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Home >> GMC >> 2017 >> Acadia SL >> Repair and Diagnosis >> External Pages >> Different car >> Section 197 (Automatic Transmission - 8L45 (M5N M5T) Or 8L90 (M5U) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P1840, P1841, P18B9, P18BE, or P18C3: Internal Mode Switch S >> Circuit/System Verification

Circuit/System Verification

WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition On.
  2. Verify the range selector lever cable adjustment is correct. Refer to Range Selector Lever Cable Adjustment .
    • If the range selector lever cable adjustment is not OK 

      Adjust, repair or replace as necessary.

    • If the range selector lever cable adjustment is OK 
  3. Verify the scan tool the 9 V Reference 1 Circuit Status does not display Malfunction.
    • If Malfunction is displayed 

      Refer to Circuit/System Testing.

    • If Malfunction is not displayed 
  4. Verify the scan tool the internal mode switch A/B/C/P/S signal circuit voltages are correct for Park, Reverse, Neutral, Drive and Manual Mode position. Refer to Transmission Internal Mode Switch Voltage .
    • If the internal mode switch voltages are not OK 

      Refer to Circuit/System Testing.

    • If the internal mode switch voltages are OK 
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observe from the Freeze Frame/Failure Records data.
  6. Verify the DTC does not set.
    • If the DTC sets 

      Refer to Circuit/System Testing.

    • If the DTC does not set 
  7. All OK.
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