Selector cable or linkage out of adjustment, so the internal mode switch is not aligned with the selected gear; Worn or faulty internal mode switch (range switch) contacts; Damaged wiring, chafed insulation or corroded terminals in the switch circuits; Poor connection at the transmission harness connector, including water or fluid ingress; Loose or incorrectly fitted switch after previous transmission work; Fault in the transmission control module.

P1825

Internal Mode Switch Illegal Range.

Cadillac
Powertrain
Manufacturer code
Medium severity

How this code is built

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

What it means

On Cadillac models P1825 means the transmission control module has seen an illegal combination of signals from the internal mode switch, also called the transmission range or park/neutral position switch. The switch reports the selector position as a set of input signals, and the module saw a pattern that does not match any valid gear position. The exact switch design and circuit layout depend on the model and transmission.

Symptoms

Malfunction indicator lamp or transmission warning lamp on
Gear position shown on the dash does not match the selector
Harsh, delayed or erratic shifts
Transmission stuck in one gear or in a limp-home mode
Engine will not start in Park or Neutral, or starts in other gear positions
Reverse lamps not working correctly

Possible causes

Selector cable or linkage out of adjustment, so the internal mode switch is not aligned with the selected gearlikely
Worn or faulty internal mode switch (range switch) contactslikely
Damaged wiring, chafed insulation or corroded terminals in the switch circuitspossible
Poor connection at the transmission harness connector, including water or fluid ingresspossible
Loose or incorrectly fitted switch after previous transmission workpossible
Fault in the transmission control modulerare

How to diagnose

Read all stored codes and freeze frame data, noting whether other transmission or range-related codes are present
Check that the gear position shown on the scan data matches the selector position in each range
Inspect the selector cable, linkage and mounting for wear, damage or incorrect adjustment
Inspect the transmission harness and connector for chafing, corrosion, bent pins, fluid or water contamination
Check the transmission fluid level and condition, as contamination can affect the switch
Monitor the individual switch input states while moving the selector through each position and compare with the manufacturer's specification for that model
Check the switch circuits for continuity, short circuits and voltage drop, following the wiring diagram for the vehicle
Check the switch mounting and alignment against the specified procedure for the transmission

How to fix

Adjust or replace the selector cable or linkage and set the switch alignment to specification
Replace the internal mode switch if its signals are incorrect in any position
Repair damaged wiring and clean or replace corroded or damaged connector terminals
Refit or realign the switch correctly if it is loose or misplaced
Replace or reprogram the transmission control module only after the wiring and switch have been proven good, and only if a fault is confirmed

Can I keep driving?

Medium severity

The car can usually be driven short distances, but shifting may be poor or the transmission may enter a limp mode, so get it checked soon. Avoid driving if it will not start reliably, or if the gear position is uncertain or the transmission is not engaging properly.

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