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DTC codes / P01xx · Fuel and air metering / P01A5

P01A5Alternative Fuel Rail Pressure Sensor Circuit Low

P01A5 indicates that the powertrain control module (PCM) has detected a low-voltage signal from the alternative fuel rail pressure sensor circuit, which monitors the pressure of the alternative fuel (such as compressed natural gas or ethanol) in the fuel rail. The PCM compares the sensor's output to expected values and sets this code when the signal falls below the calibrated minimum for a specified time, indicating a short to ground, an open circuit, or a faulty sensor.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard
  • Often no symptoms besides the warning light, especially if the vehicle runs on gasoline as a backup
  • Rough idle or hesitation when operating on the alternative fuel
  • Reduced engine performance or power loss under load
  • Difficulty starting or stalling when running on the alternative fuel
  • Poor fuel economy or increased alternative fuel consumption

Common causes, most likely first

  1. Faulty alternative fuel rail pressure sensor
  2. Damaged or corroded wiring harness or connector at the sensor
  3. Short to ground in the sensor signal circuit
  4. Open circuit in the sensor reference voltage or ground circuit
  5. Low alternative fuel pressure due to a weak pump, clogged filter, or empty tank
  6. Contaminated or degraded alternative fuel affecting sensor readings
  7. PCM internal fault (rare)

How to diagnose and fix it

  1. Verify the alternative fuel level and condition; refill or replace fuel if contaminated
  2. Inspect the sensor and its connector for physical damage, corrosion, or loose pins
  3. Perform a visual inspection of the wiring harness for chafing, breaks, or shorts
  4. Use a digital multimeter to check sensor reference voltage (typically 5V) and ground continuity
  5. Measure the sensor signal voltage and compare to manufacturer specifications; replace sensor if out of range
  6. Check fuel rail pressure with a mechanical gauge to confirm actual low pressure versus sensor error
  7. If all electrical and mechanical checks pass, diagnose the PCM for internal faults

When the sensor is not the culprit

  • A low alternative fuel level or a failing fuel pump can cause the sensor to read low pressure even when the sensor itself is good, so always verify actual fuel pressure before replacing parts.
  • The code may set only when the vehicle is running on the alternative fuel, so intermittent symptoms can be missed if the vehicle is primarily operated on gasoline.
  • Corrosion inside the sensor connector is a common cause that is often overlooked during visual inspection, especially in regions with high humidity or road salt.
  • A short to ground in the signal circuit can be caused by a pinched wire behind the engine block or near the fuel rail, which may not be obvious without wiggling the harness while monitoring live data.
  • Replacing the sensor without checking the reference voltage can lead to repeat failures if the PCM is not supplying the correct 5V reference.

Can I keep driving with P01A5?

If the vehicle runs normally on gasoline, you can drive it to a repair shop, but avoid using the alternative fuel mode to prevent potential stalling or poor performance. If the engine runs rough or stalls on the alternative fuel, limit driving and seek service promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage