OBD-II Code P0985 — What It Means & How to Fix It

What Does This Error Mean?

P0985 means Shift Solenoid F Control Circuit is Low. Solenoid F is used on 6-speed and higher automatic transmissions for specific gear combinations. A low circuit condition means the TCM detects a short to ground on the solenoid F control wire or a shorted solenoid coil. The gears controlled by solenoid F may not engage, causing skipped gear changes or limp mode operation.

Affected Models

Vehicles with 6-speed or higher automatic transmissions
Common in GM 6L80 and 6L90 transmissions in Silverado, Sierra, and Camaro
Common in Ford 6R80 transmissions in F-150 and Mustang
Common in Toyota A760 and A960 series 6-speed automatics

Common Causes

Shorted shift solenoid F coil with near-zero resistance to ground
Short to ground in the external solenoid F control wiring
Damaged internal transmission harness with a wire shorting to the transmission case
Corroded or contaminated external harness connector causing a partial short
Faulty TCM output driver circuit for solenoid F

How to Fix It

Disconnect the external transmission harness connector. Measure resistance between the solenoid F control wire and chassis ground.

A reading below 5 ohms indicates a short to ground. Identify whether the fault is in the external harness or inside the transmission.
Check the external harness for chafed, pinched, or burned wires. Look especially at areas where the harness contacts the transmission case or exhaust components.

Heat from the exhaust is a common cause of harness insulation failure on 6-speed transmissions in trucks and performance cars.
Drop the transmission pan and inspect the internal harness for shorts. Look for insulation damage where the harness routes past the valve body.

On GM 6L80 transmissions, the internal harness connector is a known wear point — inspect all wire entries at the connector body.
Test solenoid F directly. Disconnect it from the internal harness and measure resistance. Replace if near-zero ohms confirms an internal short.

Healthy solenoid resistance is typically 10 to 30 ohms. A shorted solenoid reads below 5 ohms.
Repair or replace the faulty component. Reinstall with new filter and ATF. Clear codes and confirm all 6 gear ranges shift correctly.

A 6-speed transmission should show smooth, sequential shifts without skipping gears during a full highway test drive.

When to Call a Professional

Solenoid F replacement with fluid service costs $300 to $600. Internal harness replacement adds $150 to $350. External wiring repair is $150 to $400. TCM replacement if needed runs $400 to $900.

Frequently Asked Questions

What does solenoid F control in a 6-speed?

In a 6-speed automatic, solenoid F is typically used in the higher gear combinations. The exact gear combinations vary by transmission — consult a shift chart for your specific transmission model. A fault in solenoid F usually affects 5th and/or 6th gear availability.

Can I still drive with P0985?

You may be able to drive in limp mode. However, the transmission will likely avoid the gears solenoid F controls. Highway driving is impractical — you will be stuck in a lower gear. Get it diagnosed soon.

Is a shorted solenoid common in high-mileage vehicles?

Yes — solenoid coils can develop internal shorts as insulation breaks down over time. High heat cycles and fluid contamination accelerate coil degradation. Regular ATF changes extend solenoid life significantly.