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P1870

Transmission Component Slipping.

  • Buick
  • Powertrain
  • Manufacturer code
  • High severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
8
AreaTransmission
70
FaultThe specific fault in that area

What it means

P1870 on a Buick means the transmission control module has detected that a component inside the automatic transmission is slipping. It sets when the measured relationship between engine speed and transmission input or output speed does not match the gear or clutch the module has commanded. This usually points to a clutch, band, torque converter clutch or hydraulic pressure problem, though the exact cause depends on the model and transmission fitted.

Symptoms

  • Engine revs rise without matching acceleration, especially during gear changes
  • Delayed, flared or soft shifts between gears
  • Transmission warning or check engine light on
  • Harsh shifting or the car dropping into limp mode
  • Burning smell or discoloured transmission fluid
  • Poor acceleration or loss of power when pulling away or under load

Possible causes

  • Low or degraded transmission fluid, or the wrong fluid typelikely
  • Worn clutch packs or bands inside the transmissionlikely
  • Low line pressure from a worn pump, blocked filter or internal leakspossible
  • Faulty shift solenoid or pressure control solenoidpossible
  • Torque converter clutch slipping or failingpossible
  • Faulty input or output speed sensor giving inaccurate readings, or damaged wiring or connectorspossible
  • Valve body wear or sticking valvesrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting speed, gear, load and temperature when the code set, and check for other transmission or engine codes
  2. Check the transmission fluid level, condition and smell using the correct procedure for the model, and look for leaks
  3. Inspect wiring and connectors to the transmission, speed sensors and solenoids for damage, corrosion or fluid contamination
  4. Check for other faults that could cause slip-like symptoms, such as misfires or engine torque problems
  5. Using live data, compare engine speed, input speed and output speed in each gear and note when slip appears
  6. Check commanded against actual line pressure and the torque converter clutch slip figures where the model supports it
  7. Test solenoid and speed sensor resistance and operation against the manufacturer's specification for that transmission
  8. Road test and note which gear or shift is affected to narrow down the clutch or band involved

How to fix

  • Correct the fluid level and replace degraded fluid and filter with the specified type
  • Replace faulty speed sensors, solenoids or damaged wiring and connectors
  • Repair or replace the valve body or pump if pressure is low
  • Replace or repair the torque converter if the clutch is slipping
  • Overhaul or replace the transmission if clutches or bands are worn
  • Apply any manufacturer software update for the transmission control module only if one is known to address the fault

Can I keep driving?

High severity

Limit driving and avoid heavy loads or towing, as continued slipping can quickly burn clutches and cause expensive damage. Have it inspected as soon as possible, and stop driving if slip is severe or the car loses drive.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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