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GTECH Calibration
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P1851

Brake Band Apply Solenoid Performance.

  • Cadillac
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
8
AreaTransmission
51
FaultThe specific fault in that area

What it means

P1851 on a Cadillac means the transmission control module has judged the brake band apply solenoid to be performing outside its expected range. The module commands the solenoid to apply the band and monitors the result, such as gear ratio, slip or pressure response. When what happens does not match what was commanded, the code is set. Which gear or band is involved depends on the model and transmission fitted.

Symptoms

  • Harsh, delayed or flared gear changes
  • Transmission slipping or engine speed rising without matching acceleration
  • Transmission stuck in one gear (limp mode)
  • Engine braking missing or weak when slowing down
  • Check engine or transmission warning light on
  • Poor fuel economy

Possible causes

  • Low, dirty or burnt transmission fluid reducing hydraulic pressurelikely
  • Sticking or worn brake band apply solenoid or blocked valve body passagelikely
  • Worn or burnt brake band, or leaking apply servo or sealspossible
  • Wiring or connector fault between the solenoid and the control module (chafing, corrosion, poor pin tension)possible
  • Blocked transmission filter or internal fluid leak causing low line pressurepossible
  • Faulty transmission control module or outdated softwarerare

How to diagnose

  1. Read all stored codes and freeze frame data, noting road speed, gear commanded, temperature and any other transmission codes
  2. Check transmission fluid level, condition and smell, following the correct procedure for the model, and look for leaks
  3. Inspect the transmission harness and connector for damage, corrosion, fluid contamination and loose pins
  4. Check the solenoid's electrical resistance against the manufacturer specification for that transmission
  5. Check battery condition and charging voltage, as low voltage can upset solenoid operation
  6. Monitor live data for gear ratio, slip and commanded versus actual gear during a road test
  7. Measure line pressure and apply pressure against specification where the model allows
  8. Check for applicable technical bulletins or calibration updates for the vehicle and transmission

How to fix

  • Correct the fluid level or change the fluid and filter using the specified type if it is contaminated or degraded
  • Repair or replace damaged wiring, connectors or terminals
  • Replace the faulty brake band apply solenoid, or clean or repair the valve body if it is sticking
  • Overhaul the transmission, replacing the band, servo or seals, if internal wear or leakage is confirmed
  • Update or replace the transmission control module only if a fault or outdated calibration is confirmed as the cause

Can I keep driving?

Medium severity

The car may be driven a short distance if it shifts reasonably, but get it checked soon. Continued slipping can quickly damage the transmission, so stop driving if it slips badly or goes into limp mode.

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

This code for other makes

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