P246C is a common DPF fault code on Mercedes diesel models. It means the ECU attempted to perform a regeneration cycle but was unable to complete it – but that can be caused by a low fuel level, a faulty temperature sensor, a blocked DPF, or simply interrupted driving. This page breaks down the causes ranked by cost, what to check first, and whether you should keep driving.
P246C means the ECU attempted a DPF regeneration but couldn't complete it – typically because the vehicle was turned off mid-cycle, fuel was too low, a sensor was faulty, or there's an underlying engine fault. On most Mercedes diesels, this is a straightforward fix, often requiring only a forced regeneration or a sensor replacement.
Do not assume the DPF is faulty – a simple forced regeneration or a £100 sensor replacement often fixes it. Full diagnostic order below.
In a Mercedes diesel equipped with a DPF (Diesel Particulate Filter), the ECU periodically initiates a regeneration cycle – a process that raises the temperature inside the DPF to around 600°C to burn off accumulated soot. P246C is logged when the ECU attempts to start or complete a regeneration cycle but is unable to finish it. This could be because the driver turned the engine off mid-cycle, the fuel level was too low, a temperature sensor is faulty and preventing the ECU from starting the regeneration, or the DPF is too blocked to regenerate successfully. The code is a diagnostic flag, not a death sentence – it tells you that a regeneration attempt failed, but it doesn't tell you why. This code appears across the full range of Mercedes common-rail diesels, from the OM651 four‑cylinder to the OM642 V6 and the newer OM654, and the diagnostic approach is similar regardless of which engine triggers it.
Ordered by how often they are the real culprit – and by typical cost, so you can sanity-check any quote you've been given.
| Cause | Likelihood | Typical Cost (fitted) | Notes |
|---|---|---|---|
| Interrupted regeneration (driver turned off engine) | Very High | £100–£200 | A forced regeneration using diagnostic equipment is the cheapest fix |
| Low fuel level (below 1/4 tank) | High | £0 (top up) | Regeneration won't run if fuel is too low – simple top-up may clear the code |
| Faulty temperature sensor (P244A/P244B) | Medium | £100–£250 | If the ECU can't read temperature, it won't start regeneration |
| Underlying engine fault (boost leak, injector) | Medium | £300–£1,000+ | Any fault preventing the engine from reaching 600°C for regeneration |
| Severely blocked DPF (soot accumulation) | Low | £900–£1,500 | If the DPF is too blocked, regeneration won't work – cleaning or replacement needed |
Cost figures [PATTERN DATA] – indicative independent‑specialist pricing, based on common Mercedes DPF repairs.
Ensure fuel level is above 1/4 tank. If the regeneration was interrupted by turning off the engine, a simple forced regeneration may be all that's needed.
A specialist can check if the ECU has logged regeneration attempts and see what conditions prevented completion – often the quickest diagnostic.
If temperature sensors (P244A/B) are faulty, the ECU won't start regeneration. These are cheap and easy to replace.
Boost leaks, faulty injectors, or EGR issues can prevent reaching regeneration temperature.
If steps 1–4 are clear and regeneration still fails, the DPF may be too blocked to regenerate.
Our diagnostic wizard follows the same order, or confirm your engine with the registration lookup.
Conditionally, yes – but get it diagnosed within days. P246C indicates that a regeneration attempt has failed. If the DPF warning light is illuminated, you should continue driving as normal to allow the next regeneration attempt to start. However, if the warning light is flashing or the vehicle is in limp mode, prolonged driving is not recommended. Short journeys to a specialist are acceptable, but repeated failed regeneration attempts can lead to a blocked DPF and more expensive repairs.
Yes – if the DPF warning light is amber, continue driving as normal. The ECU will attempt another regeneration when conditions are right. However, if the light is flashing or the car is in limp mode, avoid long journeys and get it checked promptly.
No – interrupted regeneration is the most common cause. A simple forced regeneration or topping up the fuel often resolves it. Replacement is only needed if the DPF is too blocked to regenerate.
Only temporarily. The ECU will attempt another regeneration, and if it fails again, the code will return. It's better to address the underlying cause.
Expect £100–£200 at an independent Mercedes specialist – often the cheapest fix. Many specialists will include a regeneration as part of a diagnostic check.
For Mercedes, the repair‑to‑value threshold is 70% – if the cost of the repair (including diagnostics and parts) exceeds 70% of the car's current market value, scrapping may be the more sensible financial decision. Always get a current valuation before committing to major work.
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