What the P0547 Code Means
P0547 means that the PCM is reading a malfunction in the exhaust gas temperature sensor circuit.
What causes a P0547 code?
The exhaust gas temperature (EGT) sensor is located in the exhaust stream, and sends input voltage readings to the PCM. When system voltage is outside of factory parameters, it will cause a code to be stored, illuminating the malfunction indicator lamp (MIL).
Loose, broken, burned or corroded wiring/terminals/connectors are commonly at fault. Other causes may include an internal short in the sensor, a ground short in the sensor, a failed sensor , a severe exhaust leak from the sensor or an aftermarket exhaust system that lowers exhaust back pressure.
What are the symptoms of a P0547 code?
There may be no drivability symptoms other than an illuminated MIL.
How does a mechanic diagnose a P0547 code?
EGT sensors are used in gasoline engines, diesel engines and turbocharged engines. Exhaust gas temperature sensors are usually a two-wire sensor, situated upstream from the catalytic converter in the exhaust downpipe. In diesel engines, though, the EGT will likely be located in the exhaust system near the diesel particulate filter. Turbocharged engines may locate the EGT sensor near the turbocharger, in the exhaust return/input pipe.
EGT sensors are of the temperature-reactive resistor variety, and are supplied with a low-voltage (usually 5 bolts) power wire and a ground wire.
As exhaust gas temps pick up, the EGT sensor’s resistance decreases, allowing an increase in the feedback voltage signal the PCM. As the exhaust gas temps decrease, with the engine off and cooling down, circuit resistance increases and feedback voltage to the PCM drops.
The PCM reads these variations in voltage as changes in EGT and uses this information to adjust ignition timing and fuel metering to regulate EGT and protect the catalytic converter. A technician will need an OBD-II scanner/code reader and a digital volt/ohmmeter for diagnosis. An infrared thermometer equipped with a laser pointer can also be helpful.
Inspect all wiring and connectors, and repair/replace any damaged, disconnected, corroded or shorted wiring, connectors and components as needed. Retest the system to see if repairs were successful. If all wiring, connectors and components (including fuses) seem to be in good working order, connect the scanner/code reader to the diagnostic port. Record any stored codes and freeze frame the data. This information can be useful in diagnosing an intermittent condition.
Clear the codes and test drive the vehicle to see if codes return.
If codes don’t immediately return, there may be an intermittent condition which may have to be allowed to worsen (or see if it returns) in order to make a proper diagnosis.
Visually inspect the EGT sensor and system circuitry. Closely examine any areas where wiring or connectors are close to hot exhaust parts.
Repair/replace any damaged, burned or corroded wiring or connectors. If none seem to be present, disconnect and remove the EGT sensor.
Using the digital volt/ohmmeter, check the EGT sensor’s resistance. Resistance is usually in the 150 ohm range, but check manufacturer’s specs. Resistance of under 50 ohms is usually cause to replace the sensor.
If resistance seems to be within spec, reconnect the leads of the digital volt/ohmmeter and heat the EGT sensor with a heat gun.
Watch the digital volt/ohmmeter’s screen to see if the resistance level decreases smoothly as the EGT sensor is heated up.
If resistance level stays high while the EGT sensor heats or stays low as it cools, replace the sensor.
If everything has checked out to this point, turn the vehicle’s key to the “on” position and check for a voltage reading and ground signal at the EGT sensor’s electrical connections. If there is no low-voltage reading on the signal wire, disconnect the PCM connector and use the digital volt/ohmmeter to perform a continuity test on the wire itself.
If the wire checks OK for continuity, the PCM may be faulty. Remember that PCM failure is rare and will require reprogramming if the unit is replaced.
If no ground can be found, locate the source and check for continuity. Repair/replace any open or shorted wiring or connectors if needed.
Common mistakes while diagnosing P0547 code
Often the downstream O2 sensor is mistaken for an EGT sensor, or technicians believe that the EGT sensor is part of the heated O2 sensor. Replacement of the O2 sensor will not fix the problem or lead to a successful diagnosis.
How serious is a P0547 code?
A P0547 code may not cause immediate drivability problems, but can mean a failed emissions test.
What repairs can fix a P0547 code?
- Replacement of the EGT sensor
- Repair or replacement of any burned, loose, corroded or shorted wiring or connectors.
Addition comments for consideration for P0547 code
High performance aftermarket exhaust systems can result in a P0547 code, due to lowered back pressure (especially when the catalytic converter is left off). In these systems, the problem can be rectified by leaving the EGT sensor disconnected and installing a 2.5 ohm inline resistor between signal and ground wires. The PCM will then read this as sensor resistance and will not register a code.
Need help with a P0547 code?
YourMechanic offers certified mobile 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.