What does it mean?
P1870 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Transmission Component Slipping Malfunction .
Symptoms
- Engine rpm flares between shifts while road speed barely changes
- Vehicle accelerates poorly for the engine speed, especially uphill or loaded
- Slipping felt most under acceleration or when the fluid is hot
- Burnt smell from the transmission fluid and a hot-running transmission
- Malfunction indicator lamp on, often with additional ratio or gear codes
- Delayed engagement when selecting Drive or Reverse
Likely causes
- Low transmission fluid level or burnt, oxidised fluid that can no longer hold pressure
- Worn clutch packs or bands that no longer hold torque
- Worn torque converter clutch lining allowing constant slip
- Low line pressure from a weak pump, worn pressure control solenoid or leaking sealing rings
- Clogged filter starving the pump and dropping pressure under load
- Worn valve body bores letting apply pressure bleed off
- Speed sensor or reluctor problems giving the module a false slip calculation
How to fix it
- Check fluid level with the transmission at operating temperature; note colour and smell
- Read all codes and freeze frame data to see the load and speed when slip was detected
- Log engine rpm, input speed, output speed and gear ratio during a road test to identify which element slips
- Perform a line pressure test where a pressure tap is available and compare with specification
- Drop the pan and inspect the filter and magnet for friction material or metal
- If only the fluid is degraded, service the fluid and filter, reset adaptives and retest
- If slip is confirmed mechanically, plan internal repair of the affected clutch or the converter