P0551 code meaning
Power Steering Pressure Sensor/Switch Circuit Range/Performance
What P0551 means
Hydraulic power steering has a pressure switch or sensor on the high-pressure line; when the wheel is turned at standstill, pump pressure and engine load rise sharply, so the engine module raises idle air in advance to stop the engine stalling. That makes it an input to idle control under CARB. Switches (Saab, Mitsubishi) ground a pull-up; analogue 5 V sensors (Toyota) give about 0.45 V at zero pressure. GM's and Ford's tables do not use P0550–P0554. P0551 means the switch reports high pressure where that is implausible – at speed there is hardly any steering. Mitsubishi sets it when the switch stays on through 10 drive-and-stop cycles; Saab's Trionic T8 after 600 s above 50 km/h, keeping raised idle as substitute and without warning lamp.
P0551 at a glance
- Check engine lightUsually not
- Emissions testCan fail
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0551
- Permanently slightly raised idle
- No load compensation when steering
- Check engine light depending on the maker (Saab: none)
Common causes of P0551
- Most likelyPressure switch stuck closed or faulty internally
- PossibleSignal line shorted to ground (ground means active)
- Less likelyPermanently high pressure (steering valve sticking, kinked line)
- Less likelyVehicle speed signal faulty (Saab depends on P0501)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Power steering pressure switchSensor wiringEngine control module
What each part of P0551 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 51 | The exact fault in that area. |
What to do next
- Note P0551 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0551
What does P0551 mean?
P0551 means "Power Steering Pressure Sensor/Switch Circuit Range/Performance". Hydraulic power steering has a pressure switch or sensor on the high-pressure line; when the wheel is turned at standstill, pump pressure and engine load rise sharply, so the engine module raises idle air in advance to stop the engine stalling. It is a generic code, so it means the same on every make.
Is it safe to drive with P0551?
Drive gently and only to a workshop. With P0551 the car can go into limp mode (reduced power) to protect itself.
Will P0551 fail an emissions test?
Yes, it can. P0551 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0551 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0551 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.