Transmission Component Slipping
2002-2009 GMC Envoy 4.2L I6 🇩🇪
Description
The TCM detected transmission slipping during cruise conditions. Once the vehicle reaches cruise state, the TCM monitors the transmission ratio. If slipping is detected, P1870 sets and line pressure is elevated to stop further slippage. This code is extremely common on GM vehicles with the 4L60E transmission.
Symptoms
- Check Engine Light
- Harsh 1-2 shift
- Transmission slipping
- Fourth gear may become unavailable
- Higher RPMs than normal
- Poor fuel economy
- General poor transmission performance
Common Causes
- Worn or failed TCC (Torque Converter Clutch) solenoid valve causing pressure loss (most common on 4L60E)
- Dirty, degraded, or contaminated transmission fluid
- Defective or sticking valve body shuttles
- Excessive wear in TCC isolator/regulator valve bore
- Worn transmission clutch packs
- Low transmission fluid level
- Internal transmission seal leaks
Diagnostic Steps
- Check transmission fluid level and condition
- Monitor transmission slip rate with scan tool
- Test TCC solenoid valve
- Inspect valve body for worn bores
- Test line pressure at all gear ranges
- Check for TCC apply and release
Repair Notes
On 4L60E transmissions, the TCC solenoid is almost always the root cause. Change fluid and filter, then replace TCC solenoid. If code returns, valve body bore wear may require a remanufactured valve body or transmission rebuild.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
P1870 on Other Vehicles
Common Questions
What does code P1870 mean on a 2002-2009 GMC Envoy?
P1870 stands for "Transmission Component Slipping". The TCM detected transmission slipping during cruise conditions. Once the vehicle reaches cruise state, the TCM monitors the transmission ratio. If slipping is detected, P1870 sets and line pressure is elevated to stop further slippage. This code is extremely common on GM vehicles with the 4L60E transmission.
What are the symptoms of P1870 on a GMC Envoy?
Common symptoms of P1870 include: Check Engine Light, Harsh 1-2 shift, Transmission slipping, Fourth gear may become unavailable, Higher RPMs than normal, Poor fuel economy, General poor transmission performance.
What causes P1870 on a 2002-2009 GMC Envoy?
Common causes of P1870 include: Worn or failed TCC (Torque Converter Clutch) solenoid valve causing pressure loss (most common on 4L60E), Dirty, degraded, or contaminated transmission fluid, Defective or sticking valve body shuttles, Excessive wear in TCC isolator/regulator valve bore, Worn transmission clutch packs, Low transmission fluid level, Internal transmission seal leaks.