P0974 on Chevrolet: How to Diagnose & Fix
Shift Solenoid 'A' Control Circuit High
1 Chevrolet model · 1 documented issue · 1 critical · $300-$2,500 repair
P0974 on Chevrolet by model: symptoms, diagnosis and fix
Separate from the well-known torque converter shudder, the Allison 1000 in these trucks is documented for shift solenoid faults that drop the transmission into limp mode. The TCM sets P0700 - a generic 'transmission fault' pointer - accompanied by a specific code such as P0871 or P0872 (pressure switch E reading wrong for the commanded state of shift solenoid E, often caused by the solenoid or a sticking valve). When that code sets, the transmission falls to hydraulic default, the TCM inhibits torque converter clutch engagement, and the truck is left in a single gear, usually third, sometimes refusing to move at all until it is restarted. On a loaded 2500HD this strands the truck. Forum diagnosis repeatedly finds the cause outside the solenoid itself: low or burnt fluid, a loose battery ground, or a chafed harness behind the transmission.
Common Symptoms
- Transmission stuck in one gear (limp mode)
- Check engine light with P0700
- Harsh or no shifts
- Torque converter clutch will not lock up
- Truck will not move until restarted
- Service transmission message
How to Fix
Do not open the transmission on a P0700 alone - read the sub-code first. Check fluid level and condition, then inspect the internal wiring harness pass-through connector, the transmission harness where it routes behind the case, and the battery/chassis grounds, all documented causes of these codes. If the solenoid body is genuinely at fault, the internal control solenoid body and the internal harness are replaced with the pan down. Fluid and filter service on the Allison's real interval (much shorter for tow and plow duty) is the strongest prevention. No recall covers this.
Sources for this issue (5)
- Allison 1000 issues and limp mode - Chevy and GMC Duramax Diesel Forumforum
- Allison 5sp: Limp mode bad solenoid - DuramaxDiesels.comforum
- Allison Transmission P0700 Code Help - Chevy and GMC Duramax Diesel Forumforum
- Allison pressure switch codes - Transmission Digestarticle
- Allison 5sp: Codes set P0847 & P0872 - DuramaxDiesels.comforum
P0974 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0974 mean on a Chevrolet?
P0974 stands for "Shift Solenoid 'A' Control Circuit High." The shift solenoid 'A' control circuit voltage is above the expected range (too high / open or shorted to power). On Chevrolet it is documented across 1 model: Silverado 2500HD.
What are the most common causes of P0974?
The most common causes of P0974 are: Solenoid circuit open or shorted to voltage, Faulty shift solenoid A, Corroded/damaged connector, Internal TCM fault. The specific cause varies by vehicle.
How much does it cost to fix P0974 on a Chevrolet?
Published repair estimates on Chevrolet range from $300 to $2,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.