What Is P0545?
P0545 is stored when the ECU detects a lower than expected voltage from exhaust gas temperature (EGT) sensor 1. EGT sensors are used primarily on diesel engines to monitor the temperature of exhaust gases at various points in the exhaust system - typically before and after the DPF.
These sensors are critical for DPF regeneration management. If the ECU cannot trust the EGT sensor reading, it may prevent active regeneration from occurring, leading to DPF blockage over time. A circuit low fault usually points to a short to earth in the wiring or a failed sensor.
Common Symptoms
- Engine management light on
- DPF regeneration not completing
- DPF warning light
- Reduced engine performance
- Increased fuel consumption
- Possible limp mode on some vehicles
Common Causes
OBD Fault Code Plain English Guide
- 100 most common UK fault codes in plain English
- A severity rating for every code so you know what can wait
- Causes and next steps listed for each fault
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How to Diagnose P0545
Inspect the Sensor Wiring
EGT sensors are mounted directly on the exhaust and their wiring is subject to extreme heat. Inspect the wiring carefully for melted insulation, broken wires, or chafing near the exhaust pipe. This is the most common cause of P0545.
Check Sensor Connector
Disconnect the EGT sensor connector and inspect for corrosion or damaged pins. Clean with contact cleaner and reseat. Clear the code and retest.
Measure Sensor Resistance
EGT sensors are thermocouples or NTC thermistors. With the engine cold, measure resistance at the sensor terminals. Compare to manufacturer specification. Out-of-range resistance indicates a failed sensor.
Check Reference Voltage
With ignition on and connector plugged in, back-probe the signal wire. No reference voltage from the ECU side indicates a wiring fault between ECU and sensor.
Replace the Sensor
If wiring is intact and the sensor tests faulty, replace it. EGT sensors on high-mileage diesels frequently fail due to heat cycling fatigue. Use an OEM or quality aftermarket replacement.
Verify DPF Operation
After replacing the sensor and clearing the code, run a long motorway drive to trigger a DPF regeneration cycle and confirm the system is operating correctly.
Verdict
Inspect all wiring near the exhaust first - heat damage is the leading cause of P0545. If wiring is intact, test and replace the sensor.
P0546 - The Same Sensor Failing In The Other Direction
P0545 and P0546 are mirror images: the exhaust gas temperature sensor circuit reading low versus reading high. Electrically they are the two ends of the same failure map - an EGT sensor is a resistance element, so an open circuit pins the reading at one extreme and a short pins it at the other. Which code you get for which fault depends on the car's sensor type, which is why the honest test is the one on this page: measure the sensor's resistance and compare its live reading against a neighbouring EGT sensor from cold, when every sensor on the car should agree with the weather.
These sensors live in the hottest, most corrosive spot on the vehicle, and on diesels they are not optional extras - the ECU needs a trustworthy EGT reading to run DPF regenerations safely, and many cars quietly suspend regens when one of these codes is stored. Left alone, that turns a £60 sensor into a blocked filter problem, so a P0546 on a diesel deserves attention within days rather than months. When replacing one, thread care matters: the sensor seizes into hot exhaust steel, so treat it like the glow plug problem - penetrating oil, a warm engine and patience beat force every time.
