What does it mean?
P1774 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Low Coast Brake Solenoid Valve Function . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- MIL (check engine lamp) is on and the transmission may enter limp mode
- No engine braking when the driver lifts off or manually selects a lower gear
- The vehicle freewheels downhill in manual low instead of holding back
- Delayed or harsh engagement when a low range is selected
- Shift quality changes markedly once the fluid is hot
- Slipping under load in the lower ranges
Likely causes
- Varnish or debris holding the coast brake solenoid valve so it cannot fully stroke
- Solenoid winding resistance drifting out of specification, weakening the valve action
- Worn valve body bore in the coast brake circuit, so the applied pressure bleeds off
- Worn coast brake band or clutch element, or hardened seals leaking under pressure
- Low fluid level, degraded fluid or a partly clogged filter reducing available pressure
- Corroded case connector or a high-resistance joint in the solenoid circuit
- Control module output driver weakening under heat
How to fix it
- Check the fluid level, colour and smell; renew the fluid and filter if it is dark or full of debris
- On a road test, compare commanded gear and slip in live data while lifting off in a manual low range
- Measure the solenoid winding resistance at the case connector and check for a short to the case
- Fit a pressure gauge and run a line pressure test in each range, paying attention to manual low
- Remove and inspect the valve body for stuck valves and worn bores; clean or replace as required
- If pressures are correct and the solenoid checks out, the coast brake element itself is worn and needs internal repair