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P0189 OBD-II Trouble Code: Fuel Temperature Sensor "B" Circuit Intermittent

Check Engine Light

P0189 trouble code definition

Fuel Temperature Sensor “B” Circuit Intermittent

What the P0189 code means

The purpose of the fuel temperature sensor is to monitor the temperature of the fuel inside the fuel tank and send this information to the Power Control Module (PCM).

It also monitors the fuel for possible contamination of water, ethanol, or dirt. If the temperature of the fuel is not in the appropriate range, the fuel temperature sensor will send a signal to alert the Power Control Module (PCM) of the error.

The Power Control Module (PCM) will store the P0189 trouble code. The Check Engine Light will come one immediately for some vehicles, it will take longer for the Check Engine Light to come on for other vehicles.

What causes the P0189 code?

  • The fuel temperature sensor has failed
  • Wiring that is broken, exposed, or damaged
  • Fuel temperature sensor connector that is broken or corroded
  • Bad fuel pump
  • Power Control Module (PCM) that has broken or needs an update

What are the symptoms of the P0189 code?

  • There may be no symptoms at all
  • Check Engine Light has come on
  • Engine misfire
  • Car hesitates at times
  • Car hesitates upon acceleration
  • Car will not start up
  • Multiple fuel system trouble codes

How does a mechanic diagnose the P0189 code?

  • Inspects all wiring that leads to the sensor and connector, looking for wires that are burned or those that may have shorted out. If it is necessary, they will replace damaged circuitry and/or connectors.

  • Uses an OBD-II scanner to retrieve all trouble codes that have been stored by the Power Control Module (PCM) as well as any freeze frame data.

  • Clears codes and performs a test drive of the vehicle. The P0189 trouble code may or may not come back immediately.

  • If the P0189 trouble code does not come back, this is an indication that there is an intermittent problem. Intermittent problems may take longer to diagnose. It may be necessary to allow the intermittent problem to get worse before it can be diagnosed properly.

  • If the P0189 trouble code does come back immediately, find the fuel temperature sensor connector. Checks the reference voltage and ground signals using a digital volt ohmmeter.

  • If there is no voltage, they will examine the continuity and resistance on the reference circuit of the Power Control Module (PCM).

  • Tests the system again after replacing or repairing damaged wiring or connectors.

  • They will use an oscilloscope to test continuity and resistance of the ground circuits. These results should match the specifications of the manufacturer.

  • Once you are able to ascertain a reference voltage and ground signal, they should check the waveform patterns by connecting the oscilloscope to the fuel temperature sensor wire. Referencing the live data, they will check to see if that waveform pattern matches the specifications of the manufacturer.

  • A high waveform frequency means that the fuel contaminants are high. This can be determined by comparing sensor waveform frequency with real fuel composition.

  • A fast waveform pulse also means that the fuel temperature is high. This can be determined by comparing the sensor waveform pulse width data with real fuel temperature data.

  • There could be an issue with the Power Control Module (PCM), if the data that has been collected matches the real conditions of these components. However, this is unlikely to be the issue.

  • The fuel temperature sensor will need to be replaced if the data that was collected does not match the real conditions.

  • To ensure that the repair is successful, test the fuel system again.

Common mistakes when diagnosing the P0189 code

The fuel temperature sensor is often replaced when it is not the actual cause of the malfunction. It is important to inspect all components of the fuel temperature sensor as other repairs may be necessary.

How serious is the P0189 code?

In some cases, the P0189 trouble code will be a serious concern. It can prevent the car from starting in addition to poor driving performance.

In other cases, when there are no symptoms, the P0189 trouble code is not considered serious. It is still important to have this issue addressed immediately, whether or not symptoms are present.

What repairs can fix the P0189 code?

  • Repairing broken fuel temperature sensor wires
  • Repairing any bad grounds
  • Repairing broken fuel temperature sensor connector
  • Replacing the fuel temperature sensor
  • Replacing the fuel pump
  • Replacing the power control module (much less common)

Additional comments for consideration regarding the P0189 code

It may be necessary to replace the entire fuel pump, instead of just the fuel temperature sensor. In most vehicles, the fuel temperature sensor cannot be replaced separately because it is built into the fuel pump. Nonetheless, the diagnostic procedure should be performed to prevent a misdiagnosis.

It is also important to note the growing popularity of flex fuel vehicles. The fuel temperature sensor measures ethanol separate from other contaminants, is programmed to operate differently than fuel temperature sensors in other vehicles.

Need help with a P0189 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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