P1173 — Fuel Rail Sensor In-Range Low Failure

OBD2 code P1173 flags a problem with the fuel delivery and mixture control (fuel rail sensor in-range low failure). Short, gentle driving to a shop is usually possible. Common culprits: faulty fuel rail pressure sensor or wiring, contaminated or incorrect fuel, vacuum or intake leaks skewing the mixture.

For Ford vehicles

feedback a/f mixture control H02S21 or rotor calibration diesel

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution Drive with caution. Mixture and fuel-pressure faults can cause stalling, hesitation in traffic and — when severe — catalyst damage. Avoid long trips until diagnosed.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P1173 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the fuel delivery and mixture control for damage, corrosion, chafing or poor contact.
Subsystem check Measure fuel pressure at the rail and compare with factory specification at idle and under load.
Subsystem check Check short-term and long-term fuel trims in live data to see which way the mixture is off.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P1173 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1173 (parts and labor, USD, independent shop rates): Replace the fuel filter: $80–$200; Replace the pressure regulator or sensor: $150–$450; Replace the fuel pump: $400–$900; Clean or replace injectors: $200–$800. Overall, fixing P1173 usually costs between $80 and $900. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How much does it cost to fix P1173?

Replace the fuel filter — $80–$200; Replace the pressure regulator or sensor — $150–$450; Replace the fuel pump — $400–$900; Clean or replace injectors — $200–$800. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will P1173 clear itself?

Sometimes P1173 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What is the most common cause of P1173?

The most common causes are: faulty fuel rail pressure sensor or wiring, contaminated or incorrect fuel, vacuum or intake leaks skewing the mixture.

What are the symptoms of P1173?

Drivers most often notice: loss of power under load, increased fuel consumption, Check Engine Light on, hard starting or long cranking.

What does OBD2 code P1173 mean?

When your scan tool pulls code P1173, it means the engine control unit has detected that the fuel rail pressure signal has dropped below the acceptable minimum threshold. Officially this reads as "Fuel Rail Sensor In-Range Low Failure," and it falls under the powertrain category since it directly affects how the engine manages fuel delivery and combustion. The fuel rail sensor monitors system pressure and feeds that data back to the ECU, which uses it to calculate injector pulse width and maintain the proper air-fuel ratio.

The ECU doesn't just check fuel pressure once—it watches it continuously while the engine runs. If the sensor voltage or pressure reading stays below factory specifications for longer than the programmed number of drive cycles, the module logs P1173 and turns on the Check Engine light. The freeze frame snapshot saved alongside the code is particularly valuable; it captures engine RPM, load, temperature, and vehicle speed at the exact moment the fault occurred, giving you precise conditions to recreate during testing.

Fuel system faults like P1173 are not the kind of issue you want to ignore for long. While your car may still technically run, the underlying condition can cause drivability problems and, if left untreated, potentially damage emissions components like the catalytic converter.

Symptoms

The Check Engine light is illuminated on the dashboard
Noticeable loss of power, especially when accelerating under load
Fuel economy has dropped compared to normal
The engine cranks longer than usual before starting, or struggles to start
Idle feels rough and the car hesitates or stumbles during acceleration
In more severe cases, you may notice a strong fuel odor coming from the engine bay or tailpipe

Common Causes

A faulty fuel rail pressure sensor, or damage to its wiring harness or electrical connector
A defective fuel pressure regulator that cannot maintain system pressure
Clogged or leaking fuel injectors disrupting proper fuel delivery
Vacuum leaks or intake manifold gasket failures that throw off the air-fuel mixture
Contaminated, diluted, or otherwise incorrect fuel in the system
A failing fuel pump that cannot supply adequate volume or pressure to the rail

How to Diagnose P1173

Plug in an OBD2 scanner and confirm P1173 is stored in permanent memory. Record the freeze frame data—this tells you exactly what the engine was doing when the ECU first flagged the fault.
Check for any related diagnostic trouble codes. Secondary codes often point directly to the root cause, whether it's an electrical issue, a vacuum leak, or a fuel delivery problem. Also look up technical service bulletins for your specific make and model; manufacturers sometimes publish known fixes or software updates for recurring P0xxx codes.
Perform a visual inspection of the fuel rail sensor, its wiring harness, and the corresponding connector. Look for chafed wires, corroded pins, loose contacts, or any signs of heat damage that could produce a low signal.
Test fuel pressure at the rail using a gauge while the engine is running at idle and under load. Compare the readings against the manufacturer's specification for your vehicle—pressure that falls significantly short indicates a supply-side problem, while correct pressure with a faulty sensor reading suggests the sensor itself is bad.
Monitor short-term and long-term fuel trim values in the scanner's live data stream. Sustained high positive trim indicates a lean condition, which can accompany the low fuel rail sensor reading and help narrow down whether the issue is mechanical or electrical.
Clear the code, then drive the vehicle through a complete drive cycle that recreates the conditions captured in the freeze frame. If P1173 does not return, the problem may have been intermittent. If it comes back, you have a confirmed active fault that needs repair.

Repair Options and Costs

The right repair depends entirely on which component is actually responsible for the low fuel rail sensor reading. Here are typical parts-and-labor costs at an independent shop:

Fuel filter replacement: $80–$200
Fuel pressure regulator or fuel rail pressure sensor replacement: $150–$450
Fuel pump replacement (in-tank assembly): $400–$900
Fuel injector cleaning or replacement: $200–$800

Total Cost Summary

Your total bill for P1173 will likely fall somewhere between $80 and $900 depending on the underlying cause. The most expensive repair—replacing the fuel pump—is rarely the first thing to check. Most technicians start with visual inspections, fuel pressure testing, and freeze frame analysis to avoid unnecessary parts purchases.

Driving Safety Verdict

Caution is warranted. While the vehicle may still operate short distances, a fuel delivery or mixture control fault can cause sudden stalling, noticeable hesitation during acceleration, and—in severe or prolonged cases—damage to the catalytic converter from an overly rich fuel mixture. Do not plan long highway trips or rely on the car for critical transportation until the issue has been properly diagnosed and repaired.