P0548 code definition
The P0548 code occurs when the powertrain control module has sensed some sort of fault in the exhaust gas temperature sensor circuit.
What the P0548 code means
A P0548 is an OBD-II generic code that means there is an issue with the exhaust system gas temperature sensor. The PCM detects voltage changes in the sensor, and interprets the data as exhaust gas temperature. The PCM can then alter the ignition timing or air to fuel ratios in order to decrease the exhaust gas temperature as a way of preserving the catalytic converter. If it detects that variations in the voltage fall outside of the vehicle manufacturer’s suggested levels, the code is created.
What causes the P0548 code?
The typical reasons for the P0548 code are:
- Defective sensor
- Extreme exhaust leak upstream of the sensor
- Internal short in the exhaust gas temperature sensor
- Terminals and connectors that are broken, burnt, corroded or loose is the most common cause
- Use of aftermarket exhaust systems creating back pressure
What are the symptoms of the P0548 code?
The P0548 code is accompanied by only minimal symptoms that include the service engine warning lighting on the dashboard and the code being stored.
How does a mechanic diagnose the P0548 code?
When diagnosing the P0548 code, the technician is going to use the OBD-II scanner, but begins by clearing codes and retesting. They note the freeze frame data and when the issue appears, dealing with any other codes that may be underlying causes. They then do a visual inspection of wires and connections, making sure to repair or replace all loose, corroded, damaged or disconnected components before retesting to see if the code is still appearing.
If so, they look at the exhaust circuitry near the hottest points of the exhaust system and do a check of the sensor’s resistance and voltage. A heat gun is used to heat the sensor and then it may be replaced. The technician may also test the PCM and replace that if needed.
Common mistakes when diagnosing the P0548 code
It is not unusual for a technician to mistake oxygen sensors for the exhaust gas temperature sensor, or to believe that both sensors are contained in a single unit. The P0545 code, though is due to the exhaust sensor and simply swapping out the oxygen sensors will not repair the issue.
How serious is the P0548 code?
The P0548 code cannot prevent the car from running, but it can be the result of high temperatures within the exhaust system, and this can lead to the destruction of the catalytic converter or the system circuitry.
What repairs can fix the P0548 code?
The repairs needed to address the P0548 code can include:
- Using the OBD-II scanner to check the code and then clearing it and retesting the vehicle after a test drive to be sure it is an actual issue. Using the data and freeze frame information, the technician can then perform a visual inspection of all wiring.
- Repairing or replacing electrical components and retesting. If the code remains, the tech examines the exhaust gas temperature sensor, its circuitry, and all wiring and components in the areas where exhaust heat is highest.
- If the code remains, the sensor’s resistance is checked with an ohm meter to see if it falls within the manufacturer’s levels. If so, a heat gun is used on the device to see if resistance decreases when heated. If it does not, the sensor is bad and is replaced.
- The PCM’s continuity can be tested, and it can also be replaced if necessary.
Additional comments for consideration regarding the P0548 code
The need to replace any control modules is very rare, and yet it could be possible. If all of the diagnostic do not reveal any issues with the exhaust gas temperature sensor, and the electrical circuitry is in working order, a scan of the PCM may be needed to determine if the unit or some part of the CAN Bus is a problem.
Need help with a P0548 code?
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