What does P1871 mean on a Chevy?

P1871. Undefined gear ratio. Measured gear ratio matches no known gear. Applies to Silverado, Sierra, Tahoe, Suburban with 4L60E 1996 to 2006. S10, Blazer with 4L60E..

What causes P1871 on a Chevy?

Slipping clutches or band Faulty input speed sensor Faulty output speed sensor Low fluid pressure Worn valve body bores

How do I fix P1871 on a Chevy?

Check fluid level and condition Compare input and output speed data Test line pressure Inspect for other slip codes Rebuild as tests indicate

Code

P1871

Undefined gear ratio

Category: Powertrain - Transmission
Severity: Check Engine Light
Applies to: Silverado, Sierra, Tahoe, Suburban with 4L60E 1996 to 2006. S10, Blazer with 4L60E.
Related: No single generic twin. See OBD Codes List

What it means

P1871. Undefined gear ratio. Measured gear ratio matches no known gear. This Chevy-enhanced code applies to Silverado, Sierra, Tahoe, Suburban with 4L60E 1996 to 2006. S10, Blazer with 4L60E..

Findings, check these first

Slipping clutches or band
Faulty input speed sensor
Faulty output speed sensor
Low fluid pressure
Worn valve body bores

Standard procedure

Check fluid level and condition
Compare input and output speed data
Test line pressure
Inspect for other slip codes
Rebuild as tests indicate

Look up another code

Press / to jump to the box. Chevy-enhanced powertrain, body, chassis and network codes.

Sources and review

Review: checked against the recorded source material.

P1871 Undefined Gear Ratio
archived reference page (autocodes.com via Wayback Machine)
Supports: code identity and GM application (page lists P1871 BUICK and P1871 CADILLAC variants)
Fetched generic page lists Buick and Cadillac GM variants, both undefined gear ratio, matching the catalog. No Chevrolet-specific page is archived. Model and year fitment remain curator claims.

Last updated 2026-09-25.

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