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P1842

1-2 Shift Solenoid Circuit Low Voltage.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
8
AreaTransmission
42
FaultThe specific fault in that area

What it means

P1842 on a Buick means the transmission control module has detected a low voltage in the 1-2 shift solenoid circuit. The module monitors the solenoid control circuit and sets the code when the voltage is lower than expected, which points to a short to ground, a wiring fault or a fault in the solenoid itself. The 1-2 shift solenoid controls the shift between first and second gear in the automatic transmission.

Symptoms

  • Malfunction indicator lamp or transmission warning lamp on
  • Harsh, delayed or missing 1-2 shift
  • Transmission stuck in one gear or in a limp-home mode
  • Poor acceleration from a standstill
  • Poor fuel economy
  • Possible flare or slipping between gears

Possible causes

  • Wiring to the 1-2 shift solenoid chafed or shorted to groundlikely
  • Faulty 1-2 shift solenoid with an internal short or low resistancelikely
  • Damaged or corroded connector or internal transmission harnesslikely
  • Fluid contamination or metal debris affecting the solenoid and wiring inside the transmissionpossible
  • Low or degraded transmission fluid affecting the solenoid and valve body operationpossible
  • Faulty transmission control module driver circuitrare

How to diagnose

  1. Read all stored codes and freeze frame data, then note whether the fault is current or intermittent
  2. Check the transmission fluid level and condition, looking for a burnt smell, dark colour or debris
  3. Inspect the external wiring and connector to the transmission for chafing, corrosion, water ingress and bent or pushed-back pins
  4. Check the wiring for continuity and for a short to ground between the control module and the transmission connector, following the wiring diagram for the model
  5. Measure the 1-2 shift solenoid resistance and compare it with the manufacturer specification for that transmission
  6. Check the solenoid supply voltage and control signal while operating the solenoid with a suitable scan tool function
  7. Inspect the internal harness and solenoid when the pan is removed, checking the pan for debris
  8. Check for updated software or technical bulletins for the model and transmission, as the procedure varies

How to fix

  • Repair or replace the damaged wiring or connector, sealing out any moisture
  • Replace the faulty 1-2 shift solenoid, or the solenoid pack if it is only supplied as an assembly
  • Replace the internal wiring harness if it is damaged
  • Correct the fluid level, or change the fluid and filter if it is contaminated, and rectify the cause of the debris
  • Replace or repair the transmission control module only after the wiring and solenoid are confirmed good

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but incorrect shifting or limp mode may stress the transmission. Get it checked soon to avoid further damage and an unsafe lack of drive.

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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