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P1870

Transmission Component Slipping.

  • Oldsmobile
  • 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 an Oldsmobile 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 points to a loss of clutch or band grip, or to a hydraulic pressure problem, rather than a simple sensor fault.

Symptoms

  • Engine revs rise during a gear change or under load without matching acceleration
  • Delayed, flared or soft shifts
  • Harsh or erratic engagement when selecting Drive or Reverse
  • Transmission warning light or check engine light on
  • Transmission stuck in one gear (limp mode) in some cases
  • Burnt smell from the transmission fluid

Possible causes

  • Low or degraded transmission fluid (wrong level, burnt or contaminated)likely
  • Worn clutch packs or bands inside the transmissionlikely
  • Low line pressure from a worn pump, blocked filter or internal fluid leakspossible
  • Faulty shift or pressure control solenoid, or a sticking valve bodypossible
  • Torque converter clutch slipping or failing to lock fullypossible
  • Faulty input or output speed sensor, or damaged wiring and connectors giving false slip readingspossible
  • Outdated transmission control module calibration (model and year dependent)rare

How to diagnose

  1. Read all stored codes and freeze frame data, noting road speed, gear commanded and engine load when the code set
  2. Check the transmission fluid level and condition, following the procedure for the specific model (some are checked hot, with the engine running)
  3. Inspect the wiring and connectors to the speed sensors and solenoids for damage, corrosion, chafing or fluid ingress
  4. Check for other related codes, such as speed sensor, solenoid or torque converter clutch faults, and deal with those first
  5. Watch live data for engine speed against input and output speed in each gear to find which gear or clutch is slipping
  6. Carry out a line pressure test using the manufacturer's specification for that transmission
  7. Check the transmission and engine mounts and the cooler lines for leaks or restrictions
  8. Check for any applicable calibration updates for the control module on that model and year

How to fix

  • Correct the fluid level and replace the fluid and filter if it is burnt or contaminated, then find and fix any leak
  • Replace faulty speed sensors or repair damaged wiring and connectors
  • Replace the faulty solenoid or overhaul the valve body if it is sticking or worn
  • Rebuild or replace the transmission if the clutches, bands or pump are worn
  • Repair or replace the torque converter if it is slipping or failing to lock
  • Apply a calibration update to the control module if it is a known fix for the specific model

Can I keep driving?

High severity

Limit driving and avoid heavy loads or towing, as continued slipping can quickly burn out the clutches and cause expensive damage. Have it checked as soon as possible, and stop driving if the slipping gets worse or the transmission overheats.

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

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