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GTECH Calibration
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P1520

Gear Indicator System.

  • Cadillac
  • 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 a Cadillac, P1520 means the Gear Indicator System has a fault. The control unit has seen the gear position or gear indicator signal disagree with what it expects, or found a problem in the circuit that drives the gear display. The exact signal it monitors varies by model and transmission, so check the manufacturer data for your vehicle.

Symptoms

  • Gear selector display in the instrument cluster is wrong, blank or flickering
  • Malfunction indicator lamp or transmission warning lamp on
  • Gear position shown does not match the selector position
  • Possible harsh, delayed or odd shifting on some models
  • Starting problems or no-start in some positions on models where the selector position feeds the start circuit

Possible causes

  • Faulty or misadjusted transmission range switch (park/neutral or gear position switch)likely
  • Damaged wiring, corroded terminals or poor connections in the range switch or indicator circuitlikely
  • Selector linkage or cable out of adjustment, so the lever position does not match the transmissionpossible
  • Fault in the instrument cluster or gear indicator display circuitpossible
  • Fault in the transmission or powertrain control module, or an outdated calibrationrare
  • Internal transmission fault affecting the position signalrare

How to diagnose

  1. Read all stored codes and freeze frame data, and note whether other transmission or network codes are present
  2. Compare the selector lever position with the gear shown on the display in every range
  3. Check the selector linkage or cable for looseness, wear and correct adjustment
  4. Inspect the range switch wiring and connector for damage, water ingress, corrosion and bent pins
  5. Using the manufacturer's data, view the live gear position or range switch inputs and see whether they follow the lever through each position
  6. Check the range switch supply, ground and signal circuits for correct voltage and continuity
  7. Check the cluster and control module connectors and grounds, and look for any applicable software updates for your model
  8. Clear the code and road test to see if it returns

How to fix

  • Adjust the selector linkage or cable and re-set the range switch to the manufacturer's procedure
  • Replace a faulty transmission range switch
  • Repair damaged wiring and clean or replace corroded connectors
  • Repair or replace the instrument cluster if the display circuit is at fault
  • Update the control module calibration only if an outdated calibration is a known cause for your model
  • Diagnose and repair any internal transmission fault found

Can I keep driving?

Medium severity

The car can usually be driven short-term, but get it checked soon because a wrong range signal can affect shifting and starting. If it shifts harshly, will not select gears properly or shows a transmission warning, limit driving and have it inspected.

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

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