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P0187 OBD-II Trouble Code: Fuel Temperature Sensor "B" Circuit Low Input

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P0187 trouble code definition

Fuel Temperature Sensor “B” Circuit Low Input

What the P0187 code means

The fuel temperature sensor detects the existence of fuel contamination (water, ethanol and dirt) inside the fuel tank, as well as monitoring the temperature of the fuel inside the fuel tank. The fuel temperature sensor will alert the Power Control Module (PCM) if the fuel temperature rises above or falls below the range that has been preset by the vehicle’s manufacturer.

When this happens, the Power Control Module (PCM) stores the P0187 trouble code. In some vehicles, the Check Engine Light may take longer to come on and will only light up after several failed cycles. In other vehicles, the Check Engine Light will come on immediately.

What causes the P0187 code?

In most cases, failure of the fuel pump is the cause of the P0187 trouble code. In other cases, the P0187 trouble code can be attributed to fuel temperature sensor wiring that is broken, damaged, or shorted. Another possible cause is a failed fuel temperature sensor. There could also be a problem with the Power Control Module (PCM), but this is very rare.

What are the symptoms of the P0187 code?

  • The Check Engine Light has illuminated.
  • The absence of symptoms is possible.
  • The car hesitates.
  • The car hesitates or stutters during acceleration.
  • The car will not start at all.
  • There are additional fuel system codes when scanned.

How does a mechanic diagnose the P0187 code?

To complete this diagnosis effectively, you will need to have an OBD-II scanner, a digital volt ohmmeter, and an oscilloscope.

  • Do a visual inspection of the wiring and connectors to the fuel temperature sensor. If necessary repair the wires, circuitry, and connectors.

  • Retrieve the freeze frame data and trouble codes that have been stored by the Power Control Module (PCM) using an OBD-II scanner.

  • Do a test drive after the codes have been cleared from the Power Control Module (PCM).

  • An intermittent problem may exist if the P0187 trouble code does not return immediately. This may prove to be difficult to diagnose as intermittent problem sometimes need to get worse before a diagnosis can be completed.

  • The reference voltage and ground signals will need to be checked with a digital volt ohmmeter at the connector of the fuel temperature sensor if the trouble code P0187 does return immediately.

  • If you do not get a voltage reading, check for continuity and resistance on the reference circuit using a digital volt ohmmeter.

  • If there are wires that are exposed or shorted, replace them as well as any necessary replacement of the connectors.

  • Test the continuity and resistance on the ground circuits, using an oscilloscope. This test result should coincide with the manufacturer’s specification.

  • With the presence of both a reference voltage and ground signal, use the oscilloscope to look at the waveform patterns on the fuel temperature sensor wire. Use live data to compare the waveform data with the manufacturer’s specifications.

  • When the contaminant content is high, the waveform frequency will be high as well. This determination can be made by comparing the levels of contamination in the fuel sensor waveform frequency with the actual fuel composition.

  • When the fuel temperature is high, the waveform pulse will be high as well. A determination as to the temperature of the fuel by comparing the waveform pulse width data.

  • If the collected data and the verified conditions do coincide, this is an indication that there may be a problem with the Power Control Module (PCM). This is not common.

  • If the collected data and the verified conditions do not coincide, the fuel temperature sensor will need to be replaced.

  • After replacing the fuel temperature sensor, test the fuel system to make sure the repair was successful.

Common mistakes when diagnosing the P0187 code

When diagnosing the P0187 trouble code, a common mistake is to determine that the fuel temperature sensor is faulty before considering the other components that may need to be repaired. The wires and grounds should be inspected before replacing the fuel temperature sensor.

How serious is the P0187 code?

When symptoms are present, the P0187 trouble code is considered a serious one. This code is known to cause drivability issues as well as preventing the car from starting.

When there are no symptoms, the P0187 trouble code would not be considered serious although it should be addressed immediately.

What repairs can fix the P0187 code?

  • Repairing damaged or broken fuel temperature sensor wires
  • Repairing faulty grounds
  • Repairing fuel temperature sensor connector corrosion
  • Replacing fuel pump
  • Replacing fuel temperature sensor
  • Reprogramming, updating, or replacing the power control module (PCM)

Additional comments for consideration regarding the P0187 code

It may be necessary to replace the fuel pump if the fuel temperature sensor is faulty. This will depend on the type of vehicle you have. It is common for the fuel temperature sensor to be built inside the fuel pump. If this is the case, it can be replaced independently. A complete diagnosis should still be done to minimize the likelihood of misdiagnosis.

It is important to note that flex fuel vehicles operate differently than others. They are able to operate with a greater amount of ethanol in its fuel and the fuel temperature sensor in these vehicles measure ethanol differently than the other fuel contaminants.

Need help with a P0187 code?

YourMechanic offers certified mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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