P1871
Undefined Gear Ratio
P1871 is an OBD-II diagnostic trouble code meaning: Undefined Gear Ratio. Common causes: low transmission fluid level, friction disc wear. Estimated repair cost: $56–278.
Symptoms
- Erratic gear shifting
- Dips during acceleration
- Switching to emergency mode of automatic transmission operation
- Increased fuel consumption
- Check Engine Light Illuminates
Causes
- Low transmission fluid level
- Friction disc wear
- Malfunction of input/output shaft speed sensors
- Problems with the hydraulic block
- Transmission fluid contamination or degradation
How to Fix
- Check the level and condition of the transmission fluid
- Diagnose speed sensors and their circuits
- Check the hydraulic pressure in the system
- Perform computer diagnostics of automatic transmission
- If necessary, replace worn friction discs
Related codes
Error P1871 by Vehicle Brand
FAQ
What does the P1871 code mean?
P1871 is an OBD-II diagnostic trouble code that indicates: Undefined Gear Ratio
What causes a P1871 error code?
The most common causes of P1871 include: Low transmission fluid level; Friction disc wear; Malfunction of input/output shaft speed sensors; Problems with the hydraulic block.
How do I fix a P1871 diagnostic trouble code?
To fix P1871: Check the level and condition of the transmission fluid. Diagnose speed sensors and their circuits. Check the hydraulic pressure in the system. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P1871?
Do not drive — repair immediately
How much does it cost to fix P1871?
The estimated repair cost for P1871 is $56–278. Actual cost depends on your vehicle, location, and labor rates.
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