P1860 on GMC: How to Diagnose & Fix
TCC PWM Solenoid Circuit Electrical
1 GMC model · 1 documented issue · 1 critical · $350-$4,500 repair
P1860 on GMC by model: symptoms, diagnosis and fix
The heavy-duty 4L80E (4L85E behind the 8.1L and the diesel) fitted to Savana 2500 and 3500 vans develops a distinct failure set from the 1500's 4L60E. Owners report shuddering around 45 mph as the torque converter clutch tries to lock, hard or late shifts, no downshift on throttle demand, and in advanced cases the van reaching operating temperature and then behaving as though it is in neutral in every gear. Root causes documented on 3500 vans include a failed TCC PWM solenoid or its electrical circuit, worn valve body bores, and pressure loss from a worn pump. Commercial-fleet duty cycles - constant loaded stop-and-go, cutaway upfit weight at the top of the GVWR - accelerate all of it.
Common Symptoms
- Shudder at approximately 45 mph
- Harsh or late upshifts
- No downshift when throttle is applied
- Neutral-like condition in all gears when hot
- Overdrive inoperative
- Check engine light with transmission codes
How to Fix
No recall. GM bulletin 08-07-30-001 covers 4L80E harsh/delayed shifts, slipping and no forward/reverse. Diagnose electrically first: a TCC PWM solenoid or its wiring is a comparatively cheap repair ($350-$700) and P1860 points straight at it. If pressure tests show pump or valve body wear, or the van has lost gears, the fix is a rebuild or reman unit at roughly $2,500-$4,500 installed for a 3500. On any van used as a work truck, fit an auxiliary cooler and service the fluid every 50,000 miles rather than following the severe-service book interval.
Sources for this issue (3)
P1860 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 P1860 mean on a GMC?
P1860 stands for "TCC PWM Solenoid Circuit Electrical." P1860 is a manufacturer-specific code (most commonly seen on GM vehicles such as Chevrolet, GMC, Buick, and Cadillac) indicating an electrical fault in the Torque Converter Clutch (TCC) Pulse Width Modulation (PWM) solenoid circuit. The PCM/TCM sets this code when it detects a continuous open, short to ground, or short to power in the TCC PWM solenoid valve circuit. This solenoid controls fluid flow that locks up the torque converter, so a fault can affect shift quality, cause stalling at stops, or trigger limp mode. On GMC it is documented across 1 model: Savana.
What are the most common causes of P1860?
The most common causes of P1860 are: Failed or shorted TCC PWM solenoid, Open, shorted, or corroded wiring in the solenoid circuit, Damaged or corroded transmission connector / internal wiring harness, Low or contaminated transmission fluid affecting solenoid operation, Faulty PCM/TCM or driver circuit, Internal transmission valve body / fluid passage problem. The specific cause varies by vehicle.
How much does it cost to fix P1860 on a GMC?
Published repair estimates on GMC range from $350 to $4,500 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.
Looking for P1860 on a different make?
View P1860 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.