Code Definition

P1870 — Automatic transmission slipping

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Honda

About P1870

P1870 is a manufacturer-specific powertrain diagnostic trouble code recorded for Honda vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1870 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This DTC is set when the Powertrain Control Module (PCM) or Transmission Control Module (TCM) detects excessive slip inside the transmission during gear or torque converter clutch engagement. The module compares input shaft or engine speed against output shaft or transmission speed, and a clutch or converter that is holding correctly should keep that speed difference within a tight calibrated window. P1870 sets when the measured slip exceeds the calibrated threshold under steady state driving, which indicates degraded hydraulic pressure or worn mechanical friction elements. The driver typicall...

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