P0188 trouble code definition
Fuel Temperature Sensor “B” Circuit High Input
What the P0188 code means
The fuel temperature sensor identifies the presence of contamination, such as water, ethanol, or dirt. It also measures the fuel temperature inside the fuel tank to make sure the temperature of the fuel remains within the appropriate range.
If the fuel temperature goes outside the predetermined range, the fuel temperature sensor will send a signal to the power control module (PCM), which then stores the P0188 trouble code.
Depending on the type of vehicle, the Check Engine Light may come on immediately or after several failure cycles.
What causes the P0188 code?
A fuel pump failure is most often the cause of the P0188 trouble code. Other possible causes are a failed temperature sensor, or temperature sensor wiring that is broken, shorted out or damaged in some way. Although it is rare, it is also possible that there is a problem with the power control module (PCM).
What are the symptoms of the P0188 code?
- Sometimes there will be no symptoms at all
- Check Engine Light is on
- Car has hesitation
- Car will not start
- Car will stutter when it is accelerating
- Other fuel system codes stored in the power control module (PCM)
How does a mechanic diagnose the P0188 code?
Inspects wiring and connectors for damage that would make repair necessary
Uses an OBD-II scanner to get the trouble codes and freeze frame data from the power control module (PCM)
Clears the codes and does a test drive to see if the code returns
If the P0188 trouble code does not immediately return, an intermittent problem is possible. These are challenging and may need to worsen before making a diagnosis.
If the P0188 trouble code returns immediately at the fuel temperature sensor connector, they will check reference voltage and ground signals with a digital volt ohmmeter.
If there is no voltage, they will use a digital volt ohmmeter to check for continuity and resistance on the reference circuit.
If necessary, replaces connectors and wiring that is exposed or shorted and tests the system again.
If there is no ground signal, they will use an oscilloscope to test continuity and resistance on the ground circuits to see if the results match the specifications that are provided by the manufacturer.
If there is both a reference voltage and ground signal, they will connect the oscilloscope to the fuel temperature sensor signal wire to observe waveform patterns. This should match the specifications that are provided by the manufacturer as well. They will be able to interpret the results from the live data.
Compares sensor waveform frequency with actual fuel composition. If the frequency is high, this means that contaminants in the fuel are high as well.
Compares the fuel temperature sensor waveform pulse width data with actual fuel temperature data. If the pulse is fast, this means that the fuel temperature is high.
If the data that has been collected does match the verified conditions, there could be a problem with the power control module (PCM). However, problems with the powertrain control module (PCM) do not happen often.
If the data that has been collected does not match the verified conditions, the fuel temperature sensor will need to be replaced.
Test the fuel system to make sure the repair is successful.
Common mistakes when diagnosing the P0188 code
The most common mistake when diagnosing the P0188 trouble code is when a determination is made that the fuel temperature sensor needs to be replaced without first inspecting the other parts of the fuel system.
All wires and grounds should be inspected and ruled out as the cause before the sensor is replaced.
How serious is the P0188 code?
If the vehicle is not showing any symptoms while the P0188 trouble code is present, this code is not considered a serious one, but one that should be addressed in a timely manner.
However, when the symptoms of the P0188 trouble code are ones which cause driveability problems, this code is serious.
What repairs can fix the P0188 code?
- Repairing any fuel temperature sensor wires that are broken, shorted, frayed or damaged
- Repairing any damage or corrosion of the fuel temperature sensor connector
- Replacing the fuel temperature sensor
- Replacing the fuel pump
- Replacing or reprogramming the power control module (PCM) if necessary
Additional comments for consideration regarding the P0188 code
When the fuel temperature sensor is faulty, you may be required to replace the entire fuel pump. The fuel temperature is built in to the fuel pump in most vehicles and cannot be replaced on its own. The diagnostic procedure should still be performed prior to making this conclusion, as to prevent a misdiagnosis.
Flex fuel vehicles are becoming more popular. These vehicles can operate effectively with more ethanol that older vehicles. In flex fuel vehicles, the fuel temperature sensor will measure ethanol separately than the other contaminants in the fuel.
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