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GTECH Calibration
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P1823

Internal Mode Switch Circuit P Low.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
8
AreaTransmission
23
FaultThe specific fault in that area

What it means

On Buick models P1823 means the transmission control module has detected a low signal on the 'P' circuit of the internal mode switch (the transmission range switch inside the gearbox). The switch tells the control unit which gear position is selected. The code sets when the P input reads a voltage or state that does not match the other switch inputs or the expected pattern for the lever position.

Symptoms

  • Malfunction indicator or transmission warning light on
  • Engine will not start in Park or Neutral, or starts in other gear positions
  • Gear indicator on the dash shows the wrong position or flickers
  • Harsh, delayed or incorrect gear engagement
  • Transmission stuck in one gear (limp mode)
  • Reversing lights or cruise control behaving oddly

Possible causes

  • Internal mode switch (range switch) worn, dirty or out of adjustmentlikely
  • Damaged wiring or chafed harness between the switch and the control module, shorted to groundlikely
  • Corroded or loose connector at the transmission or control modulepossible
  • Gear selector cable or linkage out of adjustment so the switch is not aligned with the lever positionpossible
  • Contaminated or low transmission fluid affecting the switch contactspossible
  • Faulty transmission control modulerare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, including gear position and vehicle speed at the time of setting
  2. Compare the scan tool gear position display with the actual lever position in each range and see which inputs disagree
  3. Check the transmission fluid level and condition against the manufacturer's procedure
  4. Inspect the harness and connectors at the transmission and control module for chafing, water ingress, corrosion and bent pins
  5. Check the selector cable and linkage adjustment and the lever alignment with the switch
  6. Wiggle test the harness with the scan tool live data open to look for dropouts in the P signal
  7. Measure the switch circuit resistance and voltage against the model-specific wiring diagram, checking for a short to ground
  8. Confirm the switch and control module supply and ground are good before condemning any component

How to fix

  • Repair or replace the damaged section of wiring, or replace the harness if the insulation has failed
  • Clean or replace the affected connector terminals
  • Adjust or replace the selector cable and linkage so the switch aligns with each position
  • Replace the internal mode switch, adjusting as per the model-specific procedure
  • Correct the fluid level or change contaminated fluid with the specified type
  • Replace or reprogram the control module only after all wiring and switch faults have been ruled out

Can I keep driving?

Medium severity

The car can usually be driven short distances, but it may refuse to start, shift poorly or go into limp mode without warning. Get it checked soon to avoid being stranded or causing extra gearbox wear.

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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