P1870

Transmission Component Slipping

Car Fault Codes Chevrolet Transmission

Can you still drive? With care, short trips only

Who can fix it? Needs a specialist or dealer

Typical repair time 1 hour – 10 hours

Typical cost SAR 250 to 5,000

What it means

This is a Chevrolet (GM) manufacturer-specific code, and the same number can mean something different on other makes. The computer commanded torque converter clutch (TCC) lockup but saw a larger difference than allowed between engine speed and transmission input speed, meaning the lockup is slipping. On the 4L60-E and 4L65-E this is commonly linked to worn valve bores in the valve body, especially the TCC apply valve, or a worn clutch inside the torque converter.

Models covered: Chevrolet (GM) models with the 4L60-E/4L65-E automatic, mainly 1990s–2000s (e.g. Silverado, Tahoe).

Symptoms4

Engine rpm rising and falling at steady speed, as if slipping.
A light shudder at medium speeds.
Higher fuel consumption and hotter transmission fluid.
Check engine light on, and the computer may cancel lockup.

Possible causes5

Worn valve bores in the valve body, especially the TCC apply valve or TCC regulator valve bore.
A worn lockup clutch inside the torque converter.
Low or degraded transmission fluid.
A weak TCC PWM solenoid.
Low line pressure from pump wear or an internal leak (less common).

How to diagnose5

Check the transmission fluid level, condition and smell first.
Watch torque converter slip speed on a scan tool with lockup on, on a level road at steady speed.
Read other codes; P1860 points to the solenoid electrical circuit.
Have a transmission shop check line pressure and the valve body for bore wear.
If the valve body is good and slip continues, a worn converter clutch is likely.

How to fix5

Correct the fluid level and change fluid and filter if degraded.
Replace the TCC PWM solenoid if it is weak.
Repair the valve body with oversize valves and sleeves, or replace it.
Replace the torque converter if the lockup clutch is confirmed worn.
Clear the codes, drive on the highway and monitor slip to confirm 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.

A fluid service or solenoid is the low end, while valve body repair or a new torque converter requires transmission removal work and sits at the top of the range.

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

Will a fluid change fix P1870?

It helps if the fluid is low or degraded, but the common cause is mechanical wear in the valve body or converter, which fluid alone does not fix.

Why is the valve body mentioned so often with this code?

The TCC valve bores wear over time and leak pressure, so the lockup clutch does not hold well. Repairing these bores is a known fix on the 4L60-E.

Can I keep driving?

Short distances and gently, but slipping creates heat that damages the fluid and transmission. Avoid towing and heavy loads until it is repaired.

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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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