Code Definition

P1842 — 1-2 Shift Solenoid circuit low input

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: GM

About P1842

P1842 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1842 is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1842 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This DTC sets when the Transmission Control Module (TCM) detects that the voltage on the 1 to 2 shift solenoid control circuit is persistently low, typically near 0V, indicating a possible short to ground or an internal solenoid fault. The 1 to 2 shift solenoid controls hydraulic flow for the first to second gear upshift. A low control circuit signal prevents proper solenoid actuation, which can cause harsh or incorrect shifts, failure to upshift, or the transmission defaulting to a fail safe gear. The fault is usually in the solenoid winding, its control wiring, or the TCM driver.

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