P1870 on Buick
Transmission Component Slipping
P1870 on Buick vehicles indicates transmission component slipping. Au7o has documented this code across 1 Buick model — most commonly on Roadmaster. This manufacturer-specific code (common on GM and Ford automatics, e.g. 4L60E) means the computer detected slippage between transmission components, most often at the torque converter clutch, where commanded engagement does not match actual behavior. When it sets, the PCM typically raises line pressure to protect the transmission and may lock out the converter clutch. Symptoms include harsh or delayed shifts, RPM flare/slipping, and reduced fuel economy. It often points to a worn valve body bore or TCC components and should be addressed before further internal damage occurs. Typical repair costs on Buick range from $1,500 to $3,000, depending on the specific model and root cause.
Common Causes of P1870
- •Worn torque converter clutch (TCC) regulator valve bore in the valve body
- •Faulty TCC solenoid or PWM solenoid
- •Worn or failing torque converter clutch
- •Low or degraded transmission fluid
- •Worn internal clutches or seals (e.g., input shaft O-ring)
- •Worn valve body / internal hydraulic leak
P1870 on Buick by Model
Buick Roadmaster(1 issue)
- 4L60E automatic transmission wear (valve body, sprag, harsh shift/no downshift)1994-1996
The electronically controlled 4L60E behind the LT1 is the drivetrain's weak point at high mileage. Common failures include valve-body wear (notably in the TCC/lockup PWM bore), a weak forward sprag, worn clutch packs, and the '3-4' clutch / sunshell. Symptoms range from harsh 1-2 shifts (ECU commanding max line pressure to mask bore wear) to failing to downshift into first at a stop, then bogging when pulling away.
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What does P1870 mean on Buick?▼
P1870 stands for "Transmission Component Slipping." This manufacturer-specific code (common on GM and Ford automatics, e.g. 4L60E) means the computer detected slippage between transmission components, most often at the torque converter clutch, where commanded engagement does not match actual behavior. When it sets, the PCM typically raises line pressure to protect the transmission and may lock out the converter clutch. Symptoms include harsh or delayed shifts, RPM flare/slipping, and reduced fuel economy. It often points to a worn valve body bore or TCC components and should be addressed before further internal damage occurs. On Buick specifically, this code is documented across 1 model.
What causes P1870 on Buick vehicles?▼
Common causes on Buick: Worn torque converter clutch (TCC) regulator valve bore in the valve body, Faulty TCC solenoid or PWM solenoid, Worn or failing torque converter clutch, Low or degraded transmission fluid, Worn internal clutches or seals (e.g., input shaft O-ring). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P1870 on a Buick?▼
Repair costs on Buick range from $1,500 to $3,000, depending on the specific model and root cause.
Which Buick models have P1870 documented?▼
Au7o has documented P1870 on 1 Buick model: Roadmaster.