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GTECH Calibration
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P1850

Brake Band Apply Solenoid Circuit.

  • GM
  • 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 GM vehicles, P1850 means the transmission control module has detected a fault in the brake band apply solenoid circuit. The module sees a voltage or current reading from the solenoid circuit that does not match what it commanded, such as an open circuit, a short to earth or a short to voltage. Which solenoid and band this relates to depends on the transmission and model.

Symptoms

  • Malfunction indicator lamp or transmission warning lamp on
  • Harsh, delayed or flared gear changes
  • Transmission stuck in one gear (limp mode)
  • Loss of engine braking or a missing gear range
  • Poor fuel economy

Possible causes

  • Faulty brake band apply solenoid (open or shorted coil)likely
  • Damaged, chafed or corroded wiring between the solenoid and the control modulelikely
  • Poor connection or water ingress at the transmission internal harness or external connectorlikely
  • Contaminated, degraded or low transmission fluid affecting the solenoid and valve bodypossible
  • Sticking valve body components or a worn band affecting apply pressurepossible
  • Fault within the transmission control module driver circuitrare

How to diagnose

  1. Read all stored and pending codes and record the freeze frame data, noting when the fault set and under what conditions
  2. Check the transmission fluid level, condition and smell, and look for leaks, as the correct procedure varies by model
  3. Inspect the external transmission connector and wiring for damage, corrosion, moisture and pushed-back pins
  4. Check the battery and charging voltage, as low supply voltage can cause circuit faults
  5. With the connector disconnected, measure the solenoid coil resistance and compare it with the manufacturer specification for that transmission
  6. Test the circuit wiring for continuity, short to earth and short to voltage between the solenoid and the control module
  7. Check the solenoid command and operation using a scan tool's output tests, where the model supports it
  8. Check for relevant technical service bulletins or calibration updates for the specific transmission and model

How to fix

  • Replace the brake band apply solenoid if its resistance or operation is out of specification
  • Repair or replace damaged wiring, terminals or the internal transmission harness
  • Clean and secure connectors, and seal out any water ingress
  • Change the transmission fluid and filter using the correct specification if it is contaminated or degraded
  • Repair or overhaul the valve body or band if the solenoid and wiring prove sound but the transmission still fails to apply correctly
  • Update or replace the transmission control module only after all other causes are ruled out, or if an outdated calibration is a known cause for that model

Can I keep driving?

Medium severity

The car can usually be driven carefully a short distance, but it may be in limp mode with harsh or missing gears. Get it checked soon, as continued driving can cause further transmission damage.

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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