P1826
Internal Mode Switch C Circuit High Voltage
What it means
P1826. Internal Mode Switch C Circuit High Voltage. This Chevy-enhanced code applies to Impala, Malibu, Monte Carlo, Silverado, Sierra.
Findings, check these first
- Faulty internal mode switch inside the transmission
- Open in IMS signal C circuit between PCM or TCM and the switch
- Misadjusted shift cable holding the switch between detents
- Corroded AT inline 20-way connector
- Faulty control module IMS input
Standard procedure
- Observe IMS A/B/C/P parameters in each shifter detent with a Tech2 scan tool
- Verify shift cable adjustment before opening the transmission
- Test IMS signal C circuit for opens and high resistance
- Jumper the signal circuit to ground and confirm the scan tool reads LOW
- Replace the internal mode switch if circuits and adjustment test normal
Look up another code
Press / to jump to the box. Chevy-enhanced powertrain, body, chassis and network codes.
Sources and review
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Last updated 2026-09-13.
Report a correction for P1826. Include your vehicle, the issue and a source if you have one.