Mercedes EGT sensor fault codes: P2031, P2032, P2033, P2080 and P2081

If your Mercedes has stored P2031, P2032, P2033, P2080 or P2081, the fault sits in the exhaust gas temperature (EGT) sensor circuit. These are among the most commonly misdiagnosed codes on a modern Mercedes diesel, because the sensor that reports the problem is very often not the part that has failed.

What each code means

• P2031 – Exhaust gas temperature sensor circuit, bank 1 sensor 2
• P2032 – Exhaust gas temperature sensor circuit low, bank 1 sensor 2
• P2033 – Exhaust gas temperature sensor circuit high, bank 1 sensor 2
• P2080 – Exhaust gas temperature sensor circuit range or performance, bank 1 sensor 1
• P2081 – Exhaust gas temperature sensor circuit intermittent, bank 1 sensor 1

What the EGT sensors actually do

Your Mercedes uses several exhaust gas temperature sensors positioned around the turbocharger and the diesel particulate filter. The engine ECU relies on them to know how hot the exhaust is at each point. That temperature reading is what decides whether a DPF regeneration can safely start, how long it runs, and when it must be stopped to protect the turbo and the filter.

When one of those readings goes missing or stops making sense, the ECU loses the information it needs to run a regeneration. It will usually take the safe option and stop trying.

Symptoms you are likely to notice

• Engine management light on, sometimes with the DPF warning light
• The car dropping into limp mode, particularly under load or on a motorway run
• Regenerations that start and never complete, or that seem to happen constantly
• Rising fuel consumption and a noticeable loss of power
• A smell of hot exhaust or unburnt diesel after a longer journey

Why the sensor is often not the problem

This is the part worth understanding before you authorise any work. An EGT code can be caused by the sensor itself, but it can just as easily be caused by something the sensor is correctly reporting.

Genuine sensor-side causes include the element degrading after years of heat cycling, wiring chafed where the loom runs close to the exhaust, corroded or water-damaged connectors, and a sensor that has seized in its thread and been damaged during a previous repair.

But a blocked or ash-loaded DPF will drive exhaust temperatures outside the expected range and set the same codes with a perfectly good sensor fitted. So will a failing turbo, a leaking injector, or a boost leak. Replacing the sensor in those cases costs you the part, the labour, and the fault comes straight back.

How we diagnose it

We read the live data rather than just the stored code. Comparing what each EGT sensor is reporting against the others, and against what the ECU expects at that load and temperature, shows quickly whether a sensor is lying or telling the truth about a genuine exhaust problem. We check differential pressure across the DPF, soot and ash loading values, and regeneration history, then test the sensor circuit itself for resistance and wiring faults before condemning anything.

That order matters. It is the difference between fixing the fault once and replacing parts until the light goes out.

Book your Mercedes in

We are an independent garage on Sloper Road in Cardiff and we work on all makes, Mercedes included, with dealer-level diagnostic equipment. If your Mercedes has stored any of these codes, call us on 02920 220 380 and we will tell you what we would check first.

See also our vehicle diagnostics service, the full Mercedes fault code list, and our car servicing in Cardiff.