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P1850

Brake Band Apply Solenoid Circuit.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
8
AreaTransmission
50
FaultThe specific fault in that area

What it means

On Buick (GM) vehicles P1850 means the transmission control module has detected a fault in the brake band apply solenoid circuit. The module saw an electrical reading (open circuit, short to earth or short to voltage) that did not match what it expected when it commanded the solenoid. The exact solenoid and its location in the automatic transmission depend on the model and transmission type.

Symptoms

  • Malfunction indicator lamp or transmission warning lamp on
  • Harsh, delayed or flared gear changes
  • Transmission stuck in one gear or in a limp-home mode
  • Loss of engine braking or a particular gear range
  • Poor fuel economy or slipping under load

Possible causes

  • Damaged, chafed or corroded wiring between the transmission control module and the solenoidlikely
  • Poor connection or water or fluid contamination in the transmission harness connectorlikely
  • Faulty brake band apply solenoid (open or shorted coil)likely
  • Low or contaminated transmission fluid affecting the solenoid or valve bodypossible
  • Internal transmission wiring harness faultpossible
  • Faulty transmission control module or driver circuitrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting whether the fault is current or intermittent, and check for other transmission codes
  2. Check transmission fluid level and condition, looking for burnt smell, debris or discolouration
  3. Inspect the transmission harness and connectors for chafing, corrosion, bent pins, fluid ingress and heat damage
  4. Check battery condition and charging voltage, as low voltage can upset solenoid circuit monitoring
  5. Measure the solenoid coil resistance and compare with the manufacturer specification for that model and transmission
  6. Check the supply, control and earth wiring for continuity and for shorts to earth or voltage
  7. Operate the solenoid with a suitable scan tool active test, if supported, and listen or watch for a response
  8. Only after the wiring and solenoid are proven good, check the control module for faults and any applicable updates for that model

How to fix

  • Repair or replace damaged wiring and clean or replace corroded or contaminated connectors
  • Replace the faulty brake band apply solenoid, following the procedure for that transmission
  • Correct the fluid level or change the fluid and filter if it is contaminated or degraded
  • Replace the internal transmission harness if it is found faulty
  • Replace or reprogram the transmission control module only if testing confirms it is at fault and the manufacturer procedure calls for it

Can I keep driving?

Medium severity

The car can usually be driven short distances if it shifts normally, but get it checked soon. If it is in limp-home mode, slipping or shifting harshly, limit driving, as continued use can damage the transmission.

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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