P0545 and P0546: exhaust gas temperature sensor circuit

Exhaust gas temperature sensors sit in the hottest, dirtiest part of the vehicle and are expected to report accurately for years. They are consumables, and on a modern diesel there are usually several of them.

Code	Meaning
P0544	EGT sensor 1 circuit
P0545	Circuit low input
P0546	Circuit high input
P2031, P2032	Sensor 2 equivalents: P2031 to P2036

What they do

Turbocharger protection. Exhaust temperature above a limit means the ECU reduces fuelling to protect the turbine. Without a trustworthy reading it takes the conservative option and limits power.

DPF regeneration control. Burning off soot requires the filter to reach roughly 600 °C. The ECU raises temperature by injecting extra fuel late in the cycle and uses EGT sensors to confirm it worked and to stop before something melts.

Catalyst and SCR management on vehicles with the full after-treatment stack.

That second function is why an EGT fault has consequences well beyond a warning lamp: regeneration may be inhibited entirely, and soot then accumulates until the filter blocks.

DPF light on, what to do and P2002 and P2463 DPF efficiency and soot.

The oil dilution consequence

Regeneration works by injecting extra fuel late in the combustion cycle to raise exhaust temperature. Some of that fuel washes past the bore and ends up in the sump.

A car that keeps attempting regeneration and never completes it does this repeatedly. The dipstick level rises, and diluted oil does not protect bearings.

Check the oil level on any diesel with a regeneration fault. Above maximum means change it, not top it up: oil light flickering at idle.

Why they fail

Heat cycling. From ambient to 700 °C and back, several times a day, for years.

Vibration, which fatigues the wiring at the point it leaves the sensor body.

Corrosion at the connector, which typically sits in the underbody airflow.

Physical damage during exhaust work — the wiring runs along the exhaust and is easy to snag.

Seizure in the thread, which is not a fault until you try to remove it. An EGT sensor that has been in place for ten years frequently shears off. Budget for that possibility before starting.

Reading the values

Log all EGT sensors together during a drive.

Observation	Meaning
All read within a few degrees at cold start	Sensors plausible
One reads far off from cold	That sensor is faulty
Fixed at an extreme (−40 or 900+)	Circuit fault, not a measurement
Rises smoothly under load	Normal
Never rises during a regeneration	Sensor or regeneration failure

The cold comparison is the decisive test, exactly as for coolant and intake sensors. After a night parked, every EGT sensor must read approximately ambient.

What a regeneration should look like

Worth knowing to interpret the data:

1. Soot load reaches the trigger threshold.
2. The ECU commands post-injection.
3. EGT rises steadily, reaching around 600 °C at the filter.
4. Temperature holds for ten to twenty minutes.
5. Soot load falls sharply.

If EGT never climbs, the regeneration is not happening. If EGT climbs and soot does not fall, the filter may be blocked with ash rather than soot: P242F DPF ash accumulation.

DPF forced regeneration scanner procedure.

Symptoms

• Reduced power or limp mode.
• DPF warning lamp, because regeneration stopped working.
• Increased fuel consumption from repeated failed regeneration attempts.
• Oil dilution — post-injection fuel that does not burn ends up in the sump. Check the dipstick: above maximum means change the oil.

That last point matters on any diesel that has been failing regenerations for a while.

Do not delete it

Removing or spoofing EGT sensors, like deleting the DPF itself, is illegal in most markets, fails inspection, and removes the protection that keeps the turbocharger alive.

It is also detectable in the ECU calibration: ECU remap and chip tuning detection.

Sequence

1. Compare all EGT sensors from cold — the fastest identification.
2. Check the connector for corrosion and heat damage.
3. Inspect the wiring along the exhaust for chafing.
4. Log a drive and watch whether temperature rises under load.
5. Check soot load and whether regenerations are completing.
6. Replace the sensor, allowing for a seized thread.
7. Check oil level for dilution from failed regenerations.

Log every exhaust temperature sensor from a cold start — an ELM327 adapter and the free tier of the app are all it takes. The one that disagrees with the others before the engine has run is the one to replace.