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DTC codes / P01xx · Fuel and air metering / P01B7

P01B7Alternative Fuel Rail Temperature Sensor Circuit High

P01B7 indicates that the powertrain control module has detected an abnormally high voltage signal from the alternative fuel rail temperature sensor circuit, which typically means the sensor is reading colder than actual or the circuit is open. The computer expects the sensor voltage to stay within a calibrated range, and a sustained high value sets this code.

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

Symptoms you may notice

  • Illumination of the malfunction indicator lamp, often with no other noticeable symptoms
  • Rough running or hesitation when the engine is cold, especially on alternative fuel such as compressed natural gas or propane
  • Poor fuel economy or altered fuel trim as the module substitutes a default temperature value
  • Hard starting or extended crank time in cold ambient conditions
  • In rare cases, a no-start condition if the module cannot establish a plausible fuel rail temperature
  • Possible reduced power or limp-home mode if the fault affects fuel delivery calculations

Common causes, most likely first

  1. Open circuit in the signal wire between the sensor and the powertrain control module
  2. Failed alternative fuel rail temperature sensor, typically an open thermistor element
  3. Corroded, loose, or disconnected electrical connector at the sensor or module
  4. High resistance in the ground circuit for the sensor
  5. Damaged wiring harness caused by chafing, heat, or rodent damage
  6. Internal fault in the powertrain control module, though this is uncommon
  7. Aftermarket or incorrect sensor installed that does not match the module calibration

How to diagnose and fix it

  1. Connect a scan tool and record the freeze-frame data and sensor voltage to confirm the high reading
  2. Visually inspect the sensor connector and wiring for corrosion, looseness, or obvious damage
  3. Measure the sensor resistance with a multimeter and compare it to the manufacturer's temperature-resistance chart
  4. Back-probe the signal circuit at the module and check for an open or high-resistance condition
  5. Check the ground circuit for excessive resistance using a voltage drop test
  6. Repair or replace the faulty wiring, connector, or sensor as indicated by the tests
  7. Clear the diagnostic trouble codes and verify the repair by running the appropriate monitor to confirm the sensor voltage returns to normal

What a high reading really tells you

  • A high voltage on a temperature sensor circuit almost always means an open circuit or a sensor with excessive resistance, not a sensor that is reading too hot.
  • Technicians often replace the sensor first, but a corroded connector or chafed wire is just as common and costs far less to fix.
  • The alternative fuel rail temperature sensor is sometimes shared with the fuel composition sensor on flex-fuel vehicles, so a fault in that shared circuit can set this code.
  • If the vehicle runs fine and the only symptom is the warning light, the module may be using a default temperature strategy that masks the fault until cold-start conditions expose it.
  • A poor ground connection at the engine block can raise the voltage seen on the signal wire and mimic a failed sensor, so always verify ground integrity before condemning parts.

Can I keep driving with P01B7?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy load, towing, or cold-start conditions because the module may be using an inaccurate fuel rail temperature and could deliver incorrect fuel mixture. If the engine runs rough or stalls, stop driving and have the fault diagnosed 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.

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