P1860

TCC PWM Solenoid Circuit Electrical

Car Fault Codes GMC Transmission

Can you still drive? With care, short trips only

Who can fix it? Needs a workshop

Typical repair time 1 hour – 4 hours

Typical cost SAR 100 to 1,500

What it means

This is a GMC manufacturer-specific code, and the same number can mean something different on other makes. The computer controls torque converter clutch (TCC) lockup with a pulsed signal to a solenoid inside the transmission, and this code means it found an electrical fault in that circuit. Lockup is usually cancelled, so the transmission no longer gives a direct engine-to-wheel link at higher speeds.

Models covered: GMC models with the 4L60-E/4L80-E automatic, mainly 1990s–2000s (e.g. Sierra, Yukon).

Symptoms4

Engine rpm slightly higher than usual on the highway.
Hotter transmission fluid, especially when towing or in summer.
Higher fuel use on long trips.
Check engine light on.

Possible causes5

Fluid inside the transmission case connector or corroded terminals.
Heat damage to the internal transmission harness.
A burned-out TCC PWM solenoid coil.
Damaged external wiring near the exhaust or frame.
An engine or transmission computer fault (rare).

How to diagnose5

Unplug the transmission connector and inspect it for fluid or corrosion.
Measure the solenoid circuit resistance from the transmission side and from the computer side and compare with specification.
Inspect the external wiring along its route for chafing or burns.
Command the solenoid with a scan tool and watch the circuit status.
If readings from the transmission side are wrong, inspect the internal harness and solenoid after removing the pan.

How to fix5

Clean the connector and replace its seal.
Repair the external wiring and route it away from heat.
Replace the internal harness if damaged.
Replace the TCC PWM solenoid with a fluid and filter change.
Clear the codes, drive on the highway and confirm lockup and that the code does not return.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for cleaning the connector or fixing a wire, and higher when the pan must come off to replace the solenoid or harness.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Can I tow with this code?

Better not. Without converter lockup, transmission fluid heats up quickly when towing or hauling, which shortens transmission life.

Does this code mean the torque converter is bad?

No. This is an electrical code for the solenoid circuit. If lockup works but slips, that is a different code, P1870.

Why change the fluid along with the solenoid?

The pan is off anyway, and heat-degraded fluid affects valve operation, so fresh fluid protects the repair.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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