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GTECH Calibration
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P1520

Gear Indicator System.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
5
AreaVehicle speed, idle control and auxiliary inputs
20
FaultThe specific fault in that area

What it means

On Buick, P1520 is defined as a Gear Indicator System fault. The control unit has detected a problem with the gear position indicator circuit or the signal it uses to show the selected gear or range. The exact monitoring logic and which module sets it vary by model and transmission, so confirm against the vehicle-specific data.

Symptoms

  • Gear position display in the instrument cluster is wrong, blank or flickering
  • Malfunction indicator lamp or a transmission warning lamp is on
  • Display does not match the actual selector position
  • Possible starting problems or odd shift behaviour on some models, depending on how the range signal is used
  • Fault stored with no other obvious drivability complaint

Possible causes

  • Faulty or misadjusted transmission range switch / park-neutral position switch or selector position sensorlikely
  • Damaged wiring, chafing or corrosion in the range switch or indicator circuitlikely
  • Poor connection or water ingress at the transmission or switch connectorpossible
  • Worn or disconnected shift linkage or selector cable causing the selector and switch to disagreepossible
  • Fault in the instrument cluster or indicator driverpossible
  • Fault in the powertrain or transmission control module, or outdated software where a known update existsrare

How to diagnose

  1. Read all stored codes and freeze frame data, noting whether other transmission or network codes are present
  2. Check that the displayed gear matches the selector position in every range and note when it goes wrong
  3. Inspect the selector, linkage or cable for looseness, wear and correct adjustment
  4. Inspect the range switch wiring and connectors for damage, corrosion, moisture and bent or pushed-back pins
  5. View live data for the range switch or selector position and compare with the actual lever position
  6. Check the switch circuits for supply, ground and signal and for shorts or open circuits using the manufacturer wiring diagram for your model
  7. Test or swap-check the switch against the manufacturer specification, and check the instrument cluster operation
  8. Check for applicable software updates or service bulletins for the specific model and transmission

How to fix

  • Repair or replace damaged wiring and clean or replace corroded connectors
  • Adjust or replace the transmission range switch or selector position sensor and set it to specification
  • Repair or adjust worn shift linkage or selector cable
  • Repair or replace the instrument cluster if the indicator itself is faulty
  • Update the control module software only if a known fault requires it, or repair or replace the module after confirming the fault

Can I keep driving?

Medium severity

The car can usually be driven for a short time if it starts and shifts normally, but get it checked soon. If it will not start reliably, shifts erratically or the selector position is uncertain, limit driving until it is repaired.

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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