P0785 on GMC
Shift/Timing Solenoid "A" Malfunction
P0785 on GMC vehicles indicates shift/timing solenoid "a" malfunction. Au7o has documented this code across 1 GMC model — most commonly on Sierra 1500. This code indicates a malfunction in the shift/timing solenoid circuit, often associated with a solenoid (such as the 3-2 timing/downshift solenoid) that controls the timing and feel of gear changes. The transmission control module detected the solenoid is not performing as commanded electrically or hydraulically. Symptoms may include harsh or poorly timed shifts, particularly on downshifts, or a check engine light with otherwise normal driving. It generally indicates a transmission shift-control fault. Typical repair costs on GMC range from $1,800 to $3,500, depending on the specific model and root cause.
Common Causes of P0785
- •Faulty shift/timing solenoid
- •Low or contaminated transmission fluid
- •Wiring or connector damage in the solenoid circuit
- •Valve body debris or wear
- •Internal hydraulic leaks
- •Dirty transmission filter affecting solenoid response
- •Faulty transmission control module (less common)
P0785 on GMC by Model
GMC Sierra 1500(1 issue)
- 4L60-E / 4L65-E Sun Shell Failure Causing Loss of Reverse and 2nd/4th Gear2000-2007
On GMT800 Sierra 1500 trucks equipped with the 4L60-E family automatic, a well-known internal failure is cracking or stripping of the reaction sun shell. Owners commonly report sudden loss of reverse, no 2nd gear, no 4th gear, or a truck that starts in 3rd gear after a bang or flare. This is widely documented in transmission rebuild literature, repair databases, and owner reports for GM trucks and SUVs using this transmission.
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What does P0785 mean on GMC?▼
P0785 stands for "Shift/Timing Solenoid "A" Malfunction." This code indicates a malfunction in the shift/timing solenoid circuit, often associated with a solenoid (such as the 3-2 timing/downshift solenoid) that controls the timing and feel of gear changes. The transmission control module detected the solenoid is not performing as commanded electrically or hydraulically. Symptoms may include harsh or poorly timed shifts, particularly on downshifts, or a check engine light with otherwise normal driving. It generally indicates a transmission shift-control fault. On GMC specifically, this code is documented across 1 model.
What causes P0785 on GMC vehicles?▼
Common causes on GMC: Faulty shift/timing solenoid, Low or contaminated transmission fluid, Wiring or connector damage in the solenoid circuit, Valve body debris or wear, Internal hydraulic leaks. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0785 on a GMC?▼
Repair costs on GMC range from $1,800 to $3,500, depending on the specific model and root cause.
Which GMC models have P0785 documented?▼
Au7o has documented P0785 on 1 GMC model: Sierra 1500.