Power steering preo sensor circuit range/performance FOR A 2000 neon

code po551 refers to power steering pressure(PSP) sensor/ switch--range /performance problem===causes --PS system--PSP sensor/switch
Have the power steering pressure checked as it may be a pump problem or just the sensor/switch.. Check the reservoir level as it may be lacking fluid.

P0551 Power Steering Pressure Sensor/Switch Circuit Range/Performance

P0551 is for the power steering pressure switch. This is a switch that is threaded into the back of the steering rack. It's job is to tell the engine controller when pressure increases in the system from turning the wheel at low speeds, and the engine controller can increase the idle speed slightly to compensate. It's not incommon for these switches to fail.

You'll have to get at it from underneath the car. Look on the back of the steering rack and find the only electrical part on it, that's the switch you are after. Unplug it and check for signs of fluid leakage into the connector. Very often when they fail they will leak into the connector. This code setting is almost always the switch, but if you find fluid in the connector it's bad for sure.

This switch probably is a dealer item, but there should still be plenty of them around. Did you give Auto Zone a try? Or visit Rockauto.com, with this sample IMAGE LINK...

Hope helps.

P0551 power steering pressure sensor circuit range performance, this sensor idles up the RPM as steering wheel is turn in order to maintain proper idle and to prevent vehicle from stalling

The P1684 code simply means that the battery has been disconneted within the last 50 starts.
P0551(power steering pressure switch)

code po551 is power steering pressure switch circuit failure.

go to the dealer and get part

CODE PO551 -POWER STEERING PRESSURE SWITCH CIRCUIT FAILURE. CODE P1684 - BATTERY HAS BEEN DISCONNECTED.

P0551 Power Steering Pressure Sensor Circuit Range/Performance
There is a switch that senses the pressure of the hydraulic fluid which reflects how hard it is working (e.g. like when turning at low speed or when stopped). It then opens the switch (which is normally grounded) and a wire to the powertrain controller senses that and increase the idle speed accordingly so the engine doesn' falter. Here is an exchange I had earlier with another owner about it.
"The switch is located on the back side of the power steering gear. It is supposed to raise the idle speed when you are turning the wheels at low speeds when the system will require more pressure and thus otherwise drag down the idle. The wire to the switch is dark blue/light green (signal) and a black ground; and the signal wire goes to pin 45 of the powertrain control module. So you might check the connector at the switch and the connection to pin 45 of the controller, from pin 2 of the plug...
All I can add is that if you locate the two high pressure lines that run to the steering gear from the power steering pump you will find the switch right next to where those two lines connect to the gear. It no doubt just screws out and then install the new one. The manual says that you remove the electrical plug, lifting the locking tab carefully. Then it says to use a crowfoot wrench and extension to remove the old one. The steering fluid will run out so be prepared to clean catch it, and be ready to screw in the new one to minimize loss. If you catch the fluid in a clean pan you car reuse it. The torque spec with a crowfoot wrench is 12 foot pounds and you have to be careful not to exceed the limit or you may ruin the fine hydraulic threads on the steering gear and then you have a potentially expensive problem. So if you can't get a crowfoot that fits the sensor (when you buy the replacement you can see what the size it) and don't have an extension and a torque wrench you may want to let the shop do it. Make sure the electrical plug is in place with the locking tab engaging the tab on the switch. Refill the power steering reservoir. Start the engine and then turn the steering wheel from lock to lock several times to bleed the air from the system. Use only Chrysler power steering fluid if you loose some of it."
I doubt it has anything to do with the fluid, unless the code started right after that. If the wire seems OK, then the question is the switch stuck open (measure that) or is the pressure really too high when you are driving at normal speed or not even turning the wheel. That would have to measured with a gauge. Let me know what you learn, please, or have further questions. Hope this helps I know alot of info but should help you please rate thank you