P1870 - FAULT CODE - OBD2

POST UPDATED IN January, 2023

P1870 Code failures by brands

P1870 ACURA, BUICK, CADILLAC, CHEVROLET, GENERAL MOTORS, ISUZU: TRANSMISSION COMPONENT SLIPPING

Description of DTC code P1870

The Powertrain Control Module (PCM) monitors the rotational speeds of the input and output shaft to calculate different TCC (Torque Converter Clutch) engagement modulation strategies. They allow gear changes are smoother. However, it is necessary to state the TCC is designed to slip in certain amounts and conditions in most cases. This improves driving, as well as the lifetime of the different components.

On older GM vehicles, the P1870 OBDII fault code is set due to problems in the TCC solenoid many times. So, it causes the TCC hydraulic pressure to be lost. As a result, the slippage from the clutch is higher, which exceed the manufacturer’s limits. There are a lot of reasons for transmission slippage because of different designs, and they can be from any component.

When diagnostic code P1870 is set, it is because the PCM has found inconsistencies between the input and output shaft rotation speeds. While the transmission has been in top gear or when TCC or overdrive is activated.

Symptoms of fault code P1870

  • The Check Engine light turns on.
  • The transmission has different degrees of slippage.
  • Gear changes are harder than usual.

Causes of OBD2 P1870

The reasons why the DTC P1870 OBD2 DTC is stored are:

  • Transmission fluid may have contamination levels.
  • The valve body may have one or more bad valves.
  • Clutch packs may be damaged.
  • A pressure sensor may be in bad condition. This condition causes changes in the modulation time of the TCC.
  • The pressure pump may be defective.
  • If a trailer is used, the capacity of the trailer is greater than allowed.

Possible solutions of the DTC code P1870

The steps to solve the P1870 OBDII error code are the following:

  • Check if the manufacturer has provided Technical Service Bulletins (TSB) that match the year and model of your vehicle.
  • Scan your vehicle to check for other stored error codes. If these are related to transmission problems, diagnose those codes first.
  • Check the transmission fluid meets the requirements for good system performance. If the level or condition of the fluid is not suitable, make some repairs.
  • Consult the information manual for system specifications and diagnostic tests. Make fluid pressure tests, make adjustments if necessary.

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