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Home / DTC / P0785 — 3-2 Shift Solenoid Circuit Electrical

P0785 — 3-2 Shift Solenoid Circuit Electrical

Detailed page for trouble code P0785.

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Code

P0785

HUMMER P — Powertrain

3-2 Shift Solenoid Circuit Electrical

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring to the 3-2 shift solenoid
  • Poor or corroded connector or pin at solenoid or PCM
  • Faulty 3-2 shift solenoid (coil failure)
  • PCM shift solenoid driver failure
  • Blown fuse or poor battery/ground voltage
  • Internal transmission harness damage (chafing, corrosion)

Symptoms

  • Check Engine/Malfunction Indicator Lamp (MIL) illuminated
  • Harsh, delayed, or improper 3-to-2 downshift (or 2-to-3 upshift) behavior
  • Transmission may stay in a wrong gear or go into limp/diagnostic mode
  • Reduced drivability or hesitation during acceleration
  • Possible poor fuel economy or transmission slipping

What to check

  • Read and record freeze frame and all stored/ pending codes with scan tool
  • Perform a visual inspection of transmission wiring harness, connectors, and grounds
  • Verify battery voltage (should be ~12–14 V) and good chassis/engine grounds
  • Backprobe solenoid connector with scan tool commanded ON/OFF to observe operation
  • Measure solenoid coil resistance with connector disconnected
  • Check continuity between solenoid connector and PCM pin, and inspect for shorts to ground or battery

Signal parameters

  • Supply voltage to solenoid: typically battery voltage (~12 V) at feed circuit
  • PCM driver: usually a low-side switch to ground; commanded ON pulls solenoid to ground
  • Expected coil resistance: commonly in the range 6–40 ohms (vehicle-specific — consult service data)
  • Expected current when energized: typically 0.2–2 A depending on solenoid design
  • When commanded ON by PCM, voltage at solenoid control pin should switch from ~battery voltage (open) to near 0 V (ground) if low-side switching

Diagnostic algorithm

  1. Connect a professional scan tool, confirm P0785 is current or stored, and note freeze frame data and other transmission codes.
  2. Visually inspect solenoid connector, wiring, and transmission harness for damage, corrosion, water intrusion, or pin deformation. Repair obvious damage.
  3. With ignition ON (engine off), verify battery voltage at transmission solenoid power feed and check for good ground continuity to chassis/engine ground.
  4. Disconnect the solenoid connector and measure coil resistance across the solenoid pins. Compare to factory specification. If open or out-of-range, replace solenoid.
  5. Backprobe the solenoid harness at the connector and command the 3-2 solenoid ON/OFF with a scan tool while monitoring voltage/current. Confirm the PCM changes the control circuit as expected.
  6. If the PCM does not command the circuit or the circuit does not switch correctly, check continuity between the solenoid connector and the PCM driver pin. Inspect for shorts to battery or ground.
  7. If wiring and connector integrity are verified and the solenoid bench test is good, suspect PCM driver fault. Confirm with a known-good PCM or follow manufacturer-specific PCM testing procedures before replacement.
  8. After repair (wire repair, connector replacement, solenoid replacement, or PCM repair), clear codes and perform a road test to verify normal shift operation and that the code does not return.

Likely causes

  • Corroded or disconnected connector at the solenoid
  • Open or shorted wiring between solenoid and PCM
  • Failed solenoid coil
  • Poor ground or low battery supply to transmission solenoids

Fault status

⚠️ Status
P0785 — 3-2 Shift Solenoid Circuit Electrical. Stored when the PCM detects an electrical fault (open/short/high/low current or intermittent) in the 3-2 shift solenoid circuit.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours
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