What is the meaning of a Nissan low coast brake solenoid valve or code P1774? What causes it, and how can you fix it?
Code P1774 is set by TCM when it detects a fault with the automatic transmission fluid (ATF) sensor or brake solenoid valve. The most common cause of this code is a short or open circuit in the wiring. It can trigger the check engine light, and gear shifting becomes problematic.
Read on for detailed information about what causes code P1774 and how to fix it.
What Is A Low Coast Brake Solenoid Valve Problem Or Code P1774 On Nissan?
When you get the P1774 code using an OBD2 scanner, there could be a mechanical or electrical fault with the low coast brake solenoid valve affecting car operation and drivability. It means that one of the solenoids aiding gear changing has a fault.
The P1774 code is set by the Transmission Control Module (TCM) when the Low Coast Brake Solenoid Valve fails to respond appropriately. TCM receives a signal from the Park and Neutral Position (PNP) switch, Throttle Position Sensor, and Vehicle Speed Sensor to open or close the solenoid valves. That’s how gear changing occurs in cars with automatic transmission systems.
As the driver, you will experience harsh gear shifting or the transmission system fails to change gear even if you push the gas pedal to the flow. There is an erratic operation that should tell you that something is wrong with your car. This type of fault significantly affects drivability.
Many people treat code P1774 as urgent, and we suggest that you do the same. You will not be happy with the drivability of your car. So, call your mechanic or take the vehicle to an auto repair shop at the first opportunity.
Is It Safe To Continue Driving With This Code?
You should fix the low coast brake solenoid valve problem as soon as possible. Driving your car with it may not be safe. Besides, it will take you much longer to get to your destination if the car switches to limp mode or is stuck in a lower gear. Treat it with the urgency it deserves.
What Causes The Low Coast Brake Solenoid Valve Problems Or Code P1774?
There are different causes of low coast brake solenoid valve faults. By definition, it is an electromechanical system. So, anything that tampers with wiring and mechanical components is enough to make it fail. The following are the common causes:
Damage to Wiring and/or Connector
Wires are the lifeline of any solenoid system, and the low coast brake solenoid valve is not different. A short or open circuit interferes with the electric current flow to energize the coil. Without that, the operation of the entire system fails.
Faulty Low Coast Brake Solenoid Valve
The valves themselves can fail to open or close for mechanical reasons. Energizing or de-energizing the coils does not guarantee that the rest of the components will function appropriately. But in many cases, the valve fails due to a short or open connection in the electrical circuit.
Faulty ATF Pressure Switch 2
An automatic transmission fluid (ATF) switch or sensor reads the amount of pressure within the transmission system. It then transmits the data to the car’s computer and determines if a gear change is necessary.
A faulty ATF switch will result in difficulty changing gears and may trigger the Check Engine Light. This is because of the wrong information that a malfunctioning device sends to the control module.
How Can I Diagnose This Code?
The first diagnostic for the P1774 code is a visual inspection. You should check the transmission harness or connectors for visible problems. Check if there are any broken connectors to the TCM. In case everything looks okay, find a compatible OBD2 diagnostic tool.
- Plug a scanner on the OBD2 port in your car, usually located under the dashboard on the driver’s side.
- Turn on the ignitions but don’t start the engine.
- Turn on the scanner and let it connect to the onboard computer. It will help you find the problem, if it is a faulty ATF pressure switch 2 or low coast brake solenoid valve.
The diagnosis process with an OBD2 scan tool may be challenging if you are not an advanced DIYer. If you don’t have the skills, contact your mechanic for help.
How Can I Fix The Low Coast Brake Solenoid Valve Problem?
The solution for low coast brake solenoid valve problems can also be time-consuming if it involves replacing components such as damaged wiring or faulty valves. What may be easy to figure out is the connection problem in the transmission wire harness. It only requires soldering back any broken connectors, and everything should be fine.
If you confirm that your ATF switch 2 is faulty, you need to replace it with a new one. Proceed as follows:
- Park your car on a flat surface, shift the gear to park mode, and raise it using a floor jack until the wheels are completely off the ground. Place the jack stands and lower the vehicle to rest on them. Ensure the car is stable.
- Install a 9-volt battery into the cigarette lighter socket to keep the car computer running. You can skip this step if you cannot access the required battery.
- Open the hood and disconnect the battery by unbolting the ground strap from the negative battery terminal. That will disable power going into the ATF switch and is necessary to prevent any fluid leaks. However, you still need to wear protective gloves, safety glasses, and oil-resistant clothes for the next step.
- Slide under the vehicle with the right tools for the job, such as a creeper and flashlight. Locate where the ATF switch is and remove any harness connected to it. If there is a bracket or other mounting hardware securing it to the transmission, you also need to remove it.
- Remove the ATF switch mounting bolts and use a flat-headed screwdriver to pry the switch off the transmission. Install a new one, and you are ready to test drive. Follow these steps in reverse.
Replacing the brake solenoid valve is not as straightforward as the ATF switch. It is a costly repair, especially if you have to replace the entire valve body. Your mechanic should help you go about it, or you can refer to this low coast brake solenoid valve fix thread for a DIY approach.
The P1774 is a rare problem in Nissan cars. But when it occurs, fix it as soon as possible. It tells you that the ATF switch or brake solenoid valve is acting up. Start by checking the wire harness for any short or open circuits. If everything is fine, use an OBD2 scanner to perform diagnostic and replace any faulty components.