recalls and service bulletins.
Safety / mechanic note
Verify with a mechanic. An overheating transmission can fail. Watch for slipping or a burnt smell. A code points to a circuit or system, not always a specific part.
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