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P0784 — 4 5 Shift

Generic OBD-II · all makesPowertrain (engine & transmission)

P0784 signals that the transmission control module has detected insufficient hydraulic pressure during the 4th to 5th gear shift.

Symptoms

What causes it — most likely first

1. Low or contaminated transmission fluid

Insufficient fluid level or dirty fluid reduces hydraulic pressure and is the most common trigger.

2. Faulty shift solenoid B

A failed solenoid can prevent the required pressure build‑up for the 4‑5 shift.

3. Worn or obstructed valve body passages

Internal blockage or wear in the valve body restricts fluid flow to the shift circuit.

4. Damaged wiring or connector to the solenoid

Corroded or broken wires/connector pins interrupt the control signal to the solenoid.

5. Transmission control module (PCM) issue

PCM failure is rare; it typically occurs only after other mechanical or electrical causes have been ruled out.

How it's diagnosed

  1. Check transmission fluid level and condition; top off or replace if low/dirty.
  2. Inspect wiring and connector for the shift solenoid B for corrosion, damage, or loose pins.
  3. Test shift solenoid B operation with a multimeter or scan tool.
  4. Monitor live transmission data for pressure values during shift attempts.
  5. Perform a hydraulic pressure test of the 4‑5 shift circuit.
  6. If pressure is still low, inspect valve body or replace the shift solenoid as needed.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0780 — Shift ErrorP0781 — 1 2 ShiftP0782 — 2 3 ShiftP0783 — 3 4 ShiftP0785 — Shift Timing SolenoidP0786 — Shift Timing Solenoid Rangeperformance

Frequently asked

Will replacing the PCM fix P0784?

Usually not; PCM failure is uncommon and should be considered only after fluid, solenoid, and mechanical checks have been completed.

Can I continue driving with this code?

It is not advisable; the transmission may shift harshly or slip, and prolonged operation can cause further damage.

How often does low fluid cause P0784?

Low or degraded fluid is the most frequent cause, especially in vehicles that have not had a fluid change in a long time.

Is a valve‑body replacement ever needed?

Only when internal passages are confirmed blocked or worn after other causes have been ruled out.